Q: 2009 Buick Lacrosse is setting DTC codes P2125 and P2138.

asked by on November 29, 2016

A 2009 Buick Lacrosse 3.8ltr with 112000 miles is setting a DTC P2125 and P2138 code. The vehicle went into reduced Engine Power Mode one time. It presently has good acceleration, with the exception of a slight surging when not in cruse contorl. I evaluated the Accelerator Pedal Position resistors by placeing a 5 volt source between pin A (ground) and pin C (5v) while monitoring the sensor line pin B with a Digitia Storage Oscilloscope. The displayed waveform is a smooth dc waveform with no intermittents. APP Sensor voltages are within parameters with an intriguing difference. The DSO indicates a square wave pattern with a duty cycle of84%, Positive Width of 15.8ms at 4.56 volts and 2.98ms at -.06 volts. with a repitition rate of 53.3 Hz. The square wave is indicated on APP 2 but not APP circuit 1. Also interesting is the fact the waveform presents itself when the Accererator Pedal Position is connected but dissapears when disconnected. APP sensor outputs go to the Throttle Body

My car has 122000 miles.

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Hi there. Try performing a snap throttle and see if the wave form changes on the Oscilloscope. If the waves do not change when performing a snap throttle, then the throttle position sensor on the pedal needs replaced. If the wave changes then the Throttle Position Sensor on the throttle body needs replaced. If you need further assistance with your engine having a loss of power with the codes P2125 and P2138 showing up, then seek out a professional, such as one from Your Mechanic, to help you.

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