5 Secret Tips to FIX ANY CAR

Summary

This script from a technical trainer emphasizes five key areas to enhance automotive diagnostic skills. It underscores the importance of a structured diagnostic process, starting with information gathering before delving into physical tests. The trainer highlights mastering electrical diagnostics, understanding sensor circuits, especially voltage divider circuits, and the significance of live data for recognizing normal vehicle operation. Lastly, the script advocates for the effective use of wiring diagrams, suggesting ways to interpret them accurately for successful diagnostics.

Takeaways

• 🔍 The importance of having a structured diagnostic process is emphasized, with 'FIXED IT' being introduced as a methodical approach to automotive diagnostics.
• 📝 Information gathering is crucial before starting diagnostics, including vehicle history, symptoms, and initial observations upon approaching the vehicle.
• 🔌 Understanding electrical fundamentals is key for effective diagnostics, especially the proper use of a multimeter for measuring voltage drop and ensuring circuits are switched on during testing.
• 💡 The concept of voltage divider circuits in sensor diagnostics is introduced, explaining how sensor resistance changes affect the voltage signal read by the control unit.
• 🚫 Fault codes related to sensor circuits, such as 'signal too high' or 'signal too low', are often indicative of electrical issues like short circuits or open circuits.
• 📊 Live data analysis is highlighted as an essential skill, with the suggestion to familiarize oneself with normal values and how they change under different operating conditions.
• 📚 The value of wiring diagrams in diagnostics is discussed, with advice on how to interpret them effectively, especially when it comes to identifying power supplies, grounds, and sensor signals.
• 🔧 Practical tips for using wiring diagrams are provided, including identifying fixed points like grounds and powers, and understanding switch functions.
• 🆚 The differences between OEM and generic wiring diagrams are outlined, with a preference for OEM diagrams for their detailed and manufacturer-specific information.
• 🛠️ The script encourages technicians to build a library of known good data and to use resources like 'mechanic mindset' for further diagnostic support and training.

Q & A

What is the first step in the diagnostic process discussed in the script?

The first step in the diagnostic process is to collect as much information as possible about the vehicle's history, any accidents, and other observations before starting any physical inspection or testing.

What does the acronym 'FIXED IT' stand for in the context of the diagnostic process?

The acronym 'FIXED IT' is not explicitly defined in the script, but it is mentioned as a diagnostic process that the speaker's organization, Mechanic Mindset, is passionate about. It is implied that each letter represents a step in their diagnostic process.

Why is it important to understand how a multimeter works in automotive diagnostics?

Understanding how a multimeter works is crucial because it is a difference measuring tool used to measure voltage drop, which is essential for accurate electrical testing in automotive diagnostics.

What is the significance of testing electrical circuits with the circuit switched on?

Testing electrical circuits with the circuit switched on is significant because it provides a loaded condition, allowing for accurate readings and preventing misdiagnoses that could occur with an unloaded circuit.

What is a voltage divider circuit and why is it important in sensor diagnostics?

A voltage divider circuit is a circuit that splits a voltage across two resistors, which is important in sensor diagnostics because it allows the sensor to vary the voltage based on its input, such as temperature or pressure, providing a signal to the control unit.

What does the term 'pull-up' and 'pull-down' resistor refer to in the context of sensor circuits?

In the context of sensor circuits, 'pull-up' refers to a resistor that connects the sensor to a positive voltage supply, while 'pull-down' refers to a resistor that connects the sensor to ground. These terms describe the direction of the voltage reference for the sensor signal.

Why is it recommended to learn and understand wiring diagrams for successful diagnostics?

Understanding wiring diagrams is recommended because it provides a clear understanding of how the vehicle's systems are interconnected, which is essential for accurate and efficient diagnostics.

What is the general maximum voltage drop limit along a piece of wire in automotive electrical systems?

The general maximum voltage drop limit along a piece of wire in automotive electrical systems is 0.5 volts.

How can live data help in diagnosing automotive issues?

Live data helps in diagnosing automotive issues by providing real-time sensor readings and system performance metrics that can indicate normal operation or potential malfunctions.

What is the importance of having a library of known good data in diagnostics?

