P0120
Throttle/Pedal Position Sensor/Switch A Circuit Malfunction
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The P0120 code indicates a general malfunction in the Throttle Position Sensor (TPS) circuit. The TPS tells your engine's computer exactly how far open the throttle plate is — this is essential for determining how much fuel to inject and when to shift the transmission. When the ECM detects a signal outside the expected range or an illogical reading from this circuit, it sets P0120.
The most common cause is a worn-out TPS. These sensors contain a resistive track that a wiper slides across as you press the gas pedal. Over tens of thousands of miles, this track wears down and develops dead spots. Wiring damage from engine heat is another frequent cause. When this code triggers, most vehicles enter a reduced-power "limp mode" that limits your speed to protect the engine and transmission.
This repair is usually straightforward and affordable. A standalone TPS sensor typically costs $20–$80, and replacement involves removing two or three screws and unplugging a connector. On vehicles with electronic throttle bodies, the sensor may be integrated into the throttle body assembly, which costs more. Before replacing parts, clean the connector with electrical contact cleaner and inspect the wiring. If the code returns after sensor replacement, the throttle body itself may need attention.
Severity
Symptoms
- •Check Engine Light illuminated
- •Engine hesitates or stumbles during acceleration
- •Vehicle may enter limp mode with limited speed
- •Unstable or surging idle
- •Intermittent stalling, especially at low speeds
Likely Causes
The TPS uses a resistive element that wears over time. Dead spots or worn tracks cause the sensor to send erratic or incorrect voltage signals as the throttle opens and closes.
Heat from the engine and vibration can damage the wires running to the TPS, creating intermittent opens or shorts that disrupt the voltage signal.
A poor connection at the TPS plug introduces resistance or intermittent contact, causing the ECM to receive inconsistent throttle position data.
On electronic throttle bodies, carbon buildup or internal motor/sensor failures can prevent the throttle plate from matching the commanded position, triggering a circuit malfunction code.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the Throttle Position Sensor (TPS)
- Repair or replace damaged TPS wiring
- Clean the throttle body and TPS connector
- Replace the throttle body assembly if electronic throttle body has internal failure
Shop Parts
Videos
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