P2138 Code: How-To Guide And A Video To Diagnose And Fix It Like A Mechanic

p2138 code
Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation

Your Check Engine light is on and you’ve got a code P2138, “Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation.” What does that mean? In this video, our mechanic breaks down the P2138 code, its symptoms, including poor acceleration and reduced power mode, and shows you how to diagnose the potential causes so you know what to do to clear the code.

Watch now: 

Check Engine Light? Weak Acceleration or Reduced Power – Code P2138 

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What is code P2138 and what does it mean? 

Code P2138 is an accelerator pedal position (APP) sensor or throttle position (TP) sensor code. In simpler terms, it’s an OBD2 code triggered when one of the two sensors in your gas pedal malfunctions. 

As our mechanic explains in the video above (1:07), a gas pedal has two APP (Accelerator Pedal Position) sensors to essentially serve as fail-safes for each other in case one triggers an error code. He uses an OBD-II scan tool to look at the data for both sensors to see whether the sensors are working normally. It’s important to know that these sensors won’t reflect exactly the same data, but each sensor’s data needs to correlate with the other’s and fall within a certain range. You can see if the data correlates by watching it on your scan tool as you press the gas (with your car parked, of course). If you see a large spike or dip from one sensor, then you’ll know which sensor is triggering the P2138 code. 

Can I drive with P2138, or is it too serious? 

We recommend addressing the issue causing P2138 as soon as possible. Your car may have trouble accelerating or go into reduced power mode when this code is triggered, which lets you know it’s not the best idea to drive with P2138. 

What are typical P2138 symptoms? 

P2138 code symptoms can include: 

  • Your Check Engine light is on. 
  • You’re having difficulty accelerating. 
  • Your Engine Reduced Power light may come on. This basically means your car’s computer (powertrain or engine control module) has put your car into a safe mode to reduce heavy acceleration or fast speeds since code P2138 was triggered. 

What causes a P2138 code? 

P2138 causes can include: 

  • A failing, faulty, or dirty APP or TP sensor 
  • A faulty, bad, loose, or disconnected APP or TP sensor connector 
  • Faulty or damaged APP or TP sensor wiring or circuits 
  • Incorrect dielectric grease used on the APP or TP sensor connector 
  • A computer issue 

How do I diagnose P2138? 

  1. Use a scan tool or code reader that graphs data to determine which APP sensor is triggering P2138 

With the engine running and your car in Park, lightly press on the gas, and watch the graph on the scan tool to make sure the data doesn’t dip or spike drastically (1:59 in the video above). If there is a spike or dip, you’ll know there’s something wrong with that particular sensor. You may find the sensor isn’t working correctly because it’s dirty or has bad contact, in which case the pedal itself will need to be replaced. 

Certain scan tools have an option called “Agree or Disagree,” which lets you know whether the data from the two APP sensors “agrees.” If you use a scan tool with this option and see before trying anything else that the data disagrees, from there, gently step on the accelerator and watch for a change in the data. If the data changes, that indicates the issue is stemming from the pedal itself and not the sensor wires. 

  1. Inspect the APP sensor connector and wires for damage, fraying, disconnection, or the wrong type of dielectric grease 

Check the APP sensor connector to make sure it’s tightly connected and inspect the sensor wires for any frays or other damage (2:54). You can also watch the data being graphed while you wiggle the wires to see if the data changes, which would indicate a wiring or connector issue is triggering P2138. 

Disconnect the connector (3:13) to further inspect it, checking for any corrosion in the terminals, and if any of the connector’s wires are frayed or loose, which you can double-check by gently tugging on the wires. 

Also check for any dielectric grease on the connector terminal. If the incorrect kind of dielectric grease were used, such as grease for 12 volts rather than the connector’s 5 volts, that could be causing the issue. Only low-voltage dielectric grease should be used on this connector. 

  1. Use a multimeter to test for a break in the sensor connector wiring 

Use a multimeter and move the meter dial to the ohms option (our mechanic describes it as looking like a little horseshoe) to test the sensor connector wires for a break that could trigger P2138. Our mechanic shows you how to do this in the video above, at 4:03. 

  1. Use a multimeter to test the sensor and pedal connector terminals for faulty or bad wires 

With the ignition off, first, use a small flat-edge tool, like a screwdriver, to remove the covers from both connectors (5:11). Our mechanic shows you how to use a multimeter to test the APP sensor and pedal connector terminals beginning at 5:36. If one wire reads significantly higher than another, that indicates that something is wrong, and you’ll want to inspect that circuit. 

  1. Use a multimeter to test faulty circuit voltage 

To test a circuit, switch the multimeter dial from ohms to DC voltage. You’ll want to turn your key to the on position for this test, but don’t start your car. Also make sure your battery is at 12 volts before doing this test. If it’s not at 12 volts, make sure you charge it first. Our mechanic walks you