Intermittent Serial Data Problem

[axekick]

I'm back from a long time ago! I bought an 05 Suburban to fix up but I may be in over my head. I've learned a bit about this system since I got the truck home but apparently some module is interrupting communication through the class B serial data system. Most of the time, the gauges are all zeroed out except for speedo and tach. When it's like that, the shift indicator does not underline the current gear. Also when it's like that, dome lights don't work, auto door lock doesn't work, etc. etc.

It's my understanding that all of the modules communicate through one wire and if one shorts out or malfunctions it can throw off the whole system. I don't have a scanner that can give me module status but I do have HPTuners. during the times when the gauges are working, I can read/write with my tuner. When the gauges are malfunctioning I can't connect. So I have plugged in my scanner and started unplugging modules to see if it lets me connect and so far disconnecting the ones I've tried has not made a difference. So I think I've ruled out the BCM, gauge cluster, HVAC, Transfer case, Radio, and maybe the ABS, although when I messed with that one the gauges worked for just long enough that I thought I might have solved it.

From what I've seen around here, it looks like there might be an expert on this system that can help me diagnose the problem. If I have to, I'll pull the entire interior and check every module and ground and look for any shorts along the harness. In the worst case I think I could get something like this: https://currentperformance.com/shop/nbs-99-07-silverado-sierra-suburban-tahoe-integration-harness/ which appears to replace the whole body harness.

Does anyone have any obvious or not so obvious things to check?

 

[Fless]

WAG: remove the two connectors from the ECU (left front of engine compartment) and check for water migration, pin fitment, etc. Those gaskets can leak and cause issues. Not sure if that's a cause but something to check.

 

[axekick]

When I bought the truck it wouldn't start and I couldn't connect with my HPTuners. I pulled the PCM and flashed it with VATS deleted. I didn't notice anything weird there, but I bet that is the kind of problem I'm having. There is also a parasitic power draw that will kill the battery if it sits for a few days.

 

[S33k3r]

Here is a thread on a similar topic:

Parasitic draw with modules out

And this is a YouTube video on fixing parasitic draw.
QUADRASTEER! GM Parasitic Battery Drain from the FACTORY? (Part 2)
(Ignore the fact that it is for a quadrasteer. It applies to pretty much any GMT800)

Other YouTube Videos:
Silverado battery drain FIX
The BEST Way TO Perform a Parasitic Draw Test

I suggest doing some additional searches here (TYF) on "parasitic". There are a few threads floating around.
I also suggest the same on YouTube.

The information I provided was just part of a quick search. I don't like to just shout at people "do your own searches". I had that done to me before and I hate it. So I usually do a quick search, post results, and then suggest search better than me for more results. Good luck! And don't give up!!!

 

[Fless]

Here is a thread on a similar topic:

Parasitic draw with modules out

And this is a YouTube video on fixing parasitic draw.
QUADRASTEER! GM Parasitic Battery Drain from the FACTORY? (Part 2)
(Ignore the fact that it is for a quadrasteer. It applies to pretty much any GMT800)

Other YouTube Videos:
Silverado battery drain FIX
The BEST Way TO Perform a Parasitic Draw Test

I suggest doing some additional searches here (TYF) on "parasitic". There are a few threads floating around.
I also suggest the same on YouTube.

The information I provided was just part of a quick search. I don't like to just shout at people "do your own searches". I had that done to me before and I hate it. So I usually do a quick search, post results, and then suggest search better than me for more results. Good luck! And don't give up!!!

Be careful on that Quadrasteer video -- Ivan didn't know about the long "sleep" time on the HVAC module. I emailed him after I saw that. I've attached the TSB that states the AUTO HVAC module can take a loooong time to go to sleep.

It's also in this thread: https://www.tahoeyukonforum.com/thr...dead-then-battery-drained.151854/post-1935027

 

[axekick]

Here is a thread on a similar topic:

Parasitic draw with modules out

And this is a YouTube video on fixing parasitic draw.
QUADRASTEER! GM Parasitic Battery Drain from the FACTORY? (Part 2)
(Ignore the fact that it is for a quadrasteer. It applies to pretty much any GMT800)

Other YouTube Videos:
Silverado battery drain FIX
The BEST Way TO Perform a Parasitic Draw Test

I suggest doing some additional searches here (TYF) on "parasitic". There are a few threads floating around.
I also suggest the same on YouTube.

