The throttle position sensor (TPS) tells the engine computer how far the throttle is open. The computer uses it for fueling, ignition timing, idle control and, on many automatic transmissions, shift timing and line pressure. On vehicles with electronic throttle control, the throttle body has two position sensors and the accelerator pedal has its own pedal position sensors; any disagreement between them triggers reduced-power mode.
Bad throttle position sensor symptoms
- Hesitation, stumbling or surging when accelerating; see car jerks when accelerating
- Erratic or high idle, or stalling
- Reduced engine power mode with a warning light, and the throttle barely responding
- Harsh, early or late shifts on automatics that use throttle position for shift timing
- Check engine light with throttle or pedal codes
Throttle and pedal position codes
| Code | Meaning |
|---|---|
| P0121 | Throttle position sensor A range/performance |
| P0122 / P0123 | Sensor A circuit low / high |
| P2135 | Throttle sensors A and B disagree |
| P2138 | Pedal sensors D and E disagree |
| P2122 | Pedal sensor D circuit low |
| P2101 | Throttle actuator motor range/performance |
Cable throttle vs drive-by-wire
With a throttle cable, the TPS is a separate three-wire sensor bolted to the side of the throttle body, and it can usually be replaced on its own. With electronic throttle control, the position sensors are built into the throttle body, and the pedal sensors are built into the pedal assembly, so the fix for a confirmed sensor fault is usually a new throttle body or pedal.
What does reduced engine power mean?
Reduced engine power (or a wrench, throttle or similar warning light) means the computer has limited throttle opening because it cannot trust the throttle or pedal signals, or the throttle motor is not responding. It is a safety mode, not a sign the engine is damaged. Throttle body carbon, a corroded connector and low system voltage are common causes; see limp mode.
How to test a throttle position sensor
- Graph the throttle position reading on a scan tool while slowly opening and closing the throttle, looking for dropouts or spikes.
- On drive-by-wire systems, compare both throttle sensors and both pedal sensors; their readings should track each other smoothly.
- Check the 5-volt reference and ground at the connector.
- Clean the throttle body and inspect the connector for corrosion before replacing parts.
Most electronic throttle systems need a throttle or idle relearn after cleaning or replacement. If the engine still runs poorly with good throttle readings, check for a vacuum leak and a dirty MAF sensor, and see rough idle.
Trouble codes: P0120 Throttle Position Sensor A Circuit · P0124 Throttle Position Sensor Intermittent · P0220 Throttle Position Sensor B Circuit · P0221 Throttle Position Sensor B Range · P0222 Throttle Position Sensor B Low · P0223 Throttle Position Sensor B High · P2127 Pedal Position Sensor E Low · P2128 Pedal Position Sensor E High · all OBD2 codes.
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