Multiple Issues

[SpaceFrank]

The G8 has been sitting for several months while I got around to swapping the radiator after cracking the upper hose barb. I started it up a couple of times to move it around, but haven't driven it until last weekend after I put in the new radiator. It had a couple weird intermittent issues before, but they seem to have gotten worse while sitting. Random ABS fault on engine start that goes away after a few seconds, door locks occasionally disengage/reengage (usually when driving over a bump or hitting the brakes), and worst of all it immediately dies when shifted into reverse (this had never happened previously).

Months before I stopped driving the car, the transmission would occasionally go into limp mode, cycling the door locks and locking itself in 3rd before eventually resuming normal operation. This seemed to be getting more frequent until it randomly just stopped happening. It isn't doing that now, either. I am running a custom tune from Pat Guerra, but that's not really new. I changed my transmission fluid about a year ago as a precautionary measure based on some other transmission-related funnies, but the fluid came out looking pretty clean and a sample was verified to be in good shape by Blackstone Labs.

So my guess is a bad ground somewhere, a bad harness connection, or possibly a TCM or BCM going out. I'm not even sure where to start looking. What should I check first?

[STL_G8GT]

The G8 has been sitting for several months while I got around to swapping the radiator after cracking the upper hose barb. I started it up a couple of times to move it around, but haven't driven it until last weekend after I put in the new radiator. It had a couple weird intermittent issues before, but they seem to have gotten worse while sitting. Random ABS fault on engine start that goes away after a few seconds, door locks occasionally disengage/reengage (usually when driving over a bump or hitting the brakes), and worst of all it immediately dies when shifted into reverse (this had never happened previously).

Months before I stopped driving the car, the transmission would occasionally go into limp mode, cycling the door locks and locking itself in 3rd before eventually resuming normal operation. This seemed to be getting more frequent until it randomly just stopped happening. It isn't doing that now, either. I am running a custom tune from Pat Guerra, but that's not really new. I changed my transmission fluid about a year ago as a precautionary measure based on some other transmission-related funnies, but the fluid came out looking pretty clean and a sample was verified to be in good shape by Blackstone Labs.

So my guess is a bad ground somewhere, a bad harness connection, or possibly a TCM or BCM going out. I'm not even sure where to start looking. What should I check first?

Are you sure the battery is in good condition?

[SpaceFrank]

The battery is only about a year old, and it's a premium AGM type from NAPA. It was pretty low after sitting for so long, but it did successfully start the car. Leaving it plugged into a battery charger until full didn't make a difference in the symptoms.

A buddy and I screwed around diagnosing it a bunch yesterday. We were able to get it to go into reverse after shifting it back and forth between neutral and drive several times. The first time we shifted it into reverse the engine didn't die, but the dome lights flickered (I don't recall if the RPMs dropped). After reading a bunch online about the 6L80E, I think it's pretty likely one of the shift solenoids is sticking or otherwise on its way out. We just about had ourselves convinced a bad TCM could be causing the other problems until we did some more test driving.

The engine runs great, and the transmission shifts through the gears just fine, but something screwy happens any time you hit a bump or slam on the brakes. The door locks cycle on basically any bump in the road, but worse bumps cause other issues: the AC stops blowing cold (or stops blowing at all), the gauges all die, the transmission shifts into neutral, or worst-case, the engine dies. As long as the engine stays running, all the other problems typically clear themselves after a few seconds (or more like a minute, in the case of the AC not blowing cold).

We left the engine running and started poking around the fuse box/power center under the hood, as well as the ECM and any harness connectors we could reach. No amount of jostling anywhere caused issues like we saw when driving. We killed the engine and took the fuse box apart, checking the big harness connectors on the underside; everything looked fine, and we put it back together. Test drove some more and had all the same issues. Finally on a whim, my buddy wiggles the ignition key while I'm driving, and everything I listed above happens. The engine stays running but door locks cycle, AC and dash electronics die. We pull the car over and leave it running. Wiggle the ignition key again; it all happens again. We didn't turn the key out of the run position, just wiggled it around. We tried to repeat this several times, and while it doesn't always happen, it definitely happened a few times. It should be noted that none of these issues have happened with the car stopped otherwise.

Just to see if the ignition key recall had anything to do with it, I took the ignition key off my key ring and drive around some more with just the bare flip key. Still got the same issues driving over bumps, so the extra weight on the key doesn't seem to have much effect. It seems more like an issue with the ignition switch itself.

Anybody else ever have problems like this? Is the ignition switch known to be a problem in these cars?

[STL_G8GT]

The battery is only about a year old, and it's a premium AGM type from NAPA. It was pretty low after sitting for so long, but it did successfully start the car. Leaving it plugged into a battery charger until full didn't make a difference in the symptoms.

A buddy and I screwed around diagnosing it a bunch yesterday. We were able to get it to go into reverse after shifting it back and forth between neutral and drive several times. The first time we shifted it into reverse the engine didn't die, but the dome lights flickered (I don't recall if the RPMs dropped). After reading a bunch online about the 6L80E, I think it's pretty likely one of the shift solenoids is sticking or otherwise on its way out. We just about had ourselves convinced a bad TCM could be causing the other problems until we did some more test driving.

