P2138: Everything You Need To Know

by Jordan Harris

Code P2138 signals that the vehicle’s computer receives confusing information about the accelerator pedal’s position. This can lead to problems and trigger the CEL (Check Engine Light) to come on. A warning light across your dashboard never means a good thing.

When your motor malfunctions, your vehicle’s computer will show a DTC to help you find the problem. You or your mechanic can use an OBD-II scanner to read the code. All car owners should consider buying this tool because it pays for itself in the long run.

This article discusses what error code P2138 entails and how you can approach this issue.

P2138 Code

Fortunately, DTC P2138 is not something that will take a lot of time to understand, as it is a generic drivetrain code. Experts call this code a generic one. That is because it applies to all models and makes of newer vehicles (made in 1996 and forward).

The Diagnostic Trouble Code P2138 stands for “Throttle/pedal position sensor/switch D/E voltage correlation.” This means an issue in the throttle that cannot open and close correctly. In the ’90s, car manufacturers started industry-wide productions of the throttle control technology “Drive by wire.”

This technology was made with the view to provide further control over emissions, traction, fuel economy, cruise and stability control, and transmission outputs. Before this, a basic cable controlled a vehicle’s throttle. It had a connection between the component and the gas pedal.


A throttle position sensor, also known as TPS, is located on the other end of the throttle linkage connection. You can find that on the throttle plate. The job of a TPS is to convert throttle position and movement into a voltage signal. Then to transmit it to the ECM, or engine computer, which receives the signals to create an engine control strategy.

An electronic throttle control technology comprises an electronically regulated throttle body fitted with an internal engine. Also an accelerator pedal position sensor and two ingrained throttle position sensors. That is for the engine management computer and correlation factors.

Throttle Pedal Position Sensor

Despite the code having the same frame of reference, the wording is different on a few automaker’s manuals. Such as the P2138 code Hyundai means “Electronic throttle control system malfunction power management.” While it stands for “Throttle position sensor circuit range/performance” on the Nissan unit, Infiniti.

When a driver pushes down on the accelerator pedal, they are pressing down on the sensor. The pushing indicates the required level of throttle opening. The signal sends itself to the ECM or electronic control module. In response, the electric motor receives voltage from the computer to open the throttle plate. 2 throttle position sensors attached inside the throttle body transform the throttle opening amount to a voltage signal for the ECM.

In most cases, the P2138 code does not come alone but with more additional codes. And a loss of throttle control can be dangerous.

Other associated error codes include:

  • P2135
  • P2136
  • P2137
  • P2139
  • P2140

A Deep Dive Into Accelerator Pedal Position Sensors

Accelerator pedal position sensors (APP sensors), otherwise known as throttle pedal position sensors, give the PCM/ECM information about drive throttle calls. The control module processes the information rapidly, aligning it with pedal movement by shifting the throttle plate.

A motor on the throttle plate opens and closes the throttle plate. It is powered both ways, so keep your fingers away from the throttle body. Check out the accelerator pedal position sensor wiring diagram here.

The throttle body also has a throttle position sensor (TPS) to provide feedback. The PCM/ECM needs a constant update on the throttle plate.


The driver’s perception of acceleration is virtually the same as if a cable aligned with a pedal to the throttle body plate. With properly operating electronic throttle control (ETC), that is. There is no need for cruise control parts on ETC-equipped vehicles. No idle speed control parts are needed – once again, ECM/PCM software handles it all.

Supplementary accelerator pedal sensors are needed to stop plausible runaway states, which would be bad. But a concern is that the 2 or 3 sensors will send out slightly different signals. This is how it is on every car.

Some cars feature a “mirrored” signal between the sensors. While others will have an increased voltage signal on one sensor and a decreased voltage signal on the other.

As a result, there is a difference between the 2 sensor signals for the detection of faults. The PCM/ECM would fail to know about the failed circuit or sensor if either of the two sensors failed. Or even if the sensor output wires shorted together. However, the fault can easily be detected when the sensor signals are different.

