November Diagnostic Challenge (wrapped up)

[Jeremy airjer W]

This time I thought I would challenge you to the thought process behind a drive-ability diagnoses. I will give you the info and then lets see what you think should be the next steps into finding the solution. Different Techs will have different approaches but this is the process I used to figure this one out in about 30-45 minutes.

Vehicle:

2006 Chevrolet Silverado 2500HD 4WD with a 6.0 liter engine.

Symptom:

Vehicle was towed into the shop. Customer states that the vehicle cranks, starts, and immediately stalls.

Whats the first step?

[fishnowworknever]

check fuel pressure/fuel pump.

[Jeremy airjer W]

Nope

[Scott K]

Unplug the maf

[Jeremy airjer W]

Nope.

Where looking for the chronological order of how to progress with a diagnosis. We haven't even opened the hood yet, not that I would get that specific.

[dirtymike]

Perform a detailed patient history and orthopedic tests. That's how I arrive at my top three DDX's.

[Jeremy airjer W]

Perform a detailed patient history and orthopedic tests. That's how I arrive at my top three DDX's.

Closer!

[Macgyver55]

Vehicle:

2006 Chevrolet Silverado 2500HD 4WD with a 6.0 liter engine.

Symptom:

Vehicle was towed into the shop. Customer states that the vehicle cranks, starts, and immediately stalls.

Whats the first step?

First thing I always do is verify the symptom!

[Jeremy airjer W]

First thing I always do is verify the symptom!

Correct!

I turned the key to the run position, varified the computer would turn on the check engine light, say the guages and other lights fired up, and heard the fuel pump running. when i attempted to start the vehicle started and stayed running with the check engine light on the whole time. After about 5 to 10 seconds the vehicle stalled. The vehicle would then start and immediately stall. I did not know it at the time but the 5 to 10 seconds that it initially ran was a clue. You will see that when we have finally solved the issue.

So we variefied the customer complaint, What's the next step?

[Scott K]

Search for TSB, or SSM.

Grab scan tool, check for codes

[Scott K]

This would be my order of diagnostics. Receive RO from service writer, complain it is a GM, whine why I have to work on the GM. Get the keys, whine while walking back to get the vehicle that I have to work on a GM. Jump in vehicle, try to start, and verify concern. If it is nice outside, I will grab a scan tool, and retrieve codes. Then try to see if there is a sensor I can see that isnt reading correctly in the pid data. Growl again, because I am working on a GM. At this point, I would run an OASIS, to find out is there are any TSB's, or SSM's regarding the concern the vehicle has, or codes I pulled up from the scan tool. If it is cold outside, or raining, at this point I will whine to someone else, that I have to work on a GM, and that it sucks to be them, because they have to help me push this GM into my service bay. If it was nice outside, and I didnt need to lift the vehicle up, I would continue to look at it outside, maybe checking fuel pressure, or testing a certain sensor that may have tested out of spec. After diagnosing the vehicle, I would walk to the parts counter, whining that I need parts for a GM, then they would ask me why I am working on a GM, then I would say, no clue, I must have pi ssed off someone. Then a day later, install new part, test drive it to verify it is fixed. Hang up keys. Then give service writer grief about giving me a GM vehicle.

That would pretty much have been the procedure, in order that I would have taken.

[frabillfisher]

Sounds like possible security issue for the passlock sensor...install tech2 and check.for.codes

[JOHNBIGDOG]

This would be my order of diagnostics. Receive RO from service writer, complain it is a GM, whine why I have to work on the GM. Get the keys, whine while walking back to get the vehicle that I have to work on a GM. Jump in vehicle, try to start, and verify concern. If it is nice outside, I will grab a scan tool, and retrieve codes. Then try to see if there is a sensor I can see that isnt reading correctly in the pid data. Growl again, because I am working on a GM. At this point, I would run an OASIS, to find out is there are any TSB's, or SSM's regarding the concern the vehicle has, or codes I pulled up from the scan tool. If it is cold outside, or raining, at this point I will whine to someone else, that I have to work on a GM, and that it sucks to be them, because they have to help me push this GM into my service bay. If it was nice outside, and I didnt need to lift the vehicle up, I would continue to look at it outside, maybe checking fuel pressure, or testing a certain sensor that may have tested out of spec. After diagnosing the vehicle, I would walk to the parts counter, whining that I need parts for a GM, then they would ask me why I am working on a GM, then I would say, no clue, I must have pi ssed off someone. Then a day later, install new part, test drive it to verify it is fixed. Hang up keys. Then give service writer grief about giving me a GM vehicle.

