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Could be a bad APP sensor or even a bad ECM…below is what sets that DTC and the Circuit/System Verification…if you lack electrical diagnostic skills I’d seek out an auto electrical specialist.
You need an oscilloscope to get a trace pattern of the pedal. It’s either the pedal itself or the circuit. Basically one goes 0-5v the other goes 5-0 volts. At each pedal position up and down the ecm is looking for the correct voltage from each circuit. Without the scope best thing you can do is DMM the resting voltage on each circuit and the WOT on each circuit. Most shops would just throw a new APP on and call it good. You don’t by chance have a pedal commander so you?
Best guess, is the swiper sensors in the accelerator pedal. P2138 Accelerator Pedal Position (APP) Sensor 1-2 Correlation ECM
[img]https://m.media-amazon.com/images/I/51eBEvwOtdL._AC_SL1500_.jpg[/img]
the hail mary pass if mileage is under 50K, is to pull the pedal, pick up a can of spray electrical cleaner,
[img]https://m.media-amazon.com/images/I/61OrSbvCKCL._AC_SL1500_.jpg[/img]
The spray the cleaner in any opening you can find to Douche the inside of the sensor and move the pedal up and own, so the pair of swiper arms can clean themselves and the stat pads they swipe against to solve the problem. Also clean the connector and sensor pins, before you put it all back in.
If higher mileage, the hail mary of trying to clean the sensor swipers to stat pads with sensor still in the assembly may still work, or it may be the sensor arm and stat pads are just too worn or corrode out. At this, comes down if you have the talent to pull sensor from the assembly/pull it apart to clean it better and tweak arms ( and not loose a eye since GM does not sell just the sensor, but the entire assembly with sensor only),
Or just time to spend the C note for a new pedal assembly. Gm 19417903, 25835421, 15864594, and 12569599
And would go with either gm or standard motor products, https://www.rockauto.com/en/parts/ac...on+sensor,5061
And just a quick note to way back step, before you pull the assembly out, pull the connector to give it a quick clean and plug it back in, since someone before you may have has a throttle controller on the car, and did not plug the connector all the way back in when they removed it before selling the car.
If you have a throttle controller on the car, then disconnect it to see if problem is solved, with the problem in the after market controller instead.