You can find the throttle position sensor/switch on the throttle body located on the intake manifold.

Bad Accelerator Pedal Position Sensor Symptoms

After knowing all this, you might be wondering, “What are the symptoms of a bad accelerator pedal sensor?” There is the most common sign of a failed accelerator pedal position sensor. That is the combination of a static accelerator pedal with an illuminated check engine light on the dashboard. Car owners may also notice high fuel consumption, shifting problems, and rough idle.

1. Slow Acceleration

This sign is easy to recognize as every driver eventually learns how their vehicle behaves when standing still or while driving. If you think your vehicle is displaying slow acceleration, the accelerator pedal sensor might be failing. In this case, we advise you to pull over as soon as you can and reach out to a mechanic. Poor pedal timing drastically increases the risks of a crash.

2. Rough Idle

The average RPM of a vehicle’s motor is between 600-700 rotations few minutes. The motor idles nicely at these RPMs without vibrating and uses lesser fuel. If your vehicle cannot idle smoothly, there may be a bad accelerator pedal sensor.

3. Car Does Not Accelerate Over A Particular Limit

Sometimes your accelerator pedal sensor cannot transmit positioning signals correctly. You’ll figure that out by monitoring if your vehicle can only accelerate to a certain point. If the car is not able to speed up, you know why.

4. Car Will Not Jerk Or Shift When Depressing The Pedal

A bad accelerator pedal sensor will give incorrect readings to the automatic transmission computer of the car. In these cases, the sensor is the culprit.

Sometimes, depressing it would relay delayed signals. A stream of different signals releases alternatively. The vehicle’s computer gathers and uses the mixture.

5. Low Gas Mileage

Your vehicle’s throttle position sensor may be at its failing stage. However, the impacts might not be obvious to you. The pedal could be giving a delayed response. But if you experience low gas mileage, the throttle position sensor may be working but not as great.

6. Check Engine Light

Modern vehicles come with a monitoring system across all the motor’s sensors. The Check Engine Light will light up if the engine control unit doubts that any sensors have failed. Or even if it sends out a wrong signal.

If the Check Engine Light is on, check the error codes with an OBD-II scan tool.

Follow this video guide to do accelerator pedal position sensor testing.

Accelerator Pedal Position Sensor Replacement Cost

On average, accelerator pedal sensor replacement costs between $100 and $300. It bases itself purely on the car’s make and model and labor costs. The part can cost around $50 to $200, whereas the labor cost will fall about $50 to $100 at an auto shop.

The cost varies greatly based on whether you replace the whole accelerator pedal or simply the position sensor. If you have to change the complete component, the price goes up. Remember that occasionally the new accelerator pedal position sensor has to be calibrated. That can be solely done with a diagnostic tool.

Symptoms Of Code P2138

Seeing troubling symptoms on your vehicle you suspect are leading to an active P2138 code situation? The prevalence of these signs usually differs from one case to another. But several of them are more common than the other. So what works for P2138 Nissan may not work for P2138 Chevy or P2138 Honda.

The following are a few of the most common indications of DTC P2138.

  • Lack of throttle response
  • Electronic throttle control light
  • Hesitation under acceleration
  • Stalling at different RPM ranges
  • Check engine light
  • Irregular or rough idle
  • Sudden loss of throttle response/power

Causes Of Code P2138

Much like the symptoms, the causes of error code P2138 vary depending on the make and model. The exact reason behind the error code can vary based on many unique variables. It may vary between two cars from the same lineup; P2138 Chevy Malibu and P2138 Chevy Silverado may not be the same.

However, the following is a list of the most common reasons for the P2138 error code:

Is Code P2138 Serious?

Diagnostic Trouble Code P2138 has proven to be a severe concern in almost every instance. DTC P2138 is linked to a working relationship between signals transmitted between a vehicle’s plate and throttle pedal. In simple words, this implies that the affected vehicle’s throttle body is answering the input weirdly. This can eventually lead to your vehicle accelerating and driving awkwardly.

