Skip the auto shop - Our mechanics make house calls

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

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

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!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...

Related questions

Q: Bad O2 sensor

I would ask for help from one of the mechanics at YourMechanic. They can come to your location and replace the faulty O2 sensor for you.

Q: Whilst driving the car will cut out. In the begining it would start immediatetly now if it cuts out it doesnt want to start

Hello. I would need to know the model of your Toyota to be able to give you the best information. From what you are telling me though it sounds like the crank sensor harness may be damaged or that one...

Q: When I rev it it has a hard time.

This is tough to diagnose without more info, however it could be potentially some things like a faulty mass air flow sensor or throttle position sensor. Either of these two parts will have a negative impact on fuel/air flow which...