P0123 code definition
Throttle Pedal Position Sensor/Switch (TPS) A Circuit High Input
What the P0123 code means
P0123 is the generic OBD-II code which indicates that the Engine Control Module (ECM) has seen the TPS circuit A output voltage go above the sensor's expected voltage specification range.
What causes the P0123 code?
- The TPS sensor circuit A range output to the ECM went above the specified voltage of 4.54 volts for more than 2 seconds, indicating a short in the sensor or wiring.
What are the symptoms of the P0123 code?
The Check Engine Light comes on and the ECM goes into failsafe mode by cutting current to the throttle actuator, causing the throttle valve to close to less than 6 degrees of plate 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 well 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.
How does a mechanic diagnose the P0123 code?
Scans and documents the codes received and views the freeze frame data to see when the code was set
Clears the OBD-II fault codes and re-tests the vehicle to see if the codes come back
Checks TPS connections and wiring for shorted or damaged wiring or connections
Compares the data between TPS circuit A and B on the scanner and if incorrect, performs the TPS pinpoint tests as per the manufacturer's recommendations
Repairs any wiring or connection shorts
Replaces the TPS as pinpoint test dictates, clears the codes, then road tests the vehicle
Common mistakes when diagnosing the P0123 code
Not visually inspecting connections and wiring first
Not scanning, documenting and clearing codes, then retesting for them to verify failures
Not verifying and repairing wiring or connector problems after sensor is replaced
Replacing the TPS sensor without making sure it is the problem
Not verifying whether the TPS sensor A and B circuit voltages are within specification before and after repair or replacements.
How serious is the P0123 code?
The P0123 code will cause the engine ECM to go into a failsafe mode, which will cause various drive issues until repairs are done. Depending on manufacturer's failsafe mode strategy, drive issues could include lack of acceleration, high idle, bucking or jerking, limited speeds, or stalling.
What repairs can fix the P0123 code?
Repairing or replacing the TPS connector for shorting
Repairing the wiring short as necessary
Replacing the TPS with a new sensor
Additional comments for consideration regarding the P0123 code
The P0123 code may be accompanied by other TPS codes, so following the manufacturer's pinpoint tests for each code received may be needed to find and fix the problem.
Most failures for code P0123 involve a defective TPS sensor, or a connector shorted internally.
All TPS codes will cause the ECM to go into the same failure mode; drive symptoms will be roughly the same.
Need help with a P0123 code?
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This article originally appeared on YourMechanic.com as P0123 OBD-II Trouble Code: Throttle Pedal Position Sensor/Switch (TPS) A Circuit High Input and was authored by Jay Safford.