Many drivability-related symptoms generally accompany error code P2138. It only takes one of these symptoms to leave a driver stranded in the middle of a road. This raises many safety concerns.

You have to diagnose the root of the error code at the first possible opportunity. With this, you are preventing further problems with your vehicle, but you are also saving money.

If you are dubious of your vehicle diagnosis skills, schedule an appointment at a good auto shop. In that way, you can get the issue diagnosed first.

Steps To Diagnose Code P2138

Using a code reader or scan tool, you have to figure out which APP sensor is causing the P2138 code.


Steps With Engine

  1. Keep the engine running with your vehicle in Park and softly press the gas pedal. Observe how the graph on the code reader/scan tool reacts to ensure the data does not spike or dip drastically.
  2. There is something wrong with that sensor if there is a dip or spike. You may find that the reason behind the malfunctioning sensor is dirt or bad contact. You will have to replace the pedal in this case.
  3. Some scan tools come with an option named “Agree or Disagree.” This lets you know if the data gathered from the two accelerator pedal position sensors agree. If you are using this scan tool and see the data does not match up, gently press the accelerator. In that way, you can see if there is a change. If the values change, understand that the problem originates in the pedal, not the sensor connections.
  4. Check the APP sensor wires and connectors for fraying, disconnection, damage, or the wrong kind of dielectric lubricant.
  5. Examine the APP sensor connector to ensure the connection is secure and check the sensor wires for any damage or frays. You can inspect the data forming in graphs as you move the wires to understand if the data varies. This would show a connector or wiring problem behind code P2138.
  6. Detach the connector to check it further, and look for corrosion at the ends. Double-check if the connector wires are loose or frayed by carefully tugging on them.

Steps With Dielectric Lubricant

  1. Look for dielectric lubricant on the connector terminal.
  2. The wrong kind of grease could be causing the problem. Just how grease for 12v instead of the actual 5v of the connectors wouldn’t be correct. You should only use low-voltage dielectric lubricant on this connector.
  3. Check for a short in the sensor connector wiring with a multimeter.
  4. Take a multimeter and change the meter dial option to ohms to inspect for breaks in the sensor connector wires.
  5. Using a multimeter, examine the pedal connector terminals and the sensor for bad or faulty wiring.
  6. For this step, keep the ignition off. For instance, a screwdriver takes off the covers from either connector using a small flat-edge tool. If one wire gives a significantly higher reading than the other, something is wrong. It means you should check the circuit immediately.
  7. To check bad circuit voltage, you can use a multimeter.
  8. For this, turn the multimeter dial to DC voltage from ohms. You want to rotate your key and bring it to the on position, but do not start the car. Also, keep the battery at 12v before this test. Charge your car’s battery first if the reading isn’t exactly 12v. This test should help you detect possible wire breaks that require fixing.

Common Mistakes When Diagnosing The P2138 Code

A common mistake people make when troubleshooting error code P2138 is replacing the throttle position sensor. And so they expect it to resolve all the issues. Although this is the most common reason for a vehicle storing DTC P2138, it is not the only cause. We recommend you always do a full inspection of your vehicle to find any electrical problems with that in mind. Make sure to inspect all the circuitry.

Can I Fix The P2138 Error Code Myself?


It is possible to resolve error code P2138 but you need to have prior car maintenance knowledge to do it right. The inspection and fixes could get challenging, and nobody should risk damaging their car. We recommend visiting a qualified mechanic for the job. One who can check the connections and wiring for any symptoms of damage.

From there, the professional will examine and potentially change any of these parts:

  • One or both TP sensors (Throttle position sensor D and/or Throttle position sensor E)
  • The accelerator pedal position sensor
  • Engine control module

They may also repair the error in the circuit like corroded, short, open wiring, or bad connection. They can repair circuits like accelerator pedal position sensor circuits, and throttle position sensor circuits.