Having a library of known good data is important in diagnostics because it serves as a reference to compare against the current vehicle's data, helping to identify deviations that may indicate a problem.

Outlines

00:00

🔍 Diagnostic Process and Information Gathering

The paragraph emphasizes the importance of a structured diagnostic process in automotive diagnostics, which begins with gathering as much information as possible before starting physical inspections. The speaker introduces their diagnostic process called 'FIXED IT' and highlights the need to understand the vehicle's symptoms and history. They also stress the significance of observing the vehicle's reactions to basic operations like unlocking the door or cranking the engine, which can provide valuable diagnostic clues. The speaker suggests collecting all evidence before making the first test, aiming for an accurate starting point in diagnostics.

05:03

🔌 Mastering Electrical Diagnostics

This section focuses on the fundamentals of electrical diagnostics, which the speaker considers a common weak point for many technicians. The speaker provides tips on using a multimeter effectively, emphasizing that it is a difference-measuring tool. They explain how to measure voltage drop and the importance of testing circuits when they are switched on to get accurate readings. The speaker also discusses how to test for voltage drop in both live and ground circuits, and the significance of recognizing a 'flat zero' in voltage readings. They conclude with a general guideline for voltage drop limits in automotive electrical systems.

10:05

📡 Understanding Sensor Circuits and Voltage Dividers

The speaker delves into sensor circuits, particularly the voltage divider circuit, which is crucial for understanding how sensors work within a vehicle's control unit. They explain the concept using an analogy with light bulbs and resistors, illustrating how the voltage changes based on the sensor's resistance. The speaker clarifies the difference between a 'pull-up' and 'pull-down' resistor and how most sensors use a ground path through the control unit for a cleaner signal. They also discuss how sensor signals can lead to fault codes such as 'signal too high' or 'signal too low' and how these codes relate to open or short circuits.

15:07

💻 Live Data Analysis and Expectations

The paragraph discusses the importance of understanding live data in automotive diagnostics. The speaker addresses the common challenge of knowing what data readings should be under normal conditions. They suggest that technicians should familiarize themselves with good data values by observing different signals on various cars and under different operating conditions. The speaker encourages the creation of a 'library of known good data' to aid in diagnostics and mentions a diagnostic coach program that can help with this process.

20:10

🔗 Wiring Diagrams: Key to Effective Diagnostics

The speaker highlights wiring diagrams as a critical tool for successful diagnostics. They discuss the benefits of using original equipment manufacturer (OEM) wiring diagrams for their detailed information compared to generic systems. The paragraph provides tips on how to effectively use wiring diagrams, such as identifying power supplies, grounds, and understanding switches and their functions. The speaker also touches on the use of wire codes and thickness to deduce the function of wires in a circuit, emphasizing the importance of this knowledge for accurate diagnostics.

25:11

📲 Advancing Diagnostics with Mobile Apps and Resources

In the final paragraph, the speaker introduces a mobile app and a website designed to enhance diagnostic skills. They encourage technicians to sign up at mechanicmindset.com and use the code 'YouTube' to get a free trial of the diagnostic coach. The speaker suggests that these resources can help take diagnostics to the next level by providing access to valuable information and tools.

Keywords

💡Diagnostic Process

The diagnostic process refers to the systematic approach technicians use to identify and solve vehicle issues. In the video, the speaker emphasizes the importance of a structured diagnostic process before using tools like scan tools or multimeters. The 'FIXED IT' process mentioned is a method to ensure technicians gather all necessary information and evidence before making their first test, which is crucial for accurate and efficient diagnostics.

💡Scan Tool

A scan tool is a device used to read and interpret fault codes from a vehicle's computer system. The script mentions that many technicians start their diagnostic process by plugging in a scan tool to read fault codes. However, the speaker suggests that this should not be the first step and that a comprehensive diagnostic process should precede it.

💡Fault Codes

Fault codes are error messages generated by a vehicle's computer when it detects a malfunction. The video script discusses how technicians often rely on these codes as a starting point for diagnostics. The speaker advises that while fault codes are useful, they should be considered part of a broader diagnostic approach.

💡Multimeter

A multimeter is a tool used to measure electrical values such as voltage, current, and resistance. In the script, the speaker explains how to correctly use a multimeter as a difference measuring tool, which is essential for accurate electrical diagnostics in vehicles.

