P2138 Code: Symptoms, Causes and Fixing

DTC (Diagnostic Trouble Code) is a car method of onboard diagnostic (OBD) computer system that tells you that there is a problem with your car. The onboard computer assigns a unique DTC code to each fault detected by the OBD computer system. P2138 is the most common diagnostic trouble code (DTC). This article explains the P2138 code symptoms and causes.

P2138 Code Definition

The P2138 code stands for “Throttle/Pedal Position Sensor/Switch “D”/”E” Voltage Correlation.”

What does the P2138 Code mean?

The P2138 code triggers when the powertrain control module (PCM) detects that the signals from the two throttle position sensors or the two accelerator pedal position sensors don’t correlate.

P2138 code

When this code triggers, the PCM can’t be sure of the actual accelerator position and will typically illuminate a warning light (wrench or throttle blade light, etc.) and limit throttle response to just under half throttle or, in extreme cases, the engine might not accelerate at all.

In modern vehicles, the new electronic throttle control technology consists of an accelerator pedal position sensor and an electronically controlled throttle body that pairs with an internal motor. Two embedded throttle position sensors also accompany this to infer correlation, and the PCM monitors the entire process.

When the accelerator pedal is depressed, a sensor sends the desired throttle opening to the PCM. In response, the computer sends a voltage reading to the electric motor to open the throttle plate.

Next, the two throttle position sensors embedded in the throttle body convert the amount of throttle opening to a voltage signal sent to the computer.

Finally, the computer monitors the correlation of both of these voltage readings. When the voltages agree, the system is operating as it should. However, when they deviate for two or more seconds, the PCM triggers the P2138 code to indicate a malfunction somewhere in the system.

P2138 is a common issue among the following makes: Chevrolet (especially on a Chevy Malibu), Nissan, Honda, Subaru, and Acura.

Causes of the P2138 Code

There are several potential causes of DTC P2138, some of which tend to be more common than others.

The following are the most common causes of P2138 code.

  • The damaged throttle position sensor
  • A defective throttle body motor
  • Damaged electronic throttle body
  • Damaged throttle pedal sensor wiring/connector
  • A damaged connector or wiring that is associated with the throttle body motor
  • Failing throttle pedal sensor
  • Bad Powertrain Control Module (PCM)

Read More: Symptoms of bad PCM

Symptoms of the P2138 Code

  • Illuminated check engine light
  • Hesitation under acceleration
  • Electronic throttle control light
  • Vehicle Stalling
  • Lack of throttle response
  • Sudden loss of power/throttle response
  • Starting issues
  • Rough or irregular idle

Read More: P0430 Symptoms and Causes

How To Diagnose and Repair Code P2138?

  1. Check to see if there are any other codes along with P2138 and clear your Check Engine Light with FIXD.
  2. Check the freeze frame data in order to pinpoint the issue.
  3. Check for Technical Service Bulletins (TSBs); if your manufacturer has had issues with this code, there may be a bulletin that will tell you what to replace.
  4. Check the wiring to the throttle body for chafing, disconnection, or pins that have backed out of the connector for the throttle body or throttle body position sensor.
  5. Check the wiring to the accelerator pedal position sensor for chafing, disconnection, or pins that have backed out of the connector.
  6. Inspect the throttle body motor and the throttle position sensor for proper function using the manufacturer’s recommended procedure.
  7. If all these check out good, consult your vehicle-specific service manual and perform a component inspection of the throttle body position sensor and accelerator pedal position sensor. This will usually have you check the signal voltage of the sensors. For the throttle position sensor, it should start at approximately .5V and go up to 5V or vice versa, based on which sensor you’re testing. The accelerator pedal position sensor will start with a low voltage and increase the voltage as the pedal is depressed.

Common P2138 Code Diagnosis Mistakes

  1. When diagnosing the P2138 trouble code, an easy mistake would be to have the throttle position sensor replaced and ‘hoping’ it fixes the problem.
  2. Replacing the throttle body without checking for poor wiring or loose connections.

 Repair Cost of P2138 Code

The estimated repair cost of the P2138 code includes the cost of the relevant parts and the labor required to make the repair.

  • Wiring repair/replacement: $90 to $1100
  • Throttle body actuator: $560 to $710
  • Accelerator pedal position sensor: $120 to $220
  • Throttle position sensor: $160 to $240

FAQ Section

How Serious Is P2138 Code?

The P2138 code is considered to be serious. This is due to the fact that DTC P2138 is associated with the working correlation between signals from a vehicle’s throttle pedal and throttle plate.

This trouble code can cause the vehicle to lose its throttle response. If this happens at the wrong time, it could result in a wreck. Immediate repair is the only recommendation.

Can I drive with a P2138 Code?

It is not recommended to drive your car with the P2138 code as it can impair your ability to control your car’s acceleration.

This can be very dangerous on the road and even lead to potential accidents and damage to your vehicle and others. This is why you should immediately take your car to a certified service station when confronted with the P2138 code.

What repairs can fix the P2138 code?

  • Replacing the throttle body motor or throttle body assembly
  • Repairing or replacing wiring that is associated with the throttle position sensor
  • Repairing or replacing wiring that is associated with the throttle body motor
  • Replacing the throttle position sensor
  • Replacing the Powertrain Control Module
  • Reprograming of the PCM

How easy is it to diagnose a P2138 Code?

The first step in diagnosing the P2138 code issue is visually inspecting the throttle body, the throttle body motor, and the throttle position sensor.

A qualified technician will then examine the system for any circuitry issues related to the wiring and the connectors. They will then test the throttle body motor and the throttle position sensor to ensure they are correctly functioning by following the manufacturer’s recommended process. Finally, the technician will test the ECM to ensure it is working correctly.

How do you reset a throttle pedal position sensor?

The easiest way to reset your throttle position sensor is to unhook the negative cable from your battery for up to five minutes or to remove the fuse for your engine control module.

Will disconnecting the battery reset the throttle position sensor?

You can reset your throttle position sensor by disconnecting the battery and then reconnecting it after a few seconds. This will clear any codes that may be stored in the computer and allow the sensor to relearn its idle position.

How do I calibrate my accelerator pedal position sensor?

To recalibrate the PCM and accelerator pedal, the ignition switch must be in the ON position, and then the accelerator pedal must be slowly and fully depressed from idle to full throttle. Repeat the procedure three times.

How much does it cost to fix TPS?

The average replacement cost for the throttle position sensor (TPS) is between $100 and $230. The parts cost is between $60 and $120, while the labor cost is between $30 and $120.

What happens if you don’t reset the throttle body?

If the TPS is causing your ECM to think that the throttle is closed when it isn’t, it’ll reduce the amount of fuel in the air/fuel mixture and cause the engine to run lean. Without enough fuel in the mixture, the engine will fail to make as much power as it normally does.

Is the throttle position sensor the same as the accelerator pedal position sensor?

No, they are not the same. The throttle position sensor is located inside or on the throttle body of the engine. The accelerator pedal position sensor is located on the accelerator pedal inside the car.

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