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P0123: Throttle Position Sensor/Switch A Circuit High Input

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What is P0123?

Code P0123 is defined as ‘Throttle Position Sensor/Switch A Circuit High Input.’ Since it’s a generic powertrain code, it applies to all OBD-II equipped cars manufactured after 1996. 

DTC P0123 shows up when the Powertrain Control Module (PCM) or Engine Control Module (ECM) records an abnormally high output voltage reading in the throttle position sensor A. 

The throttle position sensor (TPS) is a type of resistor that changes its resistance value according to the opening angle or throttle position. The sensor is mounted on the throttle body (which controls airflow into your engine) and shaft that helps regulate the throttle valve position. 

When a reference voltage of 5 volts goes to the TPS, it sends a return voltage signal back to the PCM, depending on the throttle valve position. This information helps PCM decide the optimal ignition spark timing and fuel injection. Ideally, the TPS signal voltage should read around 4.5 volts at a wide open throttle. 

P0123 is set when the signal indicates an output voltage higher than 4.5 for more than 2 seconds.

If your car has Electronic Traction Control (ETC), the accelerator pedal position sensor helps measure how far you press the gas pedal. On some vehicles, the P0123 code can also occur if there’s a problem with the accelerator pedal position sensor instead of the throttle position sensor.

Some DTCs related to P0123:

  • DTC P0120 may indicate issues with your car’s throttle position sensor or accelerator pedal position sensor. 
  • DTC P0122 denotes a low output voltage below the expected throttle position sensor reading.

Common symptoms

Since the TPS is an essential part of the engine, the Check Engine Light turns on when there’s an abnormal voltage in the circuit. 

As soon as your Engine Control Module detects a problem, it goes into a failsafe mode to prevent further damage. This results in a closed throttle valve of less than 6 degrees of the throttle plate opening angle. 

The failsafe mode causes drivability issues, such as:

  • Hard start
  • Rough or high idle
  • Engine stalls or runs rough
  • Weak acceleration as the engine doesn’t receive the required air due to limited engine throttle.

The symptoms depend on your car manufacturer’s failsafe plan, which is a safety feature to prevent further damage to your engine.

Can I still drive?

It may be challenging to drive long distances as the car will go into a failsafe mode when code P0123 is detected, limiting your car’s performance. So your vehicle may have issues like rough idle or acceleration problems. 

You should have your vehicle reviewed by a mechanic and repair all issues before taking it out for a drive.

P0123 causes

A faulty throttle position sensor or an open, shorted connection at the TPS are some common causes of code P0123. Other causes include:

  • A defective throttle position sensor
  • A faulty accelerator pedal position sensor
  • Loose wiring or connections to the throttle/pedal position sensor
  • Circuit shorted to voltage issues in throttle/pedal position sensor
  • The TP sensor is not securely mounted
  • A dirty throttle body

Note: DTC P0123 can also show up if your powertrain control module has issues or need updates.

Diagnosis

Since DTC P0123 shows usual symptoms like a lit Check Engine Light or rough idle, a common diagnostic mistake is not doing a thorough component inspection before repairing or replacing any parts. 

It’s best to leave the diagnosis to a mechanic, as finding the exact cause of the P0123 trouble code could get tricky. Your mechanic may look into the following to figure out the issue:

  • First, they’ll use an OBD II scan tool and freeze frame data to review and duplicate the error code’s conditions. The mechanic may check the engine load, throttle position, road speed, and RPM.
  • The mechanic may check for shorted or damaged TPS connectors and wiring harness.
  • Then, they may compare the data between TPS circuit A and B on the scan tool. 
  • If the data is incorrect, the mechanic may conduct TPS pinpoint tests as per your car manufacturer’s recommendations.

Possible repairs for P0123 & Costs

Although the P0123 trouble code is easy to fix, it may require specific technical knowledge. So it’s best to let an expert mechanic do the job for you. 

Here are some ways the P0123 code can be fixed:

  • Repair TPS wiring or connector if they’re shorted. If the TPS wiring and connector are damaged, they should be replaced.
  • Replace the TPS sensor if it’s malfunctioning. Unplug the wiring harness connector from the throttle position sensor to replace it. After removing the harness connector, unbolt the sensor from the throttle body. Then, install the new sensor, and fix the wire that connects the main harness to the TPS. 

The cost of fixing it depends on what causes code P0123 and the labor charges in your area. If the TPS sensor needs to be replaced, the replacement cost may be around $157 and $202. This includes both labor charges ($55 – $69) and spare parts ($102 – $132.)

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