💡Voltage Drop

Voltage drop refers to the decrease in voltage as it travels along a wire due to resistance. The script provides an example of measuring voltage drop across a circuit to diagnose issues. Understanding voltage drop is crucial for diagnosing problems in electrical circuits within vehicles.

💡Sensor Circuits

Sensor circuits are the electrical pathways that connect sensors to a vehicle's control module. The video explains the concept of voltage divider circuits, which are common in sensor circuits. These circuits use a variable resistor (the sensor) to change the voltage signal based on the sensor's input, such as temperature or pressure.

💡Pull-Up and Pull-Down Resistors

Pull-up and pull-down resistors are used in circuits to ensure a known logic level when a switch or sensor is in an open state. The script mentions these resistors in the context of sensor circuits, explaining that they provide a reference voltage for the sensor signal, which is critical for accurate sensor operation and diagnostics.

💡Live Data

Live data refers to real-time sensor and system readings from a vehicle's computer system. The speaker stresses the importance of technicians understanding what 'good' live data looks like for various sensors and under different operating conditions. This knowledge is essential for diagnosing issues by comparing actual readings to expected values.

💡Wiring Diagrams

Wiring diagrams are visual representations of a vehicle's electrical system, showing the connections between components. The script discusses the importance of interpreting wiring diagrams correctly for effective diagnostics. The speaker provides tips on how to use diagrams to identify power supplies, grounds, and sensor signals, which are vital for troubleshooting vehicle systems.

💡OEM Wiring Diagrams

OEM (Original Equipment Manufacturer) wiring diagrams are diagrams provided by the vehicle manufacturer. The video script suggests that technicians prefer OEM diagrams because they are more detailed and accurate compared to generic diagrams. These diagrams are recommended for precise diagnostics and understanding the vehicle's specific electrical system design.

Highlights

Emphasized the importance of a structured diagnostic process, introducing the 'FIXED IT' method.

Highlighted the significance of gathering comprehensive vehicle information before starting diagnostics.

Stressed the value of understanding the diagnostic process to improve efficiency and accuracy.

Explained the concept of using the vehicle's reactions (like fuel pump priming) to gather diagnostic information.

Discussed the importance of checking for voltage drop as an indicator of electrical issues.

Provided tips on using a multimeter effectively for accurate electrical diagnostics.

Highlighted the necessity of testing electrical circuits with the circuit switched on for accurate readings.

Explained the concept of voltage divider circuits and their role in sensor diagnostics.

Discussed how to interpret sensor signals and the implications of signals that are too high or too low.

Described the process of diagnosing sensor circuits by understanding their voltage ranges and fault codes.

Emphasized the need for technicians to familiarize themselves with live data and understand what 'good' data looks like.

Suggested building a library of known good data to compare against during diagnostics.

Highlighted the importance of understanding wiring diagrams for effective diagnostics.

Provided tips on interpreting wiring diagrams, including identifying power supplies, grounds, and switches.

Discussed the use of wire color codes and thickness to aid in diagnosing electrical issues.

Offered advice on using professional resources like Alldata and E-Manual for OEM wiring diagrams.

Encouraged the use of a systematic approach to diagnostics to save time and improve results.

Promoted the use of the 'FIXED IT' diagnostic process poster as a reference tool.

