P0120 OBD-II Trouble Code: TPS "A" Circuit Malfunction

check engine light logo

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?

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?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

More related articles

How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed Related Trouble Codes: P2441: EVAP Vent Valve Stuck Open EVAP trouble...

Related questions

Q: Car sputters in First or Second gear

The wet weather was a good hint toward an ignition misfire. The water will make the spark plugs and wires too short to ground. You would most likely be able to hear a snapping noise from the plug wires in...

Q: the car wont pass emmissions the code po420 comes up

Fault code P0420 indicates the catalytic converter is operating below proper efficiency. There are two oxygen (O2) sensors in the exhaust system. One just before and one just after the catalytic converter. The ecu reads the first O2 sensor to...

Q: Two injectors clogged

Hi. I know the injectors are expensive, but there is a lot of labor involved in their replacement. At the very least, they should be replaced one bank at a time, or all at once. A faulty injector will not...