Throttle Position Sensor/Switch A Circuit Low Input
P0122 indicates the throttle position sensor (TPS) is sending a voltage signal that is lower than the engine control module expects. This prevents the engine from accurately measuring throttle input, affecting fuel injection timing and air intake control.
What You Might Notice
- Rough or low idle
- Very high idle speed
- Engine stalling
- Surging or hesitation during acceleration
- Little to no acceleration response
Most Common Causes
- 1
Faulty Throttle Position Sensor
The TPS itself has failed internally and is producing out-of-range low voltage signals. This is the most common cause and requires sensor replacement.
- 2
TPS Circuit Short to Ground
A damaged wire or connector in the TPS circuit is shorted to ground, pulling the voltage signal abnormally low. This typically requires wiring harness inspection and repair.
- 3
TPS Not Mounted Securely
Loose mounting can cause intermittent electrical contact or mechanical misalignment, resulting in unstable voltage readings from the sensor.
- 4
Damaged Engine Control Module (PCM)
Though rare, a faulty PCM or its TPS input circuitry can misread normal sensor voltage as too low. This is typically a last-resort diagnosis after sensor and wiring are ruled out.
How to Diagnose It
- 1
Check Faulty Throttle Position Sensor — The TPS itself has failed internally and is producing out-of-range low voltage signals. This is the most common cause and requires sensor replacement.
- 2
Check TPS Circuit Short to Ground — A damaged wire or connector in the TPS circuit is shorted to ground, pulling the voltage signal abnormally low. This typically requires wiring harness inspection and repair.
- 3
Check TPS Not Mounted Securely — Loose mounting can cause intermittent electrical contact or mechanical misalignment, resulting in unstable voltage readings from the sensor.
- 4
Check Damaged Engine Control Module (PCM) — Though rare, a faulty PCM or its TPS input circuitry can misread normal sensor voltage as too low. This is typically a last-resort diagnosis after sensor and wiring are ruled out.
How to Fix It
- 1
Replace Throttle Position Sensor
Remove the faulty TPS from the throttle body and install a new or refurbished sensor. Ensure proper mounting torque and electrical connector seating, then clear the code with a scan tool.
- 2
Inspect and Repair TPS Wiring Harness
Check the TPS connector and wiring for corrosion, loose pins, or damage. Repair or replace any compromised sections of the harness, and verify continuity with a multimeter.
- 3
Reseat TPS Mounting and Connectors
Remove the sensor, clean the mounting surface and connector contacts, then reinstall the TPS with proper torque specification. Ensure the connector clicks firmly into place.
- 4
Test and Replace Engine Control Module
If sensor, wiring, and connections are confirmed good, use an advanced diagnostic scanner to validate PCM functionality. Replace the PCM only if it is confirmed faulty.
Need a deeper diagnosis?
Search for related repair guides or browse by system.