Trans slipping, auto stop not working, engine RPM racing, gauges funky...

[bbOOmm]

Today my 2008 Tahoe Hybrid went funky. No codes, no engine light, just suddenly it seemed that the transmission started slipping. The engine RPM would suddenly go up when accelerating. Then at a stoplight, my engine RPM went to over 3000 without touching the gas pedal. I tapped the gas pedal thinking something was stuck, no response from the pedal. I turned off the ignition and restarted... it then idled fine, but once I started moving again, the slipping was still there.

Stopping at more stoplights, the engine auto-stop was not working. The only way I could get moving was babying it, the instant I heard the -slip- I let up on the accelerator, it would shift to the next gear and I'd try again. Once I would get to 4th, it was pretty solid. However I was noticing my economy gauge and tach needles were moving around without any pedal input, terrain changes or even different engine sounds.

I stopped to get a soda, turned off the engine for 10 minutes, it started back up just fine, the auto stop worked before I started moving. When I started driving again, the slip was there... top end of first would slip, second and third were really weak, 4th was pretty solid. After this restart, now when coming to stops, the engine auto-stop would try to stop the engine, the instant it would shut down, with a clunk, it would restart. I had to stop that by shifting into manual mode every time I'd approach a stop, that clunk was un-nerving.

Randomly there would be a single light jerk in 4th at highway speeds. Not often. It feels like as if I would left off the accelerator slightly, then accelerate again. This would be in cruise, my foot nowhere near the gas pedal.

Being an electronics nerd, seeing random craziness in logic systems that would get corrupted somehow... brownout, EMP, ESD, firmware corruption etc ... all these problems seem to be "electronic" in nature... that's what it seems like since everything controlled by some sort of ECM, TCM, Hybrid Controller, battery controller etc etc. So what I'm thinking is starting with the most basic fix that sometimes works with other technology.....unplugging the batteries.... both the 12V and the 300V and letting it sit for a while... then reconnect the batteries. A good ol hard reset.

First off, I have no clue if this touch screen nav/radio needs a code like the older TheftLock ( how do I figure out the code? I looked online, I'm not finding anything for the touch screen radios)

Secondly, anything else that will need to be re-learned. I read something about the one touch window opening/closing feature would be forgotten. Is that true? Whats the re-learn procedure?

Anything else I should be looking for? Anyone have these problems before? What was the fix?

Thanks

Dave in Kewaskum, WI
2008 Chevy Tahoe Hybrid
102K miles
Transmission flush and fluid change 500 miles ago

 

[bbOOmm]

Update:

I pulled the Hybrid disconnect and disconnected the 12v battery, left it disconnected for an hour. No change. In fact I don't think the hybrid battery was fully disconnected because the radio still had the current time, radio presets, the trip counters and other info were not reset to zero... the 12v battery was disconnected, the hybrid battery's disconnect is a pretty whimpy "jumper", no way that fully disconnects the whole battery pack... it might prevent a contactor(relay) from actuating, but there is no way that little jumper cuts off the output of the pack.

So for my next trick up my sleeve, I'll pull the fuses for the ECM, BCM, TCM... what ever control module fuses I can find, I'll pull the fuses.

An update on symptoms. I'm able to replicate the ability to reset the engine auto-stop by turning off the engine and restarting. Sitting in park or drive without moving, auto-stop works, But once I start moving, the auto-stop stops working.

I was able to get the auto-stop to work again without a restart. I was trying to take off in second gear to see if it slips directly taking off in M2. I have to test that some more to get repeatable results, but I found that after doing that M2 takeoff and shifting back into drive, the auto-stop worked again. It worked only till the engine started again by the need for ICE torque, then the auto-stop quit working again. One time doing this, when I came to a full stop in D after the auto-stop quit working again, I let up on the brake, the engine RPM jumped to close to 3K. I pressed on the brake again, the engine RPM when to idle. I let up on the brake, the engine RPM increased again. BUT the vehicle did not move forward in a speed in relation to the engine RPM, it almost felt dogged down, between gears or 2 gears at once or not enough pressure to engage the clutches???. I had to kill the engine then restart to clear that condition.

I noticed some sounds and lack of sounds too. I noticed the whine of the regenerative braking sometimes is not present like normal. In some instances where the road is smooth and quiet, at highway speeds, it sounds like the motors are whining. I never noticed this before. I also noticed some noise at idle in D... I have to investigate this. sometimes it sounded like a pump cavitating on air then catching and pressurizing, then cavitating -repeat, other times it was more of a quiet clunk/click that corresponded with a 100 or so engine RPM jump for a brief second, then a lull for a second, then that clunk -repeat.

I'll eff around with this some more when the rain stops.

 

[bbOOmm]

Update #2

The rain stopped ... yay. So I pulled the fuses for the ECM(batt), TCM(batt), and HVAC(batt), I turned the key to start, it was a no crank-no start condition and set codes. The trans aux pump was heard clearly ... kind of noisy in my opinion. I then put those fuses back in and then pulled the fuses for FMCM and something else that slips my mind, turned the key to ignition, I didn't try to crank. I removed the key again, reinstalled those fuses and on the instrument panel fuse block, I pulled the BCM fuse. I started the engine - supprised it started... ran it for about a minute then shut down. I reinstalled the BCM fuse.

