2012 Sonic P2138 problems.

[Dafson2]

Hi all, I have a 2012 Sonic LT 1.8 Manual with around 80k miles. About a month ago it randomly popped up with CEL, traction control, and lower power mode code 84. Tried multiple restarts and they stayed on, drove to shop, it was throwing codes P2127, P2128, P2138. Mechanic said it was the sensor in the accelerator pedal and the whole assembly needed to be replaced.

I bought a new assembly on eBay for $20. It looked OEM and fit perfectly. After the swap I disconnected negative from battery and after a few drive cycles all the lights went off. About one week later they all came back after idling for an extended period. Only CEL remained after restart and they did not come back.

Then about 2 weeks later all the lights came back on, now sometimes they will turn off after restart but normally they are always on. If they are off they usually come back soon as I touch gas pedal. Had code reread and this time it’s only P2138. Mechanic said throttle body, so another 80 on eBay and I changed that. All lights remain on after disconnecting battery multiple times they still won’t go away.

I reseated all electrical connections I could find, but not sure where other end of cable from accelerator pedal is, unless it’s directly to throttle body.

Any other ideas? Usually the lights are off (other than CEL) in the morning and come back on after driving for a minute.

 

[gnonne]

Just Guessing

Maybe the $20 part was bad. It worked for a week, then back to the same issue. Since you re-checked the connections, that does not leave much else but a bad part.

Also, how cold is it and do you leave the car outside? Connections could be problematic in sub-zero weather even if parts are good - computer can't tell the difference.

Just Guessing

 

[Dafson2]

Maybe the $20 part was bad. It worked for a week, then back to the same issue. Since you re-checked the connections, that does not leave much else but a bad part.

Also, how cold is it and do you leave the car outside? Connections could be problematic in sub-zero weather even if parts are good - computer can't tell the difference.

Just Guessing

I also thought maybe the part so I have a new (OEM) one on order. I live in Rhode Island so It has been cold, but the most recent time all the lights came back it was actually one of the warmer 40 or 50° days. I think I checked all the connections but I don’t know where the pedal connects to.

 

[Dafson2]

So today I hadn’t touched car, last night code 84 soon as I turned it on. Went to grocery store, about 4-5 miles no code 84 or other lights. Left grocery store and they came back on after I backed out of the space.

This is so frustrating.

 

[Dafson2]

Update

Got another new pedal/APP sensor for the sonic. Did not disconnect battery and lights went off. CEL even went off by itself after a couple drive cycles. Started it up to move parking spots and all lights came back. Ugh!!

 

[JTee2017]

Got another new pedal/APP sensor for the sonic. Did not disconnect battery and lights went off. CEL even went off by itself after a couple drive cycles. Started it up to move parking spots and all lights came back. Ugh!!

Just out of curiosity, how old is the battery? Even if it isn't too old, cold weather will put stress on the battery especially if trips are short and many starts. Also, check the battery terminals and clean them well and apply some light grease to them. Check any possible ground connection points also.

A weak battery or cell that intermittent shorts will cause a lot of weird conditions. You could try a battery load test. . at least 100 amps for 10 to 15 second with a good load tester.

 

[Dafson2]

Just out of curiosity, how old is the battery? Even if it isn't too old, cold weather will put stress on the battery especially if trips are short and many starts. Also, check the battery terminals and clean them well and apply some light grease to them. Check any possible ground connection points also.

A weak battery or cell that intermittent shorts will cause a lot of weird conditions. You could try a battery load test. . at least 100 amps for 10 to 15 second with a good load tester.

Purchased new battery October 2017. Had to clean the terminals pretty good to get old battery off, but will do again.

 

[Dafson2]

So weird!

Drove car about 30 miles this morning. No lights. Went into store came out and lights came on right at start up. What could be happening? Something must be happening when car heats up.

 

[gnonne]

Theory...

The TSB you referenced in the other thread showed dealer part numbers for various sealants. I guess leaks can occur at different spots on different models, which are all covered by the TSB.

If you have a water intrusion problem where the connectors are located (behind kick panel on Sonic) it makes sense that the lights would come on after it warms up - the ice has melted and shorts out the connectors.

I'd get inside that kick panel and see what is going on. Dry everything off, wrap the connectors in a dry shop towel and see how it works. If the towel gets wet again, find the leak.

It might just be a serious case of condensation inside the body and not a leak. I've had issues with significant frost inside my windows recently due to high humidity in the car and very low temps outside (when it stays in the driveway.)

 

[Dafson2]

The TSB you referenced in the other thread showed dealer part numbers for various sealants. I guess leaks can occur at different spots on different models, which are all covered by the TSB.