The engine runs great, and the transmission shifts through the gears just fine, but something screwy happens any time you hit a bump or slam on the brakes. The door locks cycle on basically any bump in the road, but worse bumps cause other issues: the AC stops blowing cold (or stops blowing at all), the gauges all die, the transmission shifts into neutral, or worst-case, the engine dies. As long as the engine stays running, all the other problems typically clear themselves after a few seconds (or more like a minute, in the case of the AC not blowing cold).

We left the engine running and started poking around the fuse box/power center under the hood, as well as the ECM and any harness connectors we could reach. No amount of jostling anywhere caused issues like we saw when driving. We killed the engine and took the fuse box apart, checking the big harness connectors on the underside; everything looked fine, and we put it back together. Test drove some more and had all the same issues. Finally on a whim, my buddy wiggles the ignition key while I'm driving, and everything I listed above happens. The engine stays running but door locks cycle, AC and dash electronics die. We pull the car over and leave it running. Wiggle the ignition key again; it all happens again. We didn't turn the key out of the run position, just wiggled it around. We tried to repeat this several times, and while it doesn't always happen, it definitely happened a few times. It should be noted that none of these issues have happened with the car stopped otherwise.

Just to see if the ignition key recall had anything to do with it, I took the ignition key off my key ring and drive around some more with just the bare flip key. Still got the same issues driving over bumps, so the extra weight on the key doesn't seem to have much effect. It seems more like an issue with the ignition switch itself.

Anybody else ever have problems like this? Is the ignition switch known to be a problem in these cars?

Have not seen a faulty ignition switch just yet, but awesome that you ran it down.

I wonder if it's something as simple as a bad connection at the side of the barrel/harness as opposed to being internal to the switch.

On the other hand, your symptoms seem to be the first parts of why the recall was initiated for the barrel/key... Although I think it was more about it fully rotating out of the run position with stuff hanging. I wonder if what you've come up on is part of the same problem.

[SpaceFrank]

Yeah, I'm thinking of taking it to a good dealership for the recall and telling them about the other problems at the same time. I've never heard anything about the recall replacing the switch, but maybe it's related. I've never had issues with the key rotating out of the run position.

[SpaceFrank]

After talking to a dealership, apparently the recall work is done without even touching the car. They just cut a new key and put your chip in the new fob. So there'd be no benefit to taking it in for the recall work since I'd still have to pay for any diagnosis.

I did a little more test driving yesterday. Tried using my older key as well, just to eliminate the key as the issue. I saw the same issue with both keys, so no such luck.

However, the last time I saw a hiccup in the dash and AC when going over a bump, I got something new: a message in the DIC saying "Engine Immobilized. Check Manual" (or something similar). The engine stayed running, and I drove back home and turned the key off and back on without removing it. The "Engine Immobilized" message remained, but it still let me start the car. I'm not sure if the "immobilization" just doesn't work as intended, or if my custom ECM tune is affecting it in some way. I turned the car off again and actually removed the key, and after that the message was gone and the engine continued to start with no problem.

I'm no more an expert on the anti-theft system than I am on the rest of this car's electronics; I've started searching old forum posts, but I haven't found anything quite like these symptoms and I've got a lot more to read. There are just too many possibilities. Is the anti-theft system the root of my problems, or is it just another symptom from everything being jostled so many times?

[G8eraid]

Have you tried reprogramming the key fobs, it may be worth a shot if not...
Since the issue is intermittent and only happens when the cylinder moves(car jolted going over bump etc.) I would think it is probably an issue with the part that picks up the chips frequency inside the fob. Not sure where its located exactly (cylinder, behind knee bolster or dash). Will try to locate some schematics and post them up here


Sent from my Nexus 6 using Tapatalk

[STL_G8GT]

After talking to a dealership, apparently the recall work is done without even touching the car. They just cut a new key and put your chip in the new fob. So there'd be no benefit to taking it in for the recall work since I'd still have to pay for any diagnosis.

I did a little more test driving yesterday. Tried using my older key as well, just to eliminate the key as the issue. I saw the same issue with both keys, so no such luck.

However, the last time I saw a hiccup in the dash and AC when going over a bump, I got something new: a message in the DIC saying "Engine Immobilized. Check Manual" (or something similar). The engine stayed running, and I drove back home and turned the key off and back on without removing it. The "Engine Immobilized" message remained, but it still let me start the car. I'm not sure if the "immobilization" just doesn't work as intended, or if my custom ECM tune is affecting it in some way. I turned the car off again and actually removed the key, and after that the message was gone and the engine continued to start with no problem.

I'm no more an expert on the anti-theft system than I am on the rest of this car's electronics; I've started searching old forum posts, but I haven't found anything quite like these symptoms and I've got a lot more to read. There are just too many possibilities. Is the anti-theft system the root of my problems, or is it just another symptom from everything being jostled so many times?

I'd get after the ignition barrel and go from there. Remove the plastic surround on the steering column and see if you can move/jostle the harness and get the same outcome. Try and figure out if it's internal to the barrel or further on down the line. If it's internal to the barrel, get a new one, swap her in and see where you're at with the rest of the problems.

[SpaceFrank]

I'm going to take off the steering column surround this weekend and go poking around. Does anyone know where to find any wiring diagrams or schematics for this part of the vehicle?

[STL_G8GT]

Gimme a bit I might have it on alldata