Red. Engine Pwr/Serv. Stabilitrac- TB, Pedal, Cats, or Speed Sensors - Chevy Impala Forums
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post #1 of (permalink) Old 08-21-2018 Thread Starter
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I know this is beat like a dead horse, but hear me out. But this one is different I feel like. No codes for TB or Pedal. It's a 2012 impala v6. Basic version. 167k.

Bought the car doing this, thinking I could fix it easily. It has kicked my ass. Originally, a quick google told me it was the throttlebody. There was oil in the intake for some reason, so I cleaned it out and out a new MAF, EVAP sensor (had a code for it), and throttle body. Put it all in and was good to go. I got cheap, put the old throttle body back on curious if it was the MAF or the EVAP sensor, and it still ran fine with the old throttle body on. I returned the throttle body and got my money back.

The next day, driving to work, I noticed at WOT, or really anything past 1/4 throttle, the car would cut out/jolt it's way up in the RPMs and then BAM, service stabilitrac and reduced engine power. I shut the car off, restart it immediately, and the service stabilitrac and reduced engine power is off. As long as I'm easy on the gas they stay off and it drives fine. (Originally, they would never shutoff and it would stay in the limo mode). But, if I mash it to leave a red light anything past 1/4 throttle it does it again.

I've read about the Throttle body, speed sensors, and gas pedal. All of which seems to throw a code, either letting you know it's a TB or TPS problems, which wheel sensor, etc.

It has no codes for that.

Upon reading more about the car, I notice this model had a catalytic converter recall as well. From reading others posts with converters, it seems a few has had the same jolting/cutting out issue at WOT or whatever before the REP and stabilitrac lights kick in. I also have a code for P0420 which seems to be commonly the catalytic converter. My scan tool will read PIDs but I have no clue what I'm looking at there.

All the other codes from when I first got the car are back too.

PO192, P0420, C0242, and some misfire codes are popping up. There may be some I left out, but I feel the misfiring and such are just from the REP, because it runs and sounds smooth with the exception of the items mentioned above.

Nothing mentioned the TB, Speed sensor, etc.

Does the cats cause the REP and service stabilitrac issues as well? Did anyone else have these random codes when the culprit was the pedal or TB? What has me thrown off is how originally it would always be on. Also the jolting under heavy pedal was said to be cats in another post, but it sounds and smells fine, and at easy pedal no lights or any issues at all..
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post #2 of (permalink) Old 08-22-2018
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I own a 2014 Impala 2LTZ, and previously owned a 2008, 2011, and 2012 Impala LTZ - all purchased new.

I suspect your problem is in the left or right (or both) wiring harness for the front wheel speed sensors. The wiring is well known to develop breaks inside the insulation (in the wiring), causing the symptoms you are describing. The wiring fatigues from the up and down movement of the suspension, and the wheel’s turning. The insulated wiring is inside a black plastic wiring loom, which can be removed to examine the wiring. Look VERY CLOSELY for any damage or pinch-points, especially where the harness is clipped to the suspension. To reveal the damaged internal wiring, you may have to wiggle the outside of the wiring every few inches, while moving across the wiring. Several people (including me) have had the wiring damaged where it is held by a pinch clamp from the factory.

GM has issued left and right wiring service pigtails to replace the damaged wiring (instead of the entire fron harness). I do not have the part numbers, as they are specific to the vehicles based upon the VIN, and specific to the left and right sides.
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post #3 of (permalink) Old 08-22-2018
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Also read this (with good pictures): https://gm.oemdtc.com/7628/pi0631i-m...evrolet-impala
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post #4 of (permalink) Old 08-22-2018
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The OP's issue seems to happen even when he's going straight though - and he's getting warning lights that are not usually associated with the speed-sensor wiring issue (reduced engine power) - and it happens every time he goes above 1/4 throttle. Typically, the issues with the speed-sensor wiring occurs when making turns - and doesn't trip any of the reduced-power-related warning lights - and is also very intermittent.

However, I think the link in the post above may be onto something - that seems to be closer related to the symptoms that the OP is experiencing. I would definitely look into the engine-bay harnesses before the speed-sensor wiring.

Just my two cents. :-)
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post #5 of (permalink) Old 08-23-2018 Thread Starter
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JTROSKY nail on the head.

I replaced the throttle body today just for shits and giggles. Still doing the same thing. The back tires are bald, so I'm going to replace them tomorrow (although I highly doubt that has anything to do with it).

I guess next I'll get a gas pedal. If that doesn't do it I'll look into the speed sensor harness. I was really trying not to just blindly throw parts at it, but I guess that is where I'm at currently.

I did check the fuses mentioned in the link above, but they were all good. I did my best to inspect the wiring harness and I do not believe I've seen anything out of the ordinary. The larger one that lays across the top of them transmission seems to have some rub marks, possible issues on the bottom side where it touches, but after moving and taping it, still the same thing.

If anyone has any other suggestions or help, please chime in. If not, I'll keep updating as I replace parts in hopes that it will help someone else who is searching in the future.
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