General You have a problem ? Start with this

[kakashi7593]

I really love you guys so I want to help and I hope this thread gets sticked on top.

If you have any problem with your car, it is important to do couple of tests.
The whole point of fixing, actually the MAIN point is.....to find where the fault actually is.

I see so many of you guess, or you go to a mechanic and he drains you out of your money and guesses what the issue might be.
That is not how fixing works.(I mean, maybe I am an idiot and you ARE supposed to randomly replace parts, spend money and hope you get lucky)

I mainly deal in fixing electronics and micro-level components, so for me, understanding this was a life saver.

Its all about localizing where the problem is, as well as where the problem is not, so you do not waste your time and money replacing unnecessary parts.
Keep that in mind at all times.

To localize where the fault is, you need to do few tests, any tests, and observe under what conditions the fault occurs.

Lets say, I will use super random example, you press the button on your key to unlock the car, but it does not unlock.
It could be the key and its internals, it could be key battery, the unit that receives wireless key signal, it could be power to that unit, it could be that unit is not communicating to the main ECU to execute opening command, it could be simply cables not good, heck it could be God fking with you to stress you out...

We can guess all day, but what we simply need to do is start doing tests, it would be smart to do some bigger tests that will point out where the problem is.
Use a tester or go to some place that can test your key, if its even sending signals.
Why this ?
Well if you test out a battery inside a key for its voltage, and it is good, well, do you know if electronics inside the key are good ?
No, you still have no idea if its the key and you can't eliminate it from the equation.
But if you straight up test they key to see if its sending correct signals, and it is, now you eliminate that its not the battery and not electrons in the key, its something in the car.

This is the reason for existence of OBD2.
The codes you read trough the OBD2 system help you figure out where the problem is located exactly.

One time this mechanic friend of mine, brought me a dashboard to fix, he said "I read online its the cold solder joins, just first two..." so I inspected the unit, noticed indeed cracked solder joints but still kept looking to see if any component was burnt etc etc.
I noticed like 10 more cracked solder joints, after new solder, car ran like clock.
I mean, if I do a bad job, I will have to come back and redo it again, waste time, fk that.

Ideally after you finish the job, it would be great to run some tests to see if you solved the issue, if tests are possible to do.

I hope you get the point here.
If your car shuts off randomly , you're supposed to instantly observe, "ohhh what did I just do to make this happen", "did I hit the bump, did I press something, how fast was I doing, what were the RPM" , if some of you are familiar with Freeze Frame Data, this is actually same thing.

If your mechanic is someone who always asks you about the fault, your experience and what happens when and where, and he also looks around, does some tests, that's a good mechanic.
But if your mechanic says "ehh it could be this that this this....", you replace something and something more and it still doesn't fix the problem, then I have bad news for you...

 

[bugsymike]

In general I would agree with you and the principles you lay out have stood me in good stead of many years of servicing and repairs on a large variety of motor vehicles.
What I am noticing more recently is electrical error codes that point to a certain faulty component, however where in the past a multimeter could be used to test the Ohms and volts etc. at a plug, increasingly that information is either not available or an oscilloscope with correct wave forms patterns to compare with, which involve a large cost and annual subscription are required.
This means that diagnosis can be highly specialised, costly and in some cases not always diagnosed accurately by the so called specialist either.
For example I have a 2010 Doblo Maxi 1.6 multijet which brings up an error code P010F-21 which is described as Air Mass Meter (MAF sensor) sensitivity drift below lower limit, or on another diagnostic tool as Mass Volume Air Flow Sensor A B correlation.
It sometimes also shows error code P0113-15 higher voltage than expected from intake air temperature sensor. The sensor does both function MAF and IAT.
On a early 55 reg.1.9 Doblo with a similar MAF issue involving black smoke I was able to trace the fault using a simple Multimeter to probe the wires and traced it to a poor wiring plug, however on this later version a simple meter doesn't give the same voltage changes, so I am guessing a oscilloscope is required unless you can advise a simple test.
As retired now I cannot justify buying expensive diagnostics or subscription services.

 

[porta]

This is increasingly my problem with ‘plug n play’ diagnostics…it tells you you have a problem, no shlt sherlock! Whereas the original ‘blue’ book Fiat manuals, the red ‘specialist systems’ Fiat manuals and the later CD roms gave you values to check, with that indispensable AVO meter.
Now diagnosing seems to be, well it’s this code so could be this sensor, so we’ll replace that. Well that didn’t work, so let’s fit this actuator. Well that didn’t work, so let’s…ad-infinitum…
My dad, who was a ‘leading aircraft technician electrical’ RAF used to say, always presume the other guy is an idiot and start from the basics, positive/ground, fuse, bulb, connectors, wiring, continuity, then worry about the components!
One thing I have noticed, from many of the ‘cries for help’ posts, increasingly and frustratingly more recently, is those that have got, quite frankly, absolutely shoddy service from the dealerships themselves. I hasten to add, this isn’t restricted to Fiat or even Stelantis in general, but all the marques…do they just not care anymore?