Transcripts

I've trained thousands of technicians on

effective diagnostic techniques since

becoming a technical trainer in 2010 and

I've noticed some of the things that the

best diagnostic technicians do to make

them successful in completing diagnostic

jobs and we're going to look into five

areas that you can start improving in

today to instantly make you better at

Automotive Diagnostics the first thing

to take a look at is diagnostic process

now if you ask most people about what

their diagnostic process is the first

thing they usually say is well we plug

in the scan tool and read the fault

codes and then if you say well what

about if it was a knocking noise from

the rear or what if it was a uh water

leak or something like that then that

gets them thinking about what diagnostic

process is so we're quite passionate

about diagnostic process at mechanic

mindset and we've called ours fixed it

now each one of these letters stands for

a step in the process I'm not going to

go through the whole thing today but I'm

going to take you through the main parts

of it actually you can download and

print this poster in the link below so

in this process the actual Diagnostics

doesn't start until here there are

actually two steps that we want to

perform before we actually start ripping

the car apart and you know prob in wires

with our multimeter and things like that

take this car here for example this is a

crank noar and before we actually start

doing anything we're going to want to

collect as much information as possible

history accidents what else have they

noticed in fact there's a lot of

information that you can collect as soon

as you start going out to that vehicle

for example when you unlock and open the

door you might hear the fuel pump primes

now you know that that part of the

system is working even simply unlocking

the door is telling you that a large

portion of this vehicle system is

operating as it should be and then of

course we're going to switch the

ignition on and try and crank it over

so just the very Act of turning it on

and cranking it over is telling you that

there's lots of things that are working

take the rev counter for example if you

notice the needle moves when you crank

it it shows us that not only is the

engine speed sensor working but the

engine management system is putting that

signal onto the canvas Network and that

signal is making its way way up to the

instrument cluster here massive amount

of information there so after you've

gone ahead and took the time to find all

this evidence you then need to sit down

and put it all together okay so the

engine does crank it's not starting I've

got a crankshaft sensor signal what's

happening with the fuel pressure while I

heard the fuel pump was working have we

got pressure up at the rail all of these

little things ultimately to get you to a

point where you're going to make your

first test and hopefully it's in the the

right place and as long as you do both

of those tasks well you're likely to get

a really good starting point for

Diagnostics save loads of time check out

this video here where we show you a

little bit more about the fixed it

diagnostic process the second thing for

us to work on is everyone's favorite

subject electrical Diagnostics this is

renowned to be everyone's biggest weak

point when it comes to Diagnostics now

I'll tell you one thing that I've

noticed is the people who have got this

massive

have the fundamentals absolutely nailed

so the real basics of electrics that's

all you need to know and you need to be

able to do that very well so here's some

tips to help you get running with

electrical Diagnostics firstly is how

the multimeter is actually working now

the multimeter is a difference measuring

tool so when you put your multimeter on

the battery so we put this on the the

negative or ground that's zero volts on

this lead we put this onto the positive

side we've then got whatever the battery

voltage is so in this case it's 14.2

volts because we've got a battery

maintainer on there so what the

multimeter is doing is taking the

difference between two points zero on

this lead 14.29 on this lead that gives

us a reading of 14.29 volts now that's

really important to remember when you

get on to measuring things like voltage

drop so another tip is to do all of your

electrical testing with the circuit

switched on okay if the circuit's not

switched on it's not loaded and you're

not going to get the accurate readings

and potentially end up with a

misdiagnosis so here we've got a basic

circuit there's 6 volts coming out here

a switch we've got our bulb and then

that comes down to the ground side here

okay so we're going to put our black

lead on the

ground and do our measurements from here

so at the power supply here we've got

5.64 Vols and at the actual bulb we've

got 5.45 volts so a drop of 0 2 so what

you can do is use the meter as a

difference measuring

tool and you can see there we've got

about 02 of a volt that there is a

voltage drop test however if the circuit

is not switched

on it doesn't work so that's how we test

the live side for the ground side we

test in exactly the same way except

we're not looking for a positive voltage

aree 6 volts we're looking for zero

volts okay so ground is just the

opposite of live so if we go on there

and we get Zer volts we know we've got a

good reading here's another tip if you

connect up to a lead and the numbers are

floating around like they are there

that's nothing okay so nothing is

different to Z volt you can see there

that it's a solid zero in fact if we go

back back to the actual ground here

you'll notice that as we go along it

016

006