If you have a water intrusion problem where the connectors are located (behind kick panel on Sonic) it makes sense that the lights would come on after it warms up - the ice has melted and shorts out the connectors.

I'd get inside that kick panel and see what is going on. Dry everything off, wrap the connectors in a dry shop towel and see how it works. If the towel gets wet again, find the leak.

It might just be a serious case of condensation inside the body and not a leak. I've had issues with significant frost inside my windows recently due to high humidity in the car and very low temps outside (when it stays in the driveway.)

Yea I took both kick panels off and didnt see any signs of water. It certainly does get humid in car this of year though. Still looking to find a wiring diagram for the APP/Throttle sensor

 

[JTee2017]

Well .. . I guess it isn't worth checking the battery and connections. . .

 

[Dafson2]

I give up

Well this car has defeated me. I thought for sure that water was leaking on something causing this issue. I thought maybe after ice/snow melted it would leak and that’s why it only happened after I drive for awhile. But today was nice and sunny. No snow no ice. Car drove fine for 25 minutes then lights kicked on.

I’ve checked every electrical connection I can find. I’ve cleaned battery cables and grounds.

I give up. Gonna save some money so I can afford to take it to Chevy to figure out.

 

[Mike DZ]

Are you just getting the P2138 code with the CEL now? I had a recurring P2138 in an AVEO and changed out the throttle body to find out later that the electronic plug that connected to the throttle body was not making a good connection. Solution was a one cent zip tie.

 

[Dafson2]

I’ll take a look.

Are you just getting the P2138 code with the CEL now? I had a recurring P2138 in an AVEO and changed out the throttle body to find out later that the electronic plug that connected to the throttle body was not making a good connection. Solution was a one cent zip tie.

Yea CEL and low power mode and only code 2138. I will certainly take another look at the throttle body connection. Was it visibly loose? I also replaced my throttle body and it certainly seems ok.

 

[Mike DZ]

No, not visibly loose. I ended up zip tieing so that the connection was "tighter", but there was no obvious movement. of the connector. My theory was that engine and road vibration caused a momentary disconnect of one of the pins. I was ready to rewiring the car side connector until I got the zip tie snugged up correctly.

 

[Dafson2]

No, not visibly loose. I ended up zip tieing so that the connection was "tighter", but there was no obvious movement. of the connector. My theory was that engine and road vibration caused a momentary disconnect of one of the pins. I was ready to rewiring the car side connector until I got the zip tie snugged up correctly.

Well I added the zip tie and blew some compressed air in the connection. (I’m getting tired of taking off that stupid air intake house) Tomorrow will tell I suppose.

 

[Dafson2]

Still being stupid

Well even with zip tied electrical connector at throttle body all the lights came on after 30 min on my way to work. It is a very snowy day here today, but I’m out of ideas, appointment scheduled at Chevy tomorrow. Unless anybody else has any ideas.

 

[Dafson2]

Bad ECM

Well Chevy says ECM is bad. Only 390 plus diagnostic fee so not too bad. I see part ACDelco 12679199 online and looks easy to physically replace. Is it something I can program?

 

[ScarabEpic22]

Well Chevy says ECM is bad. Only 390 plus diagnostic fee so not too bad. I see part ACDelco 12679199 online and looks easy to physically replace. Is it something I can program?

You need a Tech II/MDI/Mongoose Pro cable and a subscription to GM SPS to program a new ECM. So you could, but the cost to entry is about $3-400 for the Mongoose cable and a 2-day SPS subscription is $55+tax. The dealer will probably charge 1hr of labor at $100-125.

If you could find a local shop with a SPS subscription, they'd be able to do it for you as well, but still for .5-1hr of labor.

Where are you located? I have a Mongoose cable, but I'm in Seattle, WA so it probably won't be convenient to meet up.

 

[Dafson2]

You need a Tech II/MDI/Mongoose Pro cable and a subscription to GM SPS to program a new ECM. So you could, but the cost to entry is about $3-400 for the Mongoose cable and a 2-day SPS subscription is $55+tax. The dealer will probably charge 1hr of labor at $100-125.

If you could find a local shop with a SPS subscription, they'd be able to do it for you as well, but still for .5-1hr of labor.

Where are you located? I have a Mongoose cable, but I'm in Seattle, WA so it probably won't be convenient to meet up.

Thanks for the offer, but yea I live in Rhode Island so it’s a bit too far. The dealer cost isn’t too bad so I’m just going that route. It’s just annoying to pay 260 for a part that’s 100 anywhere else. And even worse i’m a dang IT specialist so computers are my thing.

Will let post die unless issue reoccurs after ECM change. Thanks for the help everybody!