Thinking Like an Automotive Diagnostic Technician

Today we are looking a little deeper at the mind and process of a diagnostic technician. Right now I am in the process of training two new technicians, with a third starting soon. That means I am in full on teaching mode all day long. I really enjoy doing it. So I am trying to help develop these new tech's diagnostic process. That is something I also wanted to share with you guys. It is something that a lot of automotive techs really struggle with. It is not an easy thing to build. Then after you build it, you have to keep fine tuning it, and working it. Not only to get better, but to stay current.

Join me today as we step inside:

About the diagnostic process
Ways to think about diagnosing cars
Ways to get stuck diagnosing cars
How to get unstuck
K.I.S.S
Work easy to hard
Don't Assume
Scan tool loop
Getting more information
FUSES!
Write it down
and more

Humble Mechanic Podcasts

Failed VW parts videos

Tool Reviews

How To videos

MK1 VR6 Swap Videos

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GOOD STUFF ON AMAZON

[PHXGlock]

"You gotta go low tech before you go high tech" A factory tech specialist from Mercedes Benz told me this when I was an Apprentice. Some of the best advice ever.

[seriousmechanicing]

I'm in the fortunate situation where I get to diag 10-20 cars every day and this covers it pretty well. The only things I could add are to make sure you know how to use your service information as efficiently and thoroughly as you can, never assume anything that you haven't tested, and finally relax and have fun stress and anxiety make bad ideas and decisions seem good.

[papelyll]

I'm a diagnosis master technician Toyota, i work for cfao in African and i really like this videos, thank you for all

[dhitch]

I work as a military technician on humvee’s and other trucks. We had a humvee come in with a lighting issue. Turn the headlights on and all the lights, marker lights, turn signals, stop lights, and blackout lights(Lights for night driving with NVGs) except the headlights would come on.
Started with the switch checked pin to pin and everything was fine, checked the connector same thing everything was fine. Jumped the wiring from the connector to the headlights, and other lights one by one and they worked like they should.
After a good full day of checking continuity, powers, grounds, this and that and everything else I realized I was having to awkwardly twist the harness and connector for the light switch to plug it in. Looked at the pins on the connector and pins on the switch and found out the connector was twisted internally and all the pins were about 4 off so pin “a” on the connector was going to pin “d” on the switch.
Took the connector apart and put I back together the right way and presto we had headlights and everything working like it was supposed to

[Bennystafford]

Hey guys,
I had a P0420 code for several years.
At the time, and with my lack of knowledge, I didn’t care about the P0420 code …I thought it was only emissions. The code IS for emissions, but it can ALSO mean other problems exist too! I’ll explain later.
So I drove it like that for maybe 35k miles, maybe 40k.
A surprise pregnancy (no. 5) sent us over the baby seat limit for our larger ride. Lol
Alas, we had to buy a new car …and sell my faithful Altima (now at 201, 000). This made the P0420 code more of a deal breaker. I wouldn’t get as much with the engine light on.
And so began my journey to a CEL-free dash!
I started with Bluedriver. So glad I did!! I was able to see my fuel trims!!!! Life changing tool!!!
I was at 9% on my long trim and 17% on my short trim!! This meant I had a few leaks!
I was opened up to the world of not trusting CEL lights! Curse you Bluedriver!! Lol
I started with a starting-fluid-spray-test and found the first leak. Turns out when I had replaced my PCV valve, I had dropped a small ring gasket that sat in the PCV-hose-to-intake port. Fixed that and watched the STFT drop to 14%. Still not good enough. Read that a lot of Altimas have cracks in their exhaust header. Checked that and found TONS! TONS! There’s my problem!
Fortunately, the cracks and the P0420 code are the same part. My destiny was calling me! I had to replace the catalytic manifold to WIN! Lol
.
So I first tried a $100 aftermarket catalytic converter/exhaust manifold on Amazon. Didn’t even come close to fitting! Should have known.
Returned that and bought a $350 “OEM” one from O’Reilly’s. That didn’t fit too well either. Ugh!
Engine side heat shield didn’t fit, so I left that out. Had to modify a few heat shield holes for the radiator side.
Had to use spacers and different bolts to match the manifold mounting bracket up near the bottom. Finally got it in. What a pain!
Also found out that my exhaust pipe bracket had been squashed from coming down off a curb from our yard or something. So I replaced that and it helped the pipe meet up with the new manifold even more. Still wasn’t OEM though as O’Reilly said it was. Pshshh.
Anyways, so I started the car up.
P0420 gone! Boom. Within the first drive cycle! LTFT went down to 8%! So awesome! LTFT + STFT went to 9%. Nice!
.
Here’s where the crap hit the fan!
The dreaded P1273 started popping up to say hi. Ugh!
Went through a few fuel trim clearing procedures (including unplugging the battery overnight) and it just kept popping back up.
Tons of sites were saying it was a lean issue. Injectors, bad sensors, yada yada.
Tried replacing my sensors a few times. Both upstream and downstream! Nope. It came back.
.
Found on YouTube that ONE mechanic was saying this code also popped up from an EXHAUST LEAK after the flex hose joint. I had remembered that after I installed the new converter manifold that the flex joint just didn’t feel as nice of a fit when I had put it back together. It was tight, but just didn’t feel right.
So I looked at that while the car was running and sure enough, noticed that I could hear the engine when I put my ear up to the flex joint. There was a smaaaall gap where O2 could get in and throw the readings at the 2nd sensor! Not enough to notice a huge difference on my Bluedriver (2nd sensor was showing 0.265 volts), but enough to supposedly throw my P1273 code.
So I installed a few rings around the male pipe connector on the manifold to help lift the curved side of the flex pipe gasket out a little further to fill up that gap I was talking about. After a few rings that I had cut out of a tin sheet I was able to make it mesh good to work with the new manifold and old flex joint and pipe. Bolted it back up. Started the car. No more noise.
The car sounded better than it had in a long time! No cracks in the exhaust, no flex pipe leak!
Performed the fuel trim history clearing procedure.
Man oh man I can’t tell you how pleased I am!!!! LTFT is 7%! LTFT + STFT hovers from 7 to 9%!
Been driving the car now for a long time and no codes!!! No P0420, no P1273!
Engine purrs!

