Updated: Feb 4
✔ This article has been fact checked.
A P0121 fault code stands for "Throttle Position Sensor (TPS) “A” Circuit Range Performance Problem", it's produced when the ECM detects that your throttle position “A” circuit’s output voltage has gone above or below the expected range.
P0121 is a sign of a severe problem and may cause a breakdown, avoid driving the vehicle if this code appears and fix as soon as possible.
If a DTC is associated to the powertrain, an OBD scanner will read it as starting with P, thus the letter "P". Generic fault codes are those of the format P0xxx.
Table of Contents:
The Meaning of a P0121 Fault Code
P0121 stands for Throttle Position Sensor (TPS) “A” Circuit Range Performance Problem, it is generated when the Engine Control Module (ECM) detects that your throttle position “A” circuit’s output voltage has either gone above or below the expected range.
Your TPS "A" Circuit, like your TPS "B" Circuit, has an anticipated output voltage range, when this fault code appears, it means that the output voltage of the throttle position "A" circuit has gone beyond or below the expected range for this sensor.
Is It Serious?
When the code P0121 is activated, your vehicle may enter failsafe mode (limp mode). Depending on your vehicle's failsafe mechanism, this might result in reduced speed or acceleration.
This issue might potentially cause your car to stall, lose power, or jerk forward. In certain situations, the vehicle may be unable to start or drive.
Signs & Symptoms
There are a few signs and symptoms associate with a P0121 code.
You may notice the following signs:
Check engine light (CEL) illumination
Jerking upon acceleration
Reduced speed and power
There are several potential causes for the P0121 error code, but the following are the most common.
An open or short circuit of the TPS circuit
Corrosion or damage to the wiring
Dirty or faulty throttle body
Loose connection of the TPS connector
Malfunctioning throttle position sensor (TPS)
Fixing the P0121 Trouble Code
Diagnosing this fault code is best done using a professional OBD scanner or by completing a diagnostic check with a skilled technician.
You may the following tools; a screwdriver for any clamps, a socket or ratchet set, a cloth, throttle body cleaner, OBD scanner.
Many vehicles with over 80,000-100,000 miles have sensor faults that arise during start-up or sustained driving.
Check to see if there are any technical service bulletins available for your vehicle's model and make sure to see if there is a known problem with your vehicle that may help you in resolving the issue.
Scan your system for any more OBD fault codes. If any of these are present, they should be investigated also.
Clear the error codes, start the vehicle and test drive it in a safe area while an OBD scanner scans the live data.
If the P0121 code is still present, examine the wiring for broken or loose connections. If any issues are found, repair or replace. If no issues are found, move on to the next step.
Clean the throttle body. If this does not resolve the issue you may need to replace the throttle body.
Cleaning the Throttle Body
Take the intake pipe out of the throttle body, spray throttle body cleaner onto a cloth. If you have a cable-operated throttle, pull the cable on the side of the throttle body to open it, or press on one side of the throttle plate to open it.
Wipe the carbon off the throttle plate and throttle body until they are completely clean. After cleaning the throttle body, you may need to have a throttle body relearn process completed in modern vehicles with electronic throttle bodies.
Always squirt throttle body cleaner onto a cloth, don't spray directly into the throttle body as this may damage electrical components.