What Does P0120 Mean?
The ECM has detected a general malfunction in the throttle position sensor (TPS) or accelerator pedal position sensor (APP) circuit designated as sensor A. This could be an open circuit, short circuit, or signal outside the expected voltage range. On electronic throttle control (ETC) systems, this code may trigger reduced power mode as a safety precaution since the ECM cannot accurately determine throttle or pedal position.
Common Causes
35%
Failed throttle position sensor with worn internal resistive element or broken wiper contact
25%
Damaged or corroded TPS/APP sensor connector causing intermittent signal loss or voltage offset
25%
Failed accelerator pedal position sensor module (on ETC systems) with internal circuit failure
15%
Wiring harness damage between TPS/APP sensor and ECM causing open or short circuit
Diagnostic Steps
1
Monitor TPS A and APP sensor A voltages on a scan tool while slowly sweeping the throttle from closed to wide open. The voltage should transition smoothly from approximately 0.5V to 4.5V with no dropouts or dead spots.
2
Inspect the TPS connector at the throttle body for corrosion, moisture, or damaged terminals. On ETC systems, also inspect the APP sensor connector at the accelerator pedal.
3
With the sensor disconnected, verify 5V reference voltage and ground at the TPS connector. If 5V reference is missing, check for a short to ground on the 5V reference circuit shared with other sensors.
4
Measure TPS sensor resistance between signal and ground terminals while slowly rotating the throttle shaft. Resistance should change smoothly with no sudden jumps indicating worn spots on the resistive element.
5
On ETC systems, check for TSBs or recalls related to throttle body or APP sensor failures, as many manufacturers have known issues with specific model years.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The ECM has detected a general malfunction in the throttle position sensor (TPS) or accelerator pedal position sensor (APP) circuit designated as sensor A. This could be an open circuit, short circuit, or signal outside the expected voltage range. On electronic throttle control (ETC) systems, this c...
The most common cause of P0120 (Throttle Pedal Position Sensor/Switch A Circuit Malfunction) is: Failed throttle position sensor with worn internal resistive element or broken wiper contact
Typical repair costs for P0120 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A TPS/APP malfunction can trigger reduced power mode or limp home mode, severely limiting vehicle speed and acceleration. In rare failure modes, unintended throttle opening or closing could occur, posing a significant safety risk in traffic.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0120 to identify the root cause.
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Quick Info
Category
Powertrain
System
Electronic Throttle Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
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