I then started the engine, hooked up the scan tool, read the codes, there was 9 codes. I cleared them and went for a drive. It was choppy and clunky at first, the engine auto-stop was not working again. So after 10 minutes of driving at highway speed, and a few stops, I parked and shut down for a few minutes. I then restarted, it idled fine, then auto-stop activated while I was still parked. I then drove it some more, I did not notice any slip this time. I made a few more turns, this time auto-stop was working. I accelerated moderately from several stops, I did not notice any slipping. My shift points were a little higher than what it was before and since I purchased it. Which is good... I did not like those shift points, seemed too low and mushy.

Going through the village I live in, 25mph, I was scooting on battery only just fine.

So, it appears that somehow, some programming got effed up in some controller and effed up the whole works.

If this happens again, I'll pop fuses one by one and check drivability till I find the controller that resets the condition. I'll then post my findings for an exact fuse to pull to reset/clear the issue. I'll probably pull that controller and inspect the circuit board for any corrosion, moisture intrusion, cold solder joints etc.

Till then, if anyone has these issues... pull the all controller fuses to erase the error, where ever it is, and put them all into learn mode for the first engine cycle.

 

[dnt1010]

102k miles Wow that is great for a 10 year old vehicle. On your issues I have read on other forums that what you have described matches the symptoms of a bad 12V battery? If it has a AC Delco battery in it now the date code is on the top and probably starts with a P? the first two numbers are the month and third number indicates the year of manufacture The last digit (a letter) indicates the plant of manufacture. Here is a pic of mine in an 09 Tahoe Hybrid (198k miles) with the AC Delco 770 CCA supposedly a very good battery for these units?
The number on mine is P024R so it looks like mine was manufactured February of 2014 and is quickly approcaching the 5 year mark, which makes it pretty long in the tooth for a 12V auto battery nowadays. I just had my local auto parts store test it and it tests GOOD but it is still suspect if I start having oddball problems such as you are having. Please post back if you have resolved your issue and what the actual cause was. That info could be invaluable to the Hybrid owners out there that are risking their hard earned dollars on an obsolete technology that is bound to fail! Hahahaha

 

[Rickz04Yuk]

Any update?

 

[Doubeleive]

if the hybrid has a maf sensor (i'm assuming it does) try replacing that, could possibly be the source of all your issue's

 

[dnt1010]

It is easy to overthink these issues, from what I read it was most likely the 12V battery. I hope that he installed a new battery and is good to go. On the Hybrids the hybrid battery actually cranks the engine over so people are waiting for a slow crank to happen and it confuses them that the 12V under the hood could be bad and the engine still cranks like crazy at around 700 rpm LOL. Electronics do NOT like low volatge. and the 12V under the hood supplies power to all the electronic controls. Could of course be a bad battery ground cable too that is a known issue and should be checked.

 

[swathdiver]

Update #2

The rain stopped ... yay. So I pulled the fuses for the ECM(batt), TCM(batt), and HVAC(batt), I turned the key to start, it was a no crank-no start condition and set codes. The trans aux pump was heard clearly ... kind of noisy in my opinion. I then put those fuses back in and then pulled the fuses for FMCM and something else that slips my mind, turned the key to ignition, I didn't try to crank. I removed the key again, reinstalled those fuses and on the instrument panel fuse block, I pulled the BCM fuse. I started the engine - supprised it started... ran it for about a minute then shut down. I reinstalled the BCM fuse.

I then started the engine, hooked up the scan tool, read the codes, there was 9 codes. I cleared them and went for a drive. It was choppy and clunky at first, the engine auto-stop was not working again. So after 10 minutes of driving at highway speed, and a few stops, I parked and shut down for a few minutes. I then restarted, it idled fine, then auto-stop activated while I was still parked. I then drove it some more, I did not notice any slip this time. I made a few more turns, this time auto-stop was working. I accelerated moderately from several stops, I did not notice any slipping. My shift points were a little higher than what it was before and since I purchased it. Which is good... I did not like those shift points, seemed too low and mushy.

Going through the village I live in, 25mph, I was scooting on battery only just fine.

So, it appears that somehow, some programming got effed up in some controller and effed up the whole works.

If this happens again, I'll pop fuses one by one and check drivability till I find the controller that resets the condition. I'll then post my findings for an exact fuse to pull to reset/clear the issue. I'll probably pull that controller and inspect the circuit board for any corrosion, moisture intrusion, cold solder joints etc.

Till then, if anyone has these issues... pull the all controller fuses to erase the error, where ever it is, and put them all into learn mode for the first engine cycle.

How's it going with the truck Dave?

 

[Mrsbleam]

I have a 2008 Tahoe Hybrid with 126K miles and it does everything Dave described above. First thing we did was replace the 12V battery and it did not fix the issues. I've read elsewhere that replacing the hybrid batteries resolves the issue, but I'd like some confirmation before throwing that kind of money at the issue.

 

[BG1988]

it's the AUX pump AUX pump controller or HV battery.... my engine races to 2,000rpm if the A/C is on this is directly connected to the HV battery... not enough to trip a code. for the HV battery... 106k miles original battery....


I would also check and see if the Baro matches the MAP sensor Key ON


this will also cause the engine race it used to go to 3000-6,000 rpm randomly... Engine RUNAWAY while in gear but did not "move"


6,000 rpm was full throttle... Self destruct mode