P1221 — Accelerator potentiometer track 1 fault | Drive-by-wire potentiometer 1 signal implausible

Diagnostic algorithm

1. Retrieve and record stored codes and live data for both pedal sensor channels. Note conditions when code set.
2. Clear codes and attempt to re-create fault by cycling ignition and operating pedal while watching live data.
3. Visually inspect pedal assembly, connector and wiring route for damage, pin corrosion or water. Repair as needed.
4. With key ON (engine OFF) backprobe the sensor: verify 5 V reference, sensor output voltages for track 1 and track 2, and a good ground. Compare to expected ranges.
5. Move pedal through full travel while monitoring voltages: outputs should change smoothly without sudden jumps. Wiggle the harness/connector to check for intermittent faults.
6. If reference/ground are missing or incorrect, trace and repair wiring to ECU or body ground; retest.
7. If wiring and supply are good but track 1 signal is out of range or erratic while track 2 is normal, replace the accelerator pedal sensor/assembly.
8. If both tracks are inconsistent but wiring is intact, consider ECU connector/ECU fault — only after verifying harness and sensor replacements fail to correct problem.
9. After repairs, clear codes and perform a road test and scan to confirm fault does not return and throttle response is normal. Perform any required pedal/throttle adaptations per manufacturer procedure.