 

[kakashi7593]

In general I would agree with you and the principles you lay out have stood me in good stead of many years of servicing and repairs on a large variety of motor vehicles.
What I am noticing more recently is electrical error codes that point to a certain faulty component, however where in the past a multimeter could be used to test the Ohms and volts etc. at a plug, increasingly that information is either not available or an oscilloscope with correct wave forms patterns to compare with, which involve a large cost and annual subscription are required.
This means that diagnosis can be highly specialised, costly and in some cases not always diagnosed accurately by the so called specialist either.
For example I have a 2010 Doblo Maxi 1.6 multijet which brings up an error code P010F-21 which is described as Air Mass Meter (MAF sensor) sensitivity drift below lower limit, or on another diagnostic tool as Mass Volume Air Flow Sensor A B correlation.
It sometimes also shows error code P0113-15 higher voltage than expected from intake air temperature sensor. The sensor does both function MAF and IAT.
On a early 55 reg.1.9 Doblo with a similar MAF issue involving black smoke I was able to trace the fault using a simple Multimeter to probe the wires and traced it to a poor wiring plug, however on this later version a simple meter doesn't give the same voltage changes, so I am guessing a oscilloscope is required unless you can advise a simple test.
As retired now I cannot justify buying expensive diagnostics or subscription services.

I will add, I was able to get an oscilloscope off Aliexpress for about 20$.(only thing I needed to do was assemble the case, easy peasy)
Also I was able to get my hands on one oscilloscope from 90s, bought it on flea market.

Even though someone can posses these tools, technician needs to know what values he is looking for to be able to tell if something is wrong.

When it comes to OBD2 diagnosis system inside a vehicle, I use it as a pointer, kind of like "hey problem is here somewhere close by, go investigate"

Reason for end users having soooo very little information available today is, they don't want you to repair your stuff.

Ever heard of Right to Repair movement ?

You used to get long ass manuals,books,schematics with values and all components listed down to a wire, back when technology was made for the sake of advancement.
Nowadays everything is just slimmer and more slick looking and they want you to own nothing while paying for subscriptions everywhere.

That's why its important for us, regular people, to write these things down, create our own database of information to reference later when we go diagnose a fault on our vehicles.
They, the manufacturers, wont help us, unless its them fixing it and you not looking.

 

[bugsymike]

As I understand it 90s Oscilloscopes are not suitable as analogue and modern cars need digital, plus the cheap basic scopes are sometimes only single channel or have other limitations such as the voltages that can be tested are not high enough for all automotive use, so it starts getting more expensive again.

 

[kakashi7593]

I don't think that is how oscilloscopes work.
To my understanding, analog oscilloscopes are called like that because they rely on analog technology to display the signal on screen, which is actually CTR. Changes on vertical and horizontal deflection plates(which are magnetic I believe) affect how beam moves across the screen.
There's a gun that fires the beam and it is being deflected by these plates.

Digital oscilloscopes use an internal computer to process and display signals in real-time.
Hence the screen is slim, LCD screen for example.

My 90s oscilloscope can measure 400 volts( I cant remember off the top of my head if its RMS or peak to peak or what exactly), and this cheap Aliexpress oscilloscope can do 50Vpp with a X1 probe, or 10 times that if you use X10 probe.
To my understanding, a car battery is 12 volts DC, so this should be plenty to display it on the screen.

I am not sure what waveforms do computers inside a car produce but here is one video where he explains some stuff


And here you can see he is looking at a signal of about 70 volts


Only reason, well two, why you might need an oscilloscope that is BATTERY powered, is so you don't fry your oscilloscope by shorting it, but this is main concern when dealing with AC mains power in our homes, not DC inside a car, or in fact anything that is floating
(Circuits connected to a grounded power source, like an electric wall outlet, will be electrically tied down and referenced to the Earth, which is abbreviated GND. Power sources that are not electrically connected to the Earth, like a battery, are referred to as floating sources.)

 

[bugsymike]

Thank you for your reply, I have watched the first video before, I believe he uses the quality Pico tools which although good, start to get more expensive and hard to justify if just using for small projects.Also to get the full benefit and back up you would need to go on their training course and sign up for update subscriptions etc. The other point is, he has to use an attenuator for some tests, much like you were saying a x1 or x10 probe etc. as although you may start with 12 volts on most cars and a lot of the time the ECU uses sensors at under 5volts there are some parts such as the diesel injectors that use around 80 volts to trigger them, this voltage supplied from ECU capacitors or similar. Plus of course on petrol engines the coil to fire the spark plugs can often be around 30 Kv so it is easy for a basic digital oscilloscope to then need more expensive add ons to do many of the tests.
The other video does show an interesting little scope, but the cheapest one on eBay seems to be around £170 from China, so I expect in the event of after sales problems might be tricky, apart from the claimed delivery times often expand to more than 28 days.
I have used a analogue scope on a large mains 240 volt powered Crypton Diagnostic tuner back in the 1970s at a car dealership, but in general terms on modern vehicles it wouldn't be of much practical use for most jobs I feel.