1995 Buick Lesabre P0341....Check my work.

[clinebarger]

Car came in on Thursday for a CEL/MIL diagnostic, 81,000 miles & super clean other than some trans leaks & a oil pan leak which I noted on the repair order.

L-Code 3.8L/4T60

History Codes...
P0341 Cam/Crank Error
P0342 Cam Signal Circuit
P1406 EGR Pintle Position Error

Hard Code...
P0341 Cam/Crank Error

This car is NOT OBD-2, Nor is it OBD-1, I've always called them OBD-1.5, It has a OBD-2 data link connector & alphanumeric generic trouble codes.....But little else in common with true '96 & up OBD-2 vehicles.

P0341 sets "hard" with closed loop fueling control enable, Clears with each key cycle, Saved in history/memory, Normal with OBD-1.5.

The first thing I did was pull the alternator & check the Cam/Crank sensor harness branches for rotted wire insulation from oil contamination. Nothing found.....Harness in fantastic shape!! Re-taped the harness/conduit with TESA underhood tape.

During harness inspection.....Cam & Crank sensors have been replaced recently, Looks to be Standard/Wells/BWD replacement junk?

*Looked over the trouble tree for P0341, Came to the conclusion that the ICM sends a Cam & Crank signal to the PCM & P0341 sets if one of these signals are missing or intermittent.

*Cam/Crank Error "Count" increases steadily as the engine idles, Has a slight "hitch" every now & again at idle.....My theory is it's losing #1 cylinder location & the PCM is switching back & forth from sequential injector operation to batch fire.

*Using my Vantage Pro in dual graphing meter mode.....I back-probed pin RB8 & RB9 at the PCM connector. Good clean 5 volt square wave patterns on both circuits. Recorded over 800 1-second frames while wiggling the harnesses & cam/crank connectors with NO drop-out in either signal.

*I also did a "tap-test" on the PCM.....Along with "Flexing" the PCM connector, Results were inconclusive as the error count steadily increases no matter what & the Hitch/stubble is erratic.

*Performed a "Drag Test" on PCM terminal pins RB8 & RB9, Both have GOOD drag on them.

I came to the conclusion that the PCM is either faulty or has a cracked solder joint.


The DRAMA filled part of this diagnostic
My shop foreman/service writer disagrees & thinks its a sensor or wiring issue. He doesn't believe in scope patterns & thinks that I should follow the trouble tree to the letter.

I tried to explain to him that I AM using a voltmeter on BOTH circuits, The ONLY deviation I made from the trouble tree was.....The engine is running while I performed the wiggle tests & I can see & record the actual patterns.

We had a heated argument that I wouldn't be able to paraphrase on the board. I RARELY cull a PCM as being faulty & I understand his position in the company as it pertains to NOT allowing technicians to throw parts at a vehicle on the customers or the companies dime.

 

[clinebarger]

The FUEL CONTROL circuit carries a 6X signal that is replicated by the ICM.
The CAM SIGNAL is the exact 1X pattern the Cam Sensor puts out....But passes through the ICM.

 

[Trav]

I had one this vintage doing this, it was a loose connection in the ICM plug, I forget which pin it was exactly as it was over 15 years ago.

 

[BigD1]

This is a head scratcher.

Is it doing it cold?

Standard/Wells/BWD quality has gone downhill over the years. I just replaced a third idle speed control motor over a 20 month period just the other day on the same car. Luckily, I paid extra, and bought BWD with lifetime warranty. Got it exchanged no problem, and was up and running within 15 minutes.

 

[kc8adu]

i would not be surprised if its a cracked joint in the pcm.
i have repaired a bunch of them.
joints crack at j leaded chips.
look for ragged erratic injector pulses.
also stalling where it starts back up easily.
if cam/ crank signals are clean on pcm input its either the icm or the pcm.
did you look at icm coil drive?

 

[CT8]

Been out of the Business 20 years, some stuff is fun and others is why it is called work.Seems you are doing great diagnosis. Off topic there is nothing like doing the work for a living to learn it! Is rather intense at times.

