P2138: TP Sensor/Switch D/E Voltage Correlation

What Is P2138?

DTC P2138 means “Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation.”

This diagnostic trouble code gets logged when the Powertrain Control Module (PCM) detects a problem in the voltage readings between a pair of throttle position sensors or accelerator pedal position sensors (AKA, gas pedal sensor) in your electronic throttle control (ETC) system.

So what does that mean?  

The accelerator pedal position sensor (APP sensor) is connected to the accelerator pedal and tells the PCM how far you’ve depressed the accelerator pedal. The PCM reflects pedal movement by moving the throttle plate open or close.

The throttle position sensor (TP sensor) is mounted on the throttle body. It provides feedback to the PCM on the position of the throttle plate (also known as the throttle valve.) This sensor sends a voltage signal to the PCM, indicating the exact throttle opening rate or the throttle angle.

Sensor pairs are used in both locations so that if one throttle position sensor or accelerator pedal position sensor fails, the other is still functioning.

If the PCM detects a voltage signal mismatch from either sensor pair, it’ll trigger the Check Engine Light and log the fault code P2138. In this situation, you may experience driveability issues.

Note: Most modern vehicles use electronic throttle control technology to determine the throttle angle or throttle response rate as opposed to the conventional throttle cable. Not only does the ETC offer better control over NOx emissions, but it also makes the vehicle more powerful while maintaining fuel efficiency.

Symptoms of a Failing Throttle/Pedal Position Sensor

With fault code P2138, you may encounter one or more of the following signs: 

1. The Check Engine Light Is On

An illuminated Check Engine Light on your dashboard could mean that your PCM has detected a TP or APP sensor malfunctioning that could affect your vehicle’s performance.

However, since the Check Engine Light could signify a host of engine issues, you’ll need an OBD2 scan tool to determine the actual problem.  

2. Trouble Accelerating

When the Powertrain Control Module or Engine Control Module (ECM) logs code P2138, you’ll experience difficulties accelerating your car.

This could be because the PCM receives conflicting information about the accelerator pedal and cannot determine the exact gas pedal position. As a result, there’s a delay or lack of response when you accelerate. 

3. The Vehicle Goes into Limp Mode

Your vehicle’s computer may enter limp mode when registering the fault code P2138. This safety feature protects you and your vehicle from dangerous situations.

When this happens, the Reduced Engine Power light may pop on your dashboard, indicating that your vehicle speed is limited. You may even experience other issues with the air-conditioning or gear system. 

4. A Sudden Loss of Engine Power

Sometimes, fault code P2138 may cause a sudden loss of engine power.

This issue occurs when the accelerator position sensor fails, forcing you to stop. When this happens, it’s best to consult a reputable mechanic to diagnose and fix the problem.

You’ll also notice the Reduced Engine Power light coming on.

Note: The P2138 code is a common issue with Acura, Subaru, Chevrolet, and Honda motor company vehicles.

Can I Still Drive?

The P2138 DTC is a serious problem that could cause several drivability issues.

So, if you notice the Check Engine Light on your dashboard and experience any of the mentioned symptoms, you should get your vehicle diagnosed for engine code P2138 ASAP. It’s also best to get it towed to prevent further damage.

What Causes a P2138 Code?

Here are all the potential causes of engine code P2138:

• Faulty throttle position sensor or accelerator pedal position sensor (gas pedal sensor)
• A bad throttle body actuator or accelerator pedal assembly
• Poor wiring connections or a bad wiring harness
• Incorrect dielectric grease used on the accelerator position sensor or throttle position sensor connector 
• A faulty sensor power supply circuit
• A malfunctioning Engine Control Module

How to Diagnose a P2138 Engine Code?

Diagnosing the fault code P2138 requires in-depth knowledge of critical components, including the wires, wiring harness, throttle position sensor, and accelerator pedal.

These components are extremely sensitive and prone to damage, so it’s best to hire a seasoned mechanic to diagnose the problem.

Here’s a brief look at how a skilled technician would diagnose trouble code P2138:

1. Begin the diagnostic process using an OBD2 scan tool to verify if the Check Engine Light on your dashboard was due to the fault code P2138.

2. Clear the existing engine codes and the Check Engine Light, and then take your vehicle for a test drive. If the trouble code P2138 and the Check Engine Light reappear, check the freeze frame data to pinpoint which APP sensor or TP sensor triggers fault code P2138.

3. Keep the engine running and lightly press the gas pedal, checking for drastic spikes or dips in the graph. If there are massive fluctuations in the data, the problem most likely stems from the pedal, not a sensor wiring issue.

4. Then, inspect the sensor connector and the wire, looking for any sign of damage or disconnection. Wiggle the wire to check for any changes in the graph, indicating a wiring issue or trouble with the APP harness connector.

5. Continue the inspection by checking the dielectric grease on the connector terminal (typically, your vehicle requires low-voltage dielectric grease.)

6. Check for a break in the sensor connector wire or the pedal connector terminals.

7. Finally, use a multimeter to inspect the circuit voltage.

What Are the Possible Repairs for P2138 & Costs?

Depending on the problem, your mechanic would need to either repair or replace the following components to fix fault code P2138:

• The wiring of the throttle body motor
• Throttle position sensor D or E or accelerator pedal position sensor
• Throttle valve
• Accelerator pedal assembly or harness connector
• Throttle body actuator

Repair costs

The repair costs for problem code P2138 may vary depending on the issue’s severity and the vehicle’s make and model.

That said, here’s the approximate cost for repairing the DTC P2138, including labor charges:

• Accelerator pedal position sensor: $150 to $200
• Throttle position sensor: $180 to $250
• Throttle body actuator: $600 to $700
• Wiring: $100 to $1000