The information I provided was just part of a quick search. I don't like to just shout at people "do your own searches". I had that done to me before and I hate it. So I usually do a quick search, post results, and then suggest search better than me for more results. Good luck! And don't give up!!!

I appreciate that. It's helpful. I've actually learned a lot about the whole Class 2 Serial system from searching youtube. I have been tuning these trucks since 2009 or 2010 but I never had to learn about this system. Everything just always worked. These trucks are getting old now, though.

 

[S33k3r]

When you figure it out, please let us know what you found. I guarantee it will help others that come after you.

 

[axekick]

I absolutely will. I’ll be active here again now that I got this old truck. This forum seems to have held up well over the years. I got a lot of help here.

 

[TJ Baker]

I absolutely will. I’ll be active here again now that I got this old truck. This forum seems to have held up well over the years. I got a lot of help here.

Any chance you own one of those inexpensive Bluetooth (or WiFi) OBD2 adapters? You can actually do a crapload of useful stuff with those IF you know how or have some guidance.

I have spent an absurd amount of time studying all sorts of SAE J1850 VPW serial data stuff. Mostly on my 02 TrailBlazer but also my 05 Yukon.

I have a few threads over at GMTNation.com that deal with serial data and using these inexpensive OBD2 adapters.

 

[axekick]

Any chance you own one of those inexpensive Bluetooth (or WiFi) OBD2 adapters? You can actually do a crapload of useful stuff with those IF you know how or have some guidance.

I have spent an absurd amount of time studying all sorts of SAE J1850 VPW serial data stuff. Mostly on my 02 TrailBlazer but also my 05 Yukon.

I have a few threads over at GMTNation.com that deal with serial data and using these inexpensive OBD2 adapters.

No, but I just borrowed a scanner that might be able to help. It's not bidirectional and I can't start working on the truck until next week, but from all the different ideas I've seen I'm feeling confident that I'll be able to track it down. The fact that there is a power draw might actually help.

 

[Fless]

For a parasitic draw I would suggest NOT jumping to the "pull the fuse" method. The small fuses have test points on top of them and the voltage drop can be measured when there is current draw. Powerprobe's web site has conversion charts that will estimate the actual amp draw based on the fuse size and voltage drop. https://www.powerprobe.com/na/en/download-list

Pulling fuses, then reinserting them can wake modules that were previously asleep, making for a nightmare when testing. South Main Auto has a few, and others are available.

There are many good YouTube videos on efficient testing methods for parasitic draw.

 

[TJ Baker]

No, but I just borrowed a scanner that might be able to help. It's not bidirectional and I can't start working on the truck until next week, but from all the different ideas I've seen I'm feeling confident that I'll be able to track it down. The fact that there is a power draw might actually help.

Well, feel free to give a shout out if you need.

Here's a little look at the sort of stuff I do with a $15 OBD2 adapter..

This is what J1850VPW serial data actually looks like.
Ever heard of SOH (state of health) messages?
There's at least 10 or more of them here among the normal chatter in this screenshot.

Line 1: BCM sends bus wake up message
Line 2: BCM announces current Power Mode
Line 3: PCM announces the position of the transmission range selector.
Line 4: PCM announces engine is not running
Line 5: PCM sends SOH message
Line 6: IPC sends SOH message
Line 7: IPC acknowledges Transmission Range selection
Line 8: Onstar module sends SOH message
Line 9: RCC module requests current Power Mode
Line 10: BCM sends SOH message
Yada, Yada, Yada......

 

[BigDogYJ]

are you certain it’s a loss of data issue? Have you confirmed powers and grounds for ecm/pcm and bcm? Key grounding points are below driver headlight behind bumper is where ecm is grounded. And under dash cover at bottom of a pillar up against the windshield is where the bcm is grounded.

I only mention it because I started tracking what I thought was a class 2 issue years ago only to find I had an intermittent ground that solved the problem.

 

[axekick]

I was out of town over the weekend and got the flu so I've been man down all week, but you guys have given me so much to start with. Hopefully I can find some time to dig into this. The ECM is working fine. I have diagrams with all of the grounds and module locations. I'll start with the voltage drop across fuses and cleaning every ground I can find. I'll update when I get to work on it.

 

[axekick]

I have some updates as I get this thing working. Another problem I was having was not being able to put fuel in the tank. It would just click. It would take half an hour to fill it up. I went ahead and dropped the tank, took the whole cluster of evap lines off and just shook out all the carbon pieces, I replaced the charcoal canister and put it back together and took it to the gas station and filled it right up. So that's a success.

