P2138Powertrain
Powertrain · SAE
Accelerator Pedal Position Sensors D/E — Implausible Correlation
Meaning
The ECU continuously compares the signals from the two redundant channels of the accelerator pedal position sensor (APP D and APP E). This code is set when the difference between the two signals exceeds the permitted correlation threshold, or when the signals do not vary proportionally during pedal travel.
Common causes
- APP sensor with partially failed track D or E, or anomalous resistance on one track
- Wiring with parasitic resistance or partial short circuit on one of the two circuits
- Corroded or intermittent pedal connector on one of the channels
- Faulty 5 V reference supply feeding only one channel abnormally
- Mechanically worn APP sensor with non-linear track behaviour on one wiper path
Symptoms
- Check-engine light (MIL) on
- Limp-home mode with power limitation
- Irregular or jerky pedal response
- Often associated codes P2122 and P2127
- Unable to accelerate normally
Severity
High: a mismatch between APP D and E signals indicates the redundant safety system is compromised; the ECU limits power to protect the vehicle.
What to do
- Compare APP D and APP E live values with a scan tool over the full pedal travel: they must vary proportionally without deviations exceeding the specification threshold
- Measure the resistance of both APP sensor tracks at various pedal positions
- Verify the 5 V supply and ground for both channels separately
- Inspect the pedal sensor connector for corrosion, bent pins, or intermittent contacts
- Replace the APP sensor if the tracks are not correlated or one is out of specification