Error Code P2138 is defined as Throttle/Pedal Pos Sensor Voltage Correlation DTC. This means there’s a problem with throttle body’s ability to open and close properly.

This error code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

Definition

Error Code P2138 means that the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected a malfunction issue within the D and E circuits of the TP (throttle position) sensor.

As we depress the accelerator pedal, we push down a sensor that indicates the desired amount of throttle opening, which is then sent to the engine management computer (PCM). The computer then sends a voltage signal in response to the electric motor to open the throttle plate. Throttle Position sensor is embedded in the throttle body, converting the amount of throttle opening to a voltage signal to the computer.

The PCM monitors the correlation of both voltages. When both of the voltages agree, the system will work properly. When they deviate for two seconds, then the P2138 code will register, while simultaneously activating the Check Engine light.

In most cases, there are additional codes that accompany P2138, and a loss of control of throttle can be dangerous.

Other related error code includes:

  • Error Code P2135
  • Error Code P2136
  • Error Code P2137
  • Error Code P2139
  • Error Code P2140

Diagnostic steps for this code are all the same.

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:

  • Stalling when vehicle comes to stop
  • Lack of power or sudden loss of power at cruise speed
  • Stuck throttle at current RPM
  • No acceleration

Possible Causes

In most cases, the most common cause for this code is a poor connection in the connector or “pigtail” on the throttle body. Female terminals corrode or pull out of the connector.

  • Defective throttle body motor
  • Damaged connector or wiring associated with the throttle body motor
  • Defective TP sensor
  • Defective PCM
  • Defective electronic throttle body
  • Failed accelerator pedal or its wiring

How to Check

To diagnose for this code, mechanics back probe the accelerator pedal position sensor and the TP sensor using a scan tool or a multimeter to view the voltage output of each sensor. The voltage must be within the specifications set by the manufacturer.

They will also use the multimeter to test the ohm levels of the accelerator pedal position sensor and the TP sensor. Readings must be within the manufacturer’s specifications as well.

In most cases, mechanics use the TSB (Technical Service Bulletins) and recalls related to some makes and models for this code. They will also compare the make and model of the vehicle to its applicable recalls and TSBs to determine if there is one that has been implemented.

They will check online or in the service manual for possible relearn procedure to reset the computer.

If additional codes are present, these other codes must be addressed first since they are components in the system, and may be the direct cause of the P2138.

Technicians will check the connectors and terminals for signs of damages, such as corrosion.

They will also check the top cover of the throttle body for cracks or warping.

How to Fix

Replacement of one or both TP sensors

Replacement of the accelerator pedal position sensor

Repair of fault in a circuit (throttle position sensor circuit, accelerator pedal position sensor circuit) such as open, short, corroded wiring, or poor connection

 

Error Code P2138 is a serious problem, as sudden stalling while driving can be dangerous, especially for heavy traffic or turning.