004 all the way down to dead Zer okay so

you see that flat Zer there that is our

flat zero volts different to nothing

okay so now we've moved the switch over

to the ground side this is something

that catches quite a lot of people out

with Switched Off look we've got our 6

volts at the power supply of course

that's expected because it's a

uninterrupted connection however on the

ground side we've still got 6 volts now

remember all this bulb is is a small

piece of wire okay and it's not been

loaded at the minute so all we've got is

six volts of energy sat there waiting

okay it's not until we turn the circuit

on that we get our Z volt ground on that

side of the B so remember switch the

circuit on before you do any testing do

not disconnect and test because that

could mean that you might miss other

types of faults in the circuit which I'm

going to show you now as for testing for

faults remember the circuit needs to be

switched on okay so you can see here

that we've got some green crusties in

the circuit now the bulb is on but it's

very very dim if we turn that circuit

off we can see that at the bulb we've

got six volts okay remember this is a 6V

circuit so that's good right however

watch what happens when we turn the

circuit on it drops to 2.6 okay again

voltage drop so I've moved the green

crusties onto the ground side now okay

Switched Off we've got 6 volts at the

power

supply switched on 5.72 that's okay that

means that all this part of the circuit

is okay now if we check the ground we've

got 6V Switched Off remember we're not

connected this side to the ground yet

switch it

on we've now got 3 volts that's not okay

it should be as close to zero as

possible regarding your voltage drop

limits it's generally accepted in the

automotive trade to have a maximum of

0.5 volt drop along a piece of wire so

with this circuit here switched on an

acceptable amount would be 12 volts

having a 12.5 volt power supply and on

the ground side a maximum of 0.5 volt

now they are the general limits but

always just take them with a bit of

logic sometimes you might have a reading

of 6 volts however the system might

still be working okay looking at the

bigger picture does this consumer have

enough voltage for itself to do the job

it needs to do taking away the voltage

that's been lost on the wires check out

this short video where we look at

testing electrical circuit with live and

ground switching a little bit more the

third thing to look at is sensor

circuits once you understand the basics

of how a sensor circuit works the

majority of sensor Diagnostics becomes

very very easy in particular we're going

to look at the voltage divider circuit

and you really need to have your basic

electrical

fundamentals absolutely perfect before

you can really understand how this thing

works however I'm going to do my best to

make it really really

easy so if we draw this basic circuit

here with two light bulbs exactly the

same we've got 5 volts at this end a

ground at this end both the light bulbs

would be switched on what do we have in

the middle we should expect roughly half

the voltage 2.5 volts so you can see

that we've got that similar circuit set

up here but we've got a 6vt power supply

both bulbs are connected in series the

bulbs are the same in the middle

here we've got around about half so

sensor circuits are generally made up

like this however all of this

part is

inside the control unit and this part

represents the

sensor so instead of a bulb we have

what's called

a resistor and you might have heard the

term pull up and pull down resistor

if the resistor has 5 volts on this side

of it it's a pull-up

resistor that's then our power supply

down to our

sensor and in many cases this sensor

will be some sort

of variable

resistor with a ground on the other side

however what you will find is that most

sensors actually take a ground

path through the control unit itself

because it's much cleaner and gives us a

more accurate sensor

signal so in this case here this is like

a coolant temperature sensor of course

this signal here is going to change

based on the coolant temperature and how

it does that is that as the temperature

of the coolant or the sensor increases

or decreases the resistance value here

changes that means that the voltage on

this line here is also going to change

let me show you so I'm going to switch

out this bulb here remember this bit

here represents what's inside the

control

module and we're going to

connect this variable

resistor so now we switch the circuit on

we can see here that we've got a value

of around 0 volts so to increase and

decrease that signal voltage we of

course change the resistance on the

sensor which is represented by this here

okay

so by dividing the circuit voltage with

two resistances we make it possible to

have a point where the voltage varies

based on whatever the sensor is given us

so we've already established that the

sensor has a 5V power supply but we

generally say that the sensor has a

working range of between 0.5

volts and 4.5

volts these values aren't set in stone

so they could be a bit wider than this

and of course that wouldn't be true if

it was a 12volt sensor it would be much

higher than that but these are General

values so what we have on the sensor is

a working

range and if this was a temperature

sensor we wouldn't expect it to go

outside of these dotted lines so if that

signal did go outside of the range up to

5 Vol we would say that that signal was

too

high seen that fault code before sensor

signal too high well you may have also

seen the fault code signal too low now

that means that the sensor signal has

