Diagnostic direction

Jasper from Fort Collins Technician Posted   Latest  
Question
Network Communications
2007 GMC Acadia SLT 3.6L (7) 6-spd (6T75)
Communication Loss
Low-Speed Bus

Greetings everybody! I'm excited to be a part of this community, and I'm hoping someone can give me a bit of direction in my testing. I'll try to be succinct, but if you would like more info please ask.

This 07 Acadia was brought in by a customer who was unsure if he should be visiting us or a priest, because he was convinced that it was possessed. The issue was that the gauges would drop to zero randomly, accompanied by loss of the radio, and I also found that the power windows and locks would be inoperative, and if you were to turn off the ignition while this was happening, there would be a no-crank condition.

Long story short, after some research and testing, I found the I/P fuse block full of the green death, replaced it, and symptoms improved. However, they have not completely subsided. It still experiences the gauge glitch, but now only for a second at a time, whereas before it would occur for several minutes, then resolve on its own, the reoccur again, and this was while driving or just idling in the bay. Now, it will only happen while driving, and is much more random. I feel like I've only made the diagnosis more difficult. So it goes.

Of course, there are U codes set in just about every module on the low-speed network after this glitch occurs, including airbag, bcm, door modules, hvac, ipc, liftgate, pps, radio, and seat module. The one code common to ALL of these is U0140: loss of comm with bcm. Does this point me towards trying to confirm a faulty bcm, or could any module on the network (or wiring between them) be bringing this comm line down? Should I start unplugging them one at a time to see when it resolves? Thanks in advance for any input!

0

Lane from Louisville

 

Mobile Technician
 

Does it have a sunroof? If so, check the drains. Also check the hvac case drain. I’ve seen water fill the battery box behind the passengers front seat. Also recently had one with water intrusion into SDM under passenger seat, backfeeding voltage and keeping the car alive with key out of ignition. Also had all the U codes you would want 😁

You found “green death”, that’s usually caused by moisture. Find the source first, that might lead you into a better direction. 

+2 Ð Bounty Awarded

Jasper from Fort Collins

 

Technician
 

Hi Lane, I did check those drains and they had already been sealed. I let the vehicle sit out in the rain overnight the other day and found no new leaks, but I'll keep looking for signs of water intrusion in other areas like under the seat.

Thanks!

0 Ð Bounty Awarded

Scott from Claremont

 

Manager
 

Hello Jasper,

FYI, please consider adding in the DTC's into the post via the Symptoms/DTC area. You have the entire J2012 database of DTC's with descriptions to choose from. See attachment. For OEM DTC's or symptoms not listed you can add your own.

My wife has a similar vehicle and one thing to be aware of on that chassis is that the windshield may have been replaced and improperly sealed which typically leads to the corrosive conditions you described. That vehicle being an 07, I think that were on the verge of seeing more and more intermittent network communication challenges and I look forward to discovering ways to identify and validate these through the use of tools and techniques surfaced through the collective effort of our community.

I look forward to seeing the resolution to your challenge.

Regards,

Scott

+8 Ð Bounty Awarded

Jasper from Fort Collins

 

Technician
 

Thanks Scott! Will do.

0 Ð Bounty Awarded

Jeff from Yakima

 

Diagnostician
 

Hi Jasper. Id want to look at the class 2 data line and see what the voltages are, Sounds like it has a class 2 data problem

+1 Ð Bounty Awarded

Adrean from Bakersfield

 

Diagnostician
 

Intermittents hate those . Might need the priest and a couple candles for this possed one .lol . I would start removing the splice pack jx205 or jx405 . or first with my scope monitor the low speed line and see what happens once the problems occurs . Then one by one disconnect each module from the splice pack . 

+1 Ð Bounty Awarded

Matthew from Lawrence

 

Technician
 

I would be worried about the connectors of the fuse box having poor connections . I'm sure you inspected them closing when replacing it but some Stabilant 22 on the connectors wouldn't be waste of time. I'd also want to check any module/connections in the I/P block/underdash area, like the BCM.

+1 Ð Bounty Awarded

Jasper from Fort Collins

 

Technician
 

Hi Matthew, I did my best to clean the I/p fuse block connections and ordered a new bottle of stabilant 22 just for this vehicle! Customer took it for the weekend, but I suspect it’ll be back soon.

0 Ð Bounty Awarded

Martin from Burnaby

 

Instructor
 

Hi Jasper. We just happen have an '07 Acadia in our program fleet on which the BCM failed following an errant unplug and re-connection of the BCM by a pair of students while chasing an installed communication concern on the high speed bus. (the BCM communicates on both Class 2 and HS GM LAN). These were the last of 7 pairs of students through the activity, on a vehicle that had been confirmed as starting and ran fine after every other group had diagnosed the failure. 

GM TSB #…E: Information on Body Control Module (BCM) Grounds - (May 20, 2013) GM SI document # 3444068 addresses the issue of BCM failure from a loss of power or ground to the BCM without battery disconnection. I strongly recommend reviewing the document and in particular Issue # 2, which can easily result in a BCM failure on that vehicle while performing diagnostics and not being aware of the required battery disconnect procedure, as in the case of my students. The listed symptom conditions plus a no crank were all present. 

Think of the related DTC that is common, as being yourself and a handful of buddies who hang out together. One day you don't show up for work and those buddies who always hang out with you, raise their hands to let the boss know that you didn't show up for work today with your SOH (State Of Health) clock in message, since you were not not there to sign in yourself. Your name happens to be U0140 (BCM).

Best practice will be to ensure that the BCM, B+, ground and ignition feeds are all present, to prevent any recurrence of a BCM failure. On the '07 Acadia that we experience the one and only ever failed module in the program, all of the system failure symptoms that you experienced were present and also the park and tail lamps were always on with the BCM connected.

So, in our case, I had the best pair of students diagnose the failure and then later in the day I performed the diagnostic tests myself and arrived at the same conclusion, that a BCM replacement was required (plus programming). They programmed the replacement module and the vehicle started.

However, a rather unusual symptom after the fact on this vehicle was that before the BCM failure, the engine had run fine on 6 cylinders, but following the BCM replacement it only ran on 5 cylinders. DTC P0315 was set for Crankshaft Position Variation Relearn not set, presumably caused during a voltage loss when the memory had been cleared. The relearn could not be performed and the end result was while the engine started, there was no CKP counter and that during subsequent diagnosis I found the CKP sensor signal to be very weak identifying the need for CKP sensor replacement. Oh what a fun location! After replacement and the relearn, the engine ran fine on all 6 cylinders. The students had exited the program by the time that I experienced and diagnosed these latter conditions, so it was down to me to diagnose and effect the repair. 

+3 Ð Bounty Awarded

Jasper from Fort Collins

 

Technician
 

Great info, Martin! Thanks for taking the time to post. I’ll be solving the issue as soon as it comes back.

0 Ð Bounty Awarded