What causes a P2121 code?

P2121 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 P2121 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P2121 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

P2121

P2121 Throttle/Pedal Position Sensor 'A' Range/Performance

What it means

The Engine Control Module detects that the Accelerator Pedal Position (APP) Sensor 1 signal is out of its specified range or is inconsistent with the secondary pedal sensor signal.