gone down to around 0 Vols when you get

a fault code that says circuit too high

or circuit too low they're generally

electrical circuit faults and they're

sometimes accompanied with the method

message uh short circuit to positive or

open circuit or short to negative or

open circuit and sometimes you got to

think well why can't it tell the

difference well let's have a look at how

these fault codes would occur so we've

got our sensor connected here and you

can see that the lowest we can get it to

go is about 05 of a volt and the

highest around about 5.8 okay now if we

make an open circuit in this

circuit here did you see that there

jumped up to 6 volts so it essentially

jumped from its upper range cross the

line to that higher range where is too

high so that's how the control unit

knows the circuit's open circuit the

only other way to get the circuit

voltage over that line is to short it to

positive like this so if we shorted that

to positive that line would then go up

to around about 12 vol it's too high

that's why it can't tell the difference

between an open circuit or a short

circuit to positive okay so I'm going to

demonstrate that to you here we're going

to go on that sensor signal for the fuel

pressure sensor down here and you can

see there that we've got 2 volts okay

now if I disconnect that

sensor you can see there that that

signal has now gone up to 5 Vols okay

now there was a bit of a warning message

in the dash there we should should now

then have a fault code to go with that

which you can see there look fuel

pressure circuit high on the other side

of that then we've got circuit voltage

to low now if we short that signal down

to ground you can see that it goes

nearly all the way to zero so that's

your sensor circuit too low you're shter

ground now the other type of fault code

we've got is if the sensor is given us a

signal that is out of range or is

implausible in that case the control

unit is looking that the signal stays

within a tolerance of

operation so any given operating

temperature engine speed engine load the

signals of the um engine management

system should be within a certain

range so at the point that they go out

of that

range we then get a fault code saying

signal out of range or signal

implausible so take temperature sensors

if the car has been left in the workshop

and it's all cold all of the temperature

sensors should pretty much read the

ambient temperature of the workshop if

it's a bit warmer then of course the

temperature sensors should be a bit

warmer if they're up to temperature then

they should be much higher pressures

with the ignition on most of your

pressures should be reading atmospheric

pressure which is zero bar for gauge

pressure sensors th000 mbar or one bar

for absolute pressure sensors so here

look we disconnected that sensor and you

could see there that the pressure jumped

right up and that's not going to move

now when we start the engine and rev it

so the readings may also correlate to

The Faults that you've got on the system

and we're going to take a look at how

you can help with those types of fault

codes in the next section however if you

want to see a bit more about the voltage

divider circuit check out this video the

fourth thing that you need to work on is

live data now it's really important that

you kind of get to know what to expect

when it comes to live data one of the

biggest complaints that I get from

technicians that I train is that how do

I know what it's supposed to be no one

tells us what it should be you know um

how do I know if that reading there's

correct I understand nothing now there's

no real good answer for that other than

that you need to get to know it yourself

and understand what kind of uh signals

you should be and what data you should

be seeing on those similar types of

engines because they're all pretty

similar so a 2 L petrol on an Audi

you're going to get similar readings to

a 2 L petrol on a BMW that's kind of the

the General Physics of it if you like so

what I suggest you do is take the time

to learn what good values look like um

when you're just doing your regular job

so maybe week one focus on air mass

meter signals for all the different cars

you work on week two take a look at the

map manifold absolute pressure sensors

for all the different cars you work on

the week after that have a look at fuel

pressure temperatures exhaust pressures

and so on until you start to understand

what those values should be on a good

working car the other thing that you're

going to want to do is have a look at

that data under different operating

conditions so what does it look like

with the ignition on what does it look

like when it's cranking what about when

it's idling what about when I rev it up

and take my foot off the accelerator

what happens to that signal and you're

not going to have to take hours and

hours out of your work schedule to do

this if you've already got the tool

plugged in for a diagnosis on a

different problem or a service or

something like that just take one minute

2 minutes just to have a quick look at

it store it in the memory bank and it

will pay you back later I guarantee it

so we're trying to build a library of

known good data inside mechanic mindset

so that if you are stuck you can go and

check it out see if it car relates to

what you've got it's all included in the

diagnostic coach program and you can get

your first month free using the coupon

code month go and check it out so the

fifth thing that you need to work on is

everyone's favorite wiring diagrams

possibly the number one roadblock to

doing better and successful Diagnostics

quickly is getting hold of good

information after that would be

