Fault code P2123 – turbocharger boost control position sensor “A” circuit low

Fault code P2123 is called “Turbocharger Boost Control Position Sensor (TBCPS) “A” Circuit Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P2123

This Diagnostic Trouble Code (DTC) is a general powertrain code. The P2123 error is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P2123 – turbocharger boost control position sensor

The throttle position sensor (TPS) reacts to the movement of the accelerator pedal. It is a type of potentiometer. It converts the throttle position into a voltage output and sends a voltage signal to the engine control module (ECM). It also detects the opening and closing speed of the throttle and provides a voltage signal to the ECM.

When the throttle is closed, the signal from the position sensor is about 0.45 volts. If the TPS signal voltage approaches 5 volts, fault code P2123 is set. The control unit recognizes the problem as a high signal level in the throttle position sensor “D” circuit.

Simply put, the throttle position sensor is used to determine which position the throttle is in. If the signal value exceeds the normal upper limit, the PCM sets this code.

Symptoms of vehicle malfunctions

The main signal that an error P2123 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine light on the control panel will illuminate.
  2. Unstable or low idle speed.
  3. Increased engine rpm at idle speed.
  4. The engine stalls or starts poorly.
  5. The engine is not running evenly (pulsating).
  6. No reaction on gas pedal.

When the fault P2123 occurs, safe or emergency mode is activated, vehicle speed is limited to approximately 50 km/h. It is recommended to eliminate the problem as soon as possible.

Factors that can cause this error code

The error code P2123 can mean that one or more of the following problems have occurred:

  • Throttle position sensor circuit is open or bad electrical connection.
  • Throttle switch position sensor wiring harness is open or shorted to ground or other wire.
  • Throttle position sensor is defective.
  • Damaged computer (PCM).

How to fix or reset OBD-2 code P2123

Some suggested steps for troubleshooting and fix the error code P2123:

  1. Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances the error occurred.
  2. Clear the error codes from the computer memory and test-drive the vehicle to find out if the malfunction appears again.
  3. Visually inspect the electrical wiring and connections related to the throttle “D” position sensor for looseness and damage.
  4. Compare “A” and “D” throttle position sensors using a scan tool, and replace faulty sensor if necessary.
  5. Clear error code from computer memory again, test drive vehicle to see if problem is resolved.

Diagnose and repair of problems

Carefully check the throttle position sensor (TPS), wiring connector, and wiring for breaks, etc. Repair or replace if necessary to clear error P2123.

Check the voltage at the TPS (refer to your vehicle’s service manual for more information). If the voltage is too high, this indicates a problem. Replace the sensor if necessary.

If recently replaced, you may need to adjust the TPS. On some vehicles, the installation instructions require a proper adjustment (see the repair manual for details).

If there are no symptoms, the problem may be intermittent, and clearing the code may temporarily resolve it. If this is the case, you should definitely check the wiring to make sure it is not rubbing or frayed anywhere, etc.

On which vehicles does this problem occur most frequently

Fault code P2123 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Audi (A4)
  • Chery (Fora, Tiggo)
  • Chevrolet (Malibu)
  • Dodge
  • Ford (Focus)
  • GMC
  • Honda (Accord)
  • Hyundai
  • Kia
  • Mazda (3)
  • Mercedes-Benz (C300, Sprinter, Vito)
  • Nissan (Almera)
  • Opel
  • Peugeot
  • Subaru
  • Toyota
  • LADA (Granta, Kalina, Priora)
  • UAZ (Patriot)

Fault code P2123 can sometimes be found with other errors. The most common are the following: P2120, P2121, P2122, P2124, P2128.


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