P0120 OBD2 Code Guide
P0120 is a sensors diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
Throttle/Pedal Position Sensor/Switch A Circuit Malfunction
Code P0120 signifies an electrical fault within the 'A' circuit of the Throttle Position Sensor (TPS) or Pedal Position Sensor (PPS). The Powertrain Control Module (PCM) uses this sensor to precisely monitor the throttle blade's angle, which directly correlates to the driver's acceleration input. A malfunction in this circuit means the PCM is receiving an implausible signal, an intermittent signal, or no signal at all from sensor 'A', leading to incorrect fuel delivery and transmission shift strategies, and potentially affecting engine performance and drivability.
Code verification standard
P0120 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 P0120 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
P0120 diagnostic path
- 1Begin by thoroughly inspecting the throttle body area, TPS/PPS sensor, and its electrical connector and wiring harness for any obvious damage, corrosion, loose connections, or frayed wires. Pay close attention to areas where the harness might rub against engine components.
- 2Connect an OBD-II scan tool and monitor the live data stream for the TPS/PPS 'A' sensor. Observe the voltage readings at idle and as the throttle pedal is slowly depressed and released. Look for smooth, consistent voltage changes without any drops, spikes, or flat spots. Compare the readings to manufacturer specifications (typically 0.5V at closed throttle and 4.5V at wide-open throttle).
- 3With the ignition off, disconnect the TPS/PPS 'A' sensor connector. Using a multimeter, check for proper reference voltage (typically 5V) and ground at the connector terminals coming from the PCM. Then, test the signal wire for continuity back to the PCM. If reference voltage or ground is missing, trace the wiring back to the PCM for opens or shorts.
- 4If the sensor is a potentiometer type, measure its resistance across the terminals while manually moving the throttle blade or pedal. The resistance should change smoothly without any sudden jumps or drops, indicating a healthy sensor. Compare readings to service manual specifications.
Verify before repair
- - Replace the faulty Throttle Position Sensor (TPS) or Pedal Position Sensor (PPS).
- - Repair or replace damaged wiring and/or corroded electrical connectors in the TPS/PPS 'A' circuit.
- - Clean the throttle body bore and throttle plate if excessive carbon buildup is restricting smooth throttle operation.
- - Inspect and potentially replace the accelerator pedal assembly if the pedal position sensor is integrated and malfunctioning.
Vehicle-specific pages to check next
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