That would pretty much have been the procedure, in order that I would have taken.

I loled at this because its the same thing anyone at our shop, including myself, would do.

Side note, you would find no tsbs/ssms using oasis, as it only works for Fords or not?!

Did the truck start and run "normally" for the 10 or so seconds and shut off abruptly? what is the dash telling you.

[jmd1]

does it have fuel in it

[Jeremy airjer W]

Yes the truck started normally and ran normally until it stalled. This is not a security issue or I would have mentioned it when I was verifying the customer complaint.

Grab scan tool, check for codes

Exactly! Since the check engine light was on why not scan for codes to see if there are some clues as to what is going on. There where several codes current and in history. I was not the first under the hood of this one and those of you in the business know when you get the feeling somebody has been under the hood that shouldn't be. Anyways the codes (sorry I don't recall them specifically) didn't seem to have any relationship to each other. I do remember there being a P0300 (random cylinder misfire), P0102 (low MAF frequency), and P0641 (5 volt reference incorrect).

Remember we are not "diagnosing" anything right now, we are looking for the next logical step in the diagnosis process.

What's the next step?

[Eric Wettschreck]

What's the next step?

Go to the bathroom.

[Jeremy airjer W]

Go to the bathroom.

Ain't nobody got time for that!

[JOHNBIGDOG]

Note all cm dtcs, clear and perform koeo, koer(lol) self tests for hard faults, check for relevent tsbs and ssms related to symptom and dtcs.

Also perform a visual inpection of under hood components.

[Jeremy airjer W]

Note all cm dtcs, clear and perform koeo, koer(lol) self tests for hard faults, check for relevent tsbs and ssms related to symptom and dtcs.

Also perform a visual inspection of under hood components.

Correct! Except for the under hood inspection, and the tab stuff. We don't even know what we are dealing with and are still working out the direction we need to go.

Remember our timeline so far is maybe ten minutes. Time to verify the complaint, check for codes, clear codes, try to start, and then check for any new codes.

Anytime there are multiple codes, say more than 4 or 5, that don't seem to have some correlation to each other, clear them. Then in this case I tried starting the vehicle a few times and then rechecked for codes. BINGO! P0641 comes back.

NOW, what's the next step?

[JOHNBIGDOG]

Forgot you mentioned it already.

Check the 5v reference voltage pid on scan tool. See if it reads high or low while crakning start looking for refrence voltage sensor problems.

[Jeremy airjer W]

Forgot you mentioned it already.

Check the 5v reference voltage pid on scan tool. See if it reads high or low while crakning start looking for refrence voltage sensor problems.

Nope!

No wonder why it takes you dealer guys a week to fix anything! LOL

Anybody else?

[Black_Bay]

Begin replacing electrical components, most expensive first, until the problem goes away.

[Jeremy airjer W]

Begin replacing electrical components, most expensive first, until the problem goes away.

I like the way you think! Although that might be SOP at the Washke Chev Im sure thats not the case whats his name at Vermilion auto! lol

[MikeG3Boat]

Since this thread has kind of stalled. What was your next step?

[Jeremy airjer W]

Since we now have a code we have a direction to work in. The next step is to research the code to see what it is trying to tell us.

In this case P0641 is a code generated when the computer sees a problem with the 5 volt reference signal to various sensors. After a little more digging we find that there are 4, 5 volt references from the PCM which are bused internally (the PCM generates a 5 volt reference that is split into 4 outputs). One wire goes to the A/C system, one wire goes to the fuel tank pressure sensor, one wire goes to the MAP sensor, and the last wire goes to the oil pressure sending unit.

Now we know that there is a problem with the 5 volt reference and we have narrowed down the possibilities to 6 (PCM, wiring, A/C system, MAP sensor, oil pressure sending unit, and/or the fuel tank pressure sensor.

What's the next step?