P2121: Throttle/Pedal Position Sensor/Switch D Circuit Range/Performance

What does P2121 mean?

P2121 means pedal signal D is electrically intact but implausible. Ford's 2012 OBD summary sets it only on second-generation ETC systems, whose pedals carry three tracks D, E and F: if sensor D disagrees with the others by more than 1.1 degrees, the PCM stores P2121 without MIL but with the wrench lamp, and pedal response becomes rate-limited using the healthy tracks. Mitsubishi lists P2121 for the accelerator pedal sensor on the 2022 Outlander as a one-trip code that turns the MIL on. Newer Ford and GM systems with two tracks report such disagreement as P2138 instead. Circuit faults on D are P2120 and P2122-P2124; P2126 is the same check for track E. The car stays drivable but reacts softly to the pedal.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Wrench or engine warning lamp on
• Softened, delayed acceleration
• Idle may rise when the brake is not pressed

Common causes

• High Worn or dirty track D giving an offset reading
• Medium Contact resistance at the pedal connector
• Low Shared reference or ground line shifting one signal

Likelihood is a general estimate across vehicles; your make and model may differ.