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P0121 is a diagnostic trouble code (DTC) for "TPS "A" Circuit Range Performance Problem". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem
P0121 is a generic OBD-II code which indicates that the Engine Control Module (ECM) has seen the TPS sensor circuit A learned output voltage go above or below the sensor's expected range when compared to TPS sensor circuit B.
The TPS sensor circuit A learned range output to the ECM went above the specified voltage difference between TPS sensor circuit B by more than 1.6 volts
The TPS sensor circuit A learned range output to the ECM went below the specified voltage difference between TPS sensor circuit B by going less than .8 volts.
The ECM turns the Check Engine Light on and goes into a failsafe mode by cutting current to the throttle actuator to put the throttle valve to 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 and not accelerate as before.
Note: The symptoms are determined by the manufacturer failsafe ECM strategy for the vehicle during a failure and may vary between manufacturers and vehicles.
Scanning and documenting the codes received and viewing the freeze frame data to see when the P0121 code was set.
Clearing the OBD-II fault codes and retesting the vehicle to see if the P0121 code comes back.
Visually checks all TPS connections and wiring for any loose or damaged items.
Comparing the data between TPS circuit A and B on the scanner and if incorrect, performing the TPS pinpoint tests as per the manufacturer's recommendations.
Not following these simple steps:
Not conducting a visual inspection first
Not scanning, documenting, clearing or retesting for codes to verify failures
Replacing a TPS sensor before tests indicate a problem
Not comparing TPS sensor A and B specifications before and after repair or replacements
The P0121 code will cause the engine ECM to go into a failsafe mode, which will cause various drive complaints until repairs are done like lack of acceleration, high idle, bucking or jerking, limited speeds, or stalling, depending on manufacturer failsafe mode strategy.
The P0121 code may be accompanied by other TPS codes, so other repairs may need to be followed up with in order to have a complete fix.
Most failures for code P0121 are for a defective TPS sensor not tracking the throttle angle correctly.
All TPS codes will cause the ECM to go into failsafe mode.
The drive symptoms of all TPS codes will be roughly the same.
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