I also took the cluster to a local module/cluster rebuild guy. He called and said the cluster is corrupt and can't be rebuilt. He couldn't even pull the mileage info from it. So he sold me another cluster programmed to math my truck. I went ahead and paid to upgrade to one with a trans temp gauge. I have to go get it at lunch. I'll update how it goes. I do not think that's going to completely fix the class 2 problems but it definitely wasn't helping. I guess each thing I get solved will make it easier to find the remaining problems.

 

[axekick]

Another update, the new cluster seems to work perfectly! I think now if I can get all the check engine codes figured out I'll be able to get it inspected and registered.

As for that, I knew I had a weak cylinder. When disabling one injector at a time, the one that barely made a difference was cylinder 8 so I've assumed it was the problem. However, there was a code for a bad #1 coil and misfire codes. So before I drove to get the cluster I swapped the #1 and #3 coil. The code moved with the coil! So that's good news. I have some coils at my X wife's house and I have to go there tonight. I might actually have this thing running pretty good soon!

I still think there's a break in the class 2 data sometimes. I'll check the grounds BigDogYJ mentioned asap. but it doesn't really seem to be causing any problems with the gauges anymore and my scanner works most of the time and just loses connection occasionally. This project is coming along nicely, I think.

 

[axekick]

I still have some digging to do. The serial data still gets lost and comes back sometimes when I go over a small bump or accelerate. Speaking of accelerating, I swapped the bad coils with some extras I had. Then I kept having a misfire. So I popped the hood and one plug wire was off. I couldn't believe I left it off so I put it back on and drove. It was STILL missing. So I popped the hood and the plug wire was off again! Then I realized it was getting caught on the little clip on the steering shaft and pulling it off. Finally I routed it away from the steering and Voila! It runs smooth as butter. The serial data was working well so I took it out and tuned it. It feels healthy! I'm going to love this truck!

This morning, the serial data was intermittent on the way to work. I'll have to find time to keep diagnosing that. I will be a happy dude when I figure it out and get it fixed. I'm leaning toward a problem with the ABS module or a door module. There's one for the lift gate, right?

 

[axekick]

are you certain it’s a loss of data issue? Have you confirmed powers and grounds for ecm/pcm and bcm? Key grounding points are below driver headlight behind bumper is where ecm is grounded. And under dash cover at bottom of a pillar up against the windshield is where the bcm is grounded.

I only mention it because I started tracking what I thought was a class 2 issue years ago only to find I had an intermittent ground that solved the problem.

Can you tell me how to access the ground in the dash you're talking about? Remove the top dash cover?

 

[axekick]

I finally fished the two splice packs out under the dash to try to isolate the problem while there was a loss of communication. However, removing the comb from either one of them had no affect. I expected data to return to the cluster as soon as I unplugged it. I suspect a bad ground. Hard acceleration and bumps seem to cause data to flow or be interrupted. Also, one time I had the back hatch open and I threw my tool bag in there and the lights came on like it caused the data to return. I need to find grounds and modules in the back to check.

My engine has a knock sensor code and the oil pressure sensor seems to be not working, so as soon as I can get a set of knock sensors I'll pull the intake and swap those. While I'm in there I'll replace the valley cover gasket, Intake manifold gaskets, valve cover gaskets, oil pressure sensor and check and clean or repair the two grounds on the back of the block.

 

[Tonyrodz]

I finally fished the two splice packs out under the dash to try to isolate the problem while there was a loss of communication. However, removing the comb from either one of them had no affect. I expected data to return to the cluster as soon as I unplugged it. I suspect a bad ground. Hard acceleration and bumps seem to cause data to flow or be interrupted. Also, one time I had the back hatch open and I threw my tool bag in there and the lights came on like it caused the data to return. I need to find grounds and modules in the back to check.

My engine has a knock sensor code and the oil pressure sensor seems to be not working, so as soon as I can get a set of knock sensors I'll pull the intake and swap those. While I'm in there I'll replace the valley cover gasket, Intake manifold gaskets, valve cover gaskets, oil pressure sensor and check and clean or repair the two grounds on the back of the block.

Be sure to use an OEM oil pressure sensor and good quality knock sensors. You don't want to do that job twice. You also might want to get a new knock sensors harness. They're pretty cheap--so why not.