Here’s my final readings:
(range includes cold start to warm engine, at idle and 3000 RPM)
STFT 0 to 9%
LTFT 7%
O2B1 0.12 to 0.9V
O2B2 0.28 to 0.31V
So what did I learn? Here’s the main things that will change my mechanic life forever:
1. Catalytic converters should last for 200, 000+ miles with a well maintained engine. If you’re cat goes bad, you probably have other problems that just haven’t thrown a code yet.
2. You can have small problems with no CELs that can turn into big ones!
3. Fuel trims can really help diagnose issues!
4. The 2nd O2 sensor is not JUST used for exhaust emissions! The ECM uses BOTH O2 sensors to determine fuel trims (and lean or rich fuel conditions).

So what did this mean for me? That I will fix catalytic converter problems much sooner from now on if I plan to keep my car around past 200, 000 miles.
If your engine is running rich for a long time it can damage other parts, and eventually expensive ones. I’ll admit, emissions aren’t my biggest concern. But I do care about engine longevity.
All that said, if you have a P0420, P1273, or P1274, hopefully my story will help save you some hassle.
Take care,
Benny

[Sinkorswim]

I literally just started watching you’re videos today and I’m ready to be an entry level tech after about a year an a half of doing lube tech work. I am learning so much from watching you’re video and I really appreciate them and the effort that goes into them.

[coycarlson]

To properly test, diagnose and repair today’s vehicles - one really has to understand and be an electronic technician.
VERY GOOD ADVICE 👍✌️

[crob]

Thanks for putting driveway diagnostics videos up. It seems that with your video the only way crooked mechanics can rip people off is by NOT telling the customer whats really wrong with their car.

[GDoza]

Im glad this came up on my recommended tab, definitely opened up my mind of how i work on cars. 👍

[TyrekClayton]

I'm currently in automotive tech school and they're teaching us how to use scan tools to detect trouble codes in my emissions class and I love it well tbh I love everything car related but this is Gold to me

[mtabbert]

Your channel is great. I'm thinking of suggesting that my apprentice watch. You know, like "homework"!

[ncrdisabled]

I spent 7 years in the NAVY and was a reactor operator and all the hands on repair ways was always start at the end of the circuit and if it is not working cut in half and if it not working there you then cut it 1/2 again . With that mind set I got thu some very hard NAVY schools . 2 had a 45 % failure because they would not follow that way of repair . The NAVY wants it done there way as it has proven to work for them for years. I still use it today I an I was the navy in the late 80 s

[ScorpionRegent]

When checking fuses also check that it's the right amperage fuse for the circuit. There are people out there who don't understand the difference and will use any fuse that fits.

[professorjack]

There is something very rewarding about fixing that electrical issue no other "mechanic" in town could!

[andrewwilson]

Wise words. Sometimes the next step is a step back. Your initial observations are the most important and attention to detail at this stage can save so much time money frustration and effort. Great video mate.

[wojtekdobrowolski]

What got me many times was a low voltage/worn car battery. A VW Passat B6 sometimes did fire up and sometimes it did not or id did take too many tries, thought it was a steering wheel lock problem because it's apparently a common issue and has similar symptoms but it has to have been the starter motor solenoid not having enough current running through the coil to push the pinion all the way through to engage with the starter ring and close the circuit.

[andrewwilson]

The crazy thing these days is how the technology gap is changing. I trained as and spent twenty five years working as an avionics engineer . Modern vehicles are embodying technology that was the preserve of sophisticated military jets and helicopters! The technology gap is getting narrower all the time. We have cars with radar, thermal imaging, flir, head up displays etc! It feels like the car makers are in a technology arms race to utilise the most cutting edge technology available. They only going to get more complicated and tricky to work on. All I can see in the future is punishing bills for owners when glitches rear their heads. The repairs and maintenance on the aircraft shows just how much work is involved.

[mlb]

Same here about walking away, a simple task alows my brain to reboot and normally I get an idea where to go next, and boom problem found.

One thing I do is based on experience is testing most likely cause, if the both head lights do not work but high beams work and all other lights the easiest thing to do is put a bulb in:) built in test light;) unless bumber removal is required. A lot of techs have the issue of over thinking a problems.

As for modules confusing tech, BTDT tail lights go out on a later model dodge truck, but a bulb in and it still doesn't work, clear fault code in BCM and it works again. Lots of techs have gotten stuck on that simple issue.

[iLLBuddy]

Like the vids, man. First tip of the vid. Check fuses. Then you said you did all the basic checks and about to check the motor. Then the problem was a missing fuse...

[ericverster]

It's kind of embarrassing how many times I've been burned by a missing or blown fuse.