What causes a P2123 code?

P2123 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a P2123 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P2123 active.

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

OBD-II

P2123

P2123 Accelerator Pedal Position Sensor 1 High Circuit

What it means

The Engine Control Module (ECM) detects the voltage from the Accelerator Pedal Position (APP) sensor 1 is higher than the expected operating range, typically exceeding 4.8 volts.