P0120 code definition
Throttle Pedal Position Sensor/Switch (TPS) "A" Circuit Malfunction
What the P0120 code means
P0120 is the generic OBD-II code which indicates that the Engine Control Module (ECM) has seen the TPS sensor circuit A output voltage going below or above the sensor's expected range, or is chattering when compared to TPS sensor circuit B.
What causes the P0120 code?
The ECM detected that the output from TPS sensor circuit A went outside of the specified voltage range in relation to TPS sensor circuit B.
The TPS sensor circuit A output falls below .2 volts or goes above 4.5 volts.
What are the symptoms of the P0120 code?
The ECM turns on the Check Engine Light and goes into failsafe mode by cutting the current to the throttle actuator to put the throttle valve at approximately less than 6 degrees opening.
The ECM controls fuel injection and timing to control engine speeds.
The vehicle would be able to be driven very slowly with limited throttle response.
The engine may idle higher than normal, but will not accelerate properly.
Note: The symptoms are determined by the manufacturer failsafe ECM strategy for the vehicle during a failure and may vary between manufacturers and vehicles.
How does a mechanic diagnose the P0120 code?
Scans and documents the codes received and views the freeze frame data to see when the code was set
Resets the codes to clear the OBD-II fault codes and retests the vehicle to see if the code comes back
Visually checks all of the TPS connections and wiring for any loose or damaged items.
Compares the data between TPS circuit A and B with a scanner, and if incorrect, replaces the TPS as directed by the pinpoint testing.
Common mistakes when diagnosing the P0120 code
Not performing a visual inspection first
Not scanning, documenting, clearing, and retesting for codes to verify failures
Not replacing an TPS sensor when tests indicate a problem
Not comparing TPS sensor A and B to be within specification before and after repair or replacements
How serious is the P0120 code?
The P0120 code will put the engine ECM to go into a failsafe mode, which will cause various drive complaints until repairs are done. For example, lack of acceleration, high idle, bucking or jerking, limited speeds, and possible stalling depending on the manufacturer failsafe mode strategy.
What repairs can fix the P0120 code?
- Repairing or replacing the TPS connector
- Repairing the wiring as necessary
- Replacing the TPS with a new sensor
Additional comments for consideration regarding the P0120 code
The P0120 code may be accompanied by other TPS codes, so following the manufacturer pinpoint tests for each code received may be needed to fix the complaint.
Most failures for code P0120 involve a defective TPS sensor not tracking the throttle angle correctly.
All TPS related codes will enable the failsafe mode and cause the same drive symptoms.
Need help with a P0120 code?
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This article originally appeared on YourMechanic.com as P0120 OBD-II Trouble Code: TPS "A" Circuit Malfunction and was authored by Jay Safford.