interpreting it properly now if you

really get to learn and understand

wiring diagrams you're natur

understanding how the vehicles work and

operate how these manufacturers put

these systems together because there's

only so many ways you can achieve the

outcomes of what we're doing here so for

the times when you can't get the wiring

diagrams you may already have enough

knowledge to try and work out the system

and test it properly yourself so I'm

going to show you a few tips in a minute

to get the most out of these however

personally I prefer using OEM uh wiring

diagrams where possible you tend to get

a lot more information from the

manufacturer so I like to use uh all

data um that is a professional site I

think in the US you can actually get a

hobbyist version of it and get

individual diagrams there's also a site

called e-manual um I'll leave a link for

that down below and you can get oneoff

OEM manufacturing diagrams from them for

quite a reasonable price otherwise

you're looking at generic systems like

Auto data or haes or Tech Forex now

those systems are really good the

diagrams are generally very generic so

every time you look at a diagram it's

going to look the same however they do

tend to lack important information like

uh wiring colors wire sizes whether the

wies a signal a power or ground which

you you know often get on the manufactur

diagram so anyway let's have a look at

some things you can do okay so the first

thing you want to do when it comes to

diagrams is basically highlight the

things that are definitely true so for

example identifying power supplies and

grounds now you can see down here that

all of these um blue parts are connected

to

ground so we just put gnd D there for

ground so all of these blue ones here

are connected

directly to ground okay that is a fact

okay

so what you can then do is follow them

all the way up this is just a junction

box here so that ground is going to go

all the way up here into this junction

box over to this relay now here's one to

not get tripped up by is that on a

switch it's easy to say it but when

you're actually reading the diagram it's

easy to mess up especially if you're

testing the circuit with it switched off

it might be live on the other side there

okay so remember what we looked at in

our fundamentals earlier make sure

you're testing it switched

on so of course if that's switched on

then that side there is going to be a

ground as well

okay then you've got the powers okay so

if you've got a fuse on a diagram fuses

are

always supplied by power okay live

voltage so you can then follow those

across and then you've got good reliable

diagram to go back onto for your testing

okay um when it comes to components like

actuators we've got this motor here

we've got a a relay coil just up there

it's always going to be a power one side

and a ground the other okay so if you

can identify at least one side of that

circuit as being a power the other side

of it has to be a ground when it's

switched on remember that's the key

thing when it's switched on because you

can see here now this goes down to a

switch now this is a Japanese diagram

from a Suzuki I believe and uh a lot

they've got a lot of these switch types

here it's not very common for uh the

diagrams I'm used to read in however

it's basically a function switch okay so

what you can do is just try and work out

what it's actually trying to do so we've

got the the different positions for the

switch there this is like a rotary type

switch so as you turn the switch it's

it's going to connect the dots of these

different columns there okay so with

this being the washer pump here that you

can see that when we go to wash it

actually connects these two up which is

giv us a

path through the switch to ground okay

so that's that that's the ground path

for the washer and if you were

diagnosing the washer pump that's what

you would have to try and work out

before you could go and kind of test it

accurately so when it comes comes to

looking for sensor signals and stuff

like that as I said uh the manufacturer

diagrams generally have some information

on there but what you can see here for

this position sensor we've got a wire

coming here we've got a bit of a diagram

in the middle here with a with a

resistor and a pointy bit on it so that

pointy bit is likely going to be the bit

that moves and gives us the sensor

signal coming out of here okay um the

other thing with uh the BMW diagrams is

they have this code on all of the wires

see this a s a r s AGR U 5 Vols well

those are codes for the wires and they

give a good indication of what that wire

might be so for example they use U for

power supplies they use M for uh grounds

uh they use a for analog type

signals they might use T for for timed

quick on andof signals like pulse width

modulation and a host of other different

codes too now if you don't have any

codes sometimes you can use the actual

wire thicknesses so if you've got a

module that's got you know lots of

different wires on it generally power

supplies and grounds for actuators will

be slightly thicker than the power

supplies and grounds for sensors so if

we look here the pressure controller for

the EGR valve has a 75 gauge wire yet

the sensor has a 35 gauge wire other

than that you could use the power of of

elimination plus all of the other things

you've learned about how these systems

work to identify which wire might be

which during testing if you want to take

your Diagnostics to the next level

download our new mobile phone app and

sign up at mechanic mindset.com today

use the code YouTube to get your first

month of diagnostic coach absolutely

free