How To Fix Code P2138

We have included a general template you can use to troubleshoot. Also to solve the primary reason behind the storing of DTC P2138. Before everything, consult the manufacturer-specific owner’s manual. You should do this before conducting any diagnosis or fix on your automobile.

1. Check For Additional DTCs

Before starting your diagnostic attempts, make sure you look for any other stored Diagnostic Trouble Codes. All other additional codes must be diagnosed and solved fully before moving to code P2138.

2. Inspect For TSBs

Automakers have released numerous technical service bulletins, explaining remedies for the P2138 code. This is particularly true for many Chevrolet SUVs/trucks. Those that showed bad signs of accelerator pedal position sensor failure in the past.

3. Visually Examine Throttle Body

Visually check the vehicle’s throttle wiring/body for signs of pinched/frayed wires. Check for any destruction to pins at any end of the throttle body connector. Try to find any damage done to the throttle body housing.

4. Relearn Throttle Body And Test

Move to the throttle body relearn process if you did not find any visual defects in step 3. This procedure is vehicle-specific. So you must refer to the manufacturer-specific service guide for this one. The method varies for trucks, cars, and SUVs. When finished, take your car for a test spin and see if code P2138 pops up again.

5. Inspect Voltage Sweep At Accelerator Pedal

If error code P2138 returns, peruse the affected car’s accelerator pedal with a multimeter. The car component has to have a probed back. You should get voltage readings between the ground and the signal circuit of the sensor.

Placing the car’s key in the “On” state, the signal voltage must be able to fluctuate smoothly between 0.5v and 5.0v. That is since the accelerator pedal depressed gradually. Changing this sensor will be required if the readings are too erratic.

6. Inspect Power At Throttle Motor

Lastly, back probe the motor’s power wire. It locates itself inside the throttle body wiring connector. Get a friend or family member to lightly brush the accelerator pedal, keeping the ignition on “On.” A voltage function would signal a problem with the throttle body. Whereas an absence of voltage reading would mean the PCM/ECM has gone bad. Or, it could also be an “open” state inside the corresponding signal unit.

Other Notes

Diagnostic trouble code P2138 is triggered if issues are with the vehicle’s throttle/pedal position sensor/switch. But, a DTC like this usually does not come alone. Error codes P2135, P2136, P2137, P2139, and P2140 also indicate problems with the same circuitry. Although seemingly similar and somewhat related, these codes tend to differ. They differ in their symptoms, possible causes, and solutions.

Estimated Cost Of Repair Of Code P2138

To resolve error code P2138, any repairs stated below may be needed. Keep in mind that you may need to repair or replace multiple parts. The estimated cost of repair given also includes the cost of relevant components.

  • Accelerator pedal position sensor: $130-$200
  • Throttle position sensor: $170-$230
  • Throttle body actuator: $570-$700
  • Wiring repair/replacement: $100-$1000

Bottom Line

When your vehicle shows any Diagnostic Trouble Code, you must get it checked immediately. Error code P2138 is not the worst and can get fixed without much issue. The estimated cost of repair is lower too. Get your vehicle properly inspected and repaired in time.

Frequently Asked Questions (FAQs)

How To Replace Accelerator Pedal Position Sensor

Replacing the APP sensor is not an easy job. Check out this video tutorial on it.

What Causes Code P2138

A damaged electronic throttle body can cause code P2138. Be it a faulty throttle position sensor, failing throttle pedal sensor, or damaged throttle body wiring/connector. Also, a bad ECM/PCM.

How Do I Fix Error Code P2138

You start by checking for shorts in the APP and TP sensor circuitry. Follow up on repairing any damage in the wiring or replacing the TP sensors.

What Does Code P2138 Mean

Code P2138 suggests that the Engine Control Module has found a problem in the D or E circuits of the TP sensor.

What Is Code P2138

Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation.

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