Dash Warning Lights Acting Odd

My 2004 Envoy has 56k miles. It has had service previously (25k miles) for Service Engine Soon and Engine Reduced Power lights which resulted (I'm told) in updating the ECM software. At 50k miles the front HO2 sensor was replaced after posting a P0136 code .

Yesterday, while driving, all the dash warning lights turned on concurrently and stayed on. After pulling off the road and restarting the engine, all of them turned back off. Later in the day after a few restarts and about 60 miles, the ABS and Brakes warning lights turned on, then turned back off after 2 more restarts.

Today, the ABS and driver seat belt lights came on while driving. They both remained on after a restart. Releasing the drivers seat belt and relatching it had no effect on the seat belt light. When I returned home, the ABS light turned off in my driveway, I think when I put the transmission in park. After that, the seat belt light also turned off indicating the correct state of the latch and then accurately displayed the belt latch state.

Other than the odd warning light situations, the vehicle seems to drive totally normally. Currently there are no lights on, but I fully suspect more in the days to come.

Can anyone make any suggestions as to what is happening here? Thanks.

Welcome to AF, there is an extensive TSB concerning the possible source of this problem. Are you cpable of tracking down ground issues in the harness. If not get this to a dealer.

FYI, This AM it was ABS and Air Bag warnings. This afternoon, all lights were off.

As for the ability to track a ground, given a reasonably useful and accurate procedure, I should be able to do it. Being an ex GM electrical controls engineer, and having a lot of good instrumentation shouldn't hurt. I do have the 4 volume repair manual set, but they alone won't point me very clearly toward a bad ground.

Being past the 3 year warranty, I shudder at turning a dealer loose with a blank check on this.

Therefore, for starters, can you direct me to the TSB that you mentioned?

Thanks!

Ok, the access to the TSB I use is proprietary I will try and out line it for you, one is on the l/s of the engine block. The other is under the dash R/s in front of the console, ground junction 201, remove the lower dash carpeted cover , the ground wire must be removed and cleaned, the console may have to come out also, now, this causes the inst. cluster to blink on and off, may not be same as you describe.

Thanks for your continued interest. I will follow up on your prev post. But beforehand, I have to ask a couple of questions to satisfy my curiosity.

First, my experience with poor/intermittent grounds usually shows up as adding resistance to a circuit to either dim a light or cause it to flicker bright/dim or on/off. In my case, my warning lights never flicker or dim. They are either fully on or fully off, and further, they never seem to change state unless the engine is restarted or when the initial warmup software timeout occurs, i.e. under ecm control. If my problem was a poor ground, it seems to me that I would see some dimming sometime, or perhaps some effect if I hit a hard road bump or something.

Second, my experience in most control circuits is that they use NPN type semiconductors with one side of the load (light in this case) connected to battery + and the other to the NPN switch to ground. This would mean that if I had a poor [open] ground, the light would never come on or at best come on dim. Again, I have never seen that symptom.

Finally FYI, I have never seen any lights fail the visual self test cycling that occurs at startup. Every one turns on concurrently. My problem is that one or more may not turn off...

Your thoughts?
Thanks.

Based on the nomenclature in the TSB, the symptoms, as I said are somewhat different. But this is step one to pin it down, it is possible the cluster itself is bad, that has been an issue, so has the ign switch, both of these cause either all lites flicker or no gages at all.