Throttle / Pedal Position Sensor 'A' Circuit Low Input

Drive-by-wire systems have two TPS sensors built into the throttle body and two more on the pedal — for redundancy. The PCM checks they agree. P0122 means TPS-A's signal voltage went below the floor (typically <0.2 V), which is electrically impossible at any throttle position. It's either an open signal wire, an open 5V reference, or a failed sensor. The PCM will go into limp mode (reduced power) the moment this sets.

TPS-A signal voltage below minimum threshold (typically <0.2 V) for more than a brief moment.

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 1Key on, engine off. Measure 5V reference at throttle body connector — should be ~5.0 V.
2. 2If 5V is missing, check for shorts on other sensors sharing that reference (unplug one at a time).
3. 3Measure TPS signal voltage at the connector while sweeping the throttle by hand (if accessible).
4. 4Scope both TPS-A and TPS-B together — they should track in opposite directions or mirror at a fixed offset depending on system.

• Open signal or 5V reference wire to throttle body
• Failed throttle body / TPS
• Corroded connector at throttle body
• PCM 5V reference shorted

$200 (throttle body) to $500 (wiring repair + relearn).