 

[clinebarger]

Originally Posted By: Trav
I had one this vintage doing this, it was a loose connection in the ICM plug, I forget which pin it was exactly as it was over 15 years ago.


Originally Posted By: kc8adu
i would not be surprised if its a cracked joint in the pcm.
i have repaired a bunch of them.
joints crack at j leaded chips.
look for ragged erratic injector pulses.
also stalling where it starts back up easily.
if cam/ crank signals are clean on pcm input its either the icm or the pcm.
did you look at icm coil drive?


Never stalls, In fact it runs great on the road/under load. Just the random hitch at idle & the resistant P0341.

I did monitor injector drivers on #1 & #6. And IT IS switching back & forth from sequential to batch at random & lines-up with the hitch.
I can't correlate it to the Cam/Crank Error counter....The scan data sampling/update rate of this PCM is like using dial-up internet. Though it might be the scan tool I'm using (Snap-on Solus Ultra).....I have a GM Tech 2 at home that I keep forgetting.

I also performed a "drag test" on all the pins at the ICM. I thought about installing a known good ICM.....However I hate having to rely on swapping parts to find faults.
The wiggle test I already performed "should" have found a bad connection at the ICM connector but I AM willing to see this through!!!!

Both of you mention the ICM, I don't see it being the ICM if I have good Cam & Replicated Crank signals at the PCM?? Would either of you like to expand on this?


I don't usually whine.....But [censored], Why couldn't they include a Cam & Crank PID in the data stream??

 

[Trav]

Going by memory this one didn't die either just a little unsteady idle sometimes. What I did was remove the connector from the ICM and used a small pick to crimp the round female terminals a little tighter, no more problem.

Not saying this is the case with this one just throwing out a similar case and the solution that cured it. I want to say it was an intermittent sensor ground, not a total fail just a wonky contact.
I am curious to see where this goes.

 

[clinebarger]

Originally Posted By: Trav
Going by memory this one didn't die either just a little unsteady idle sometimes. What I did was remove the connector from the ICM and used a small pick to crimp the round female terminals a little tighter, no more problem.

Not saying this is the case with this one just throwing out a similar case and the solution that cured it. I want to say it was an intermittent sensor ground, not a total fail just a wonky contact.
I am curious to see where this goes.


Thanks Trav!

Very interesting.....In the diagram it shows the Reference Ground as an "OUT" at the ICM along with the ground symbol. The way I read this.....The ICM is supplying the PCM with a Reference Ground?

 

[Trav]

It looks that way RB7 to pin L (253). The other thing is these ICM are grounded on the mount, corrosion on the bottom can be an issue with them.
It couldn't hurt to clean it and the iron mounting pad off and put some new heat sink compound on the bottom of the ICM.

It may be all for nothing but with something like this as you know can mean going down a lot of rabbit holes especially with OBD 1 and old systems.

 

[mk378]

Throwing the code even without the engine turning does suggest it's a problem with the link between the ICM and the PCM. Likely the PCM is looking for a certain DC level or pulse code from the ICM and not finding it.

 

[clinebarger]

Thanks again Trav......I removed the ICM & the face of the mount was like new (Garaged Texas car). I also removed the covers on the PCM & closely inspected the board with a magnifying glass....No cold/cracked joints that I could see.

Shop foreman finally sent the PCM off to be repaired only to get it back......And it still sets P0341.....Insert a string of swear words HERE!!!!! I clearly wrote on the PCM in sharpie that it was setting P0341 & all external signals & circuits check-out.
Without saying anything to the SF, I called the place that "rebuilt" it.....They couldn't (Or should I say wouldn't) tell me what they repaired or if they repaired/replaced anything at all.

Being pretty confident of my diagnosis....I called one of my contacts at (American Auto Salvage) & he had a 1995 Regal that just came in. Stopped by after work & the PCM had the same service number, Bought it for $50.

Swapped out the PROM's as they had different Calibration numbers.....FIXED!!!!!!!

Shop Foreman is steaming mad because I made an "Unauthorized Purchase" & we're going to have a sit down with the owner to "straighten" this out before I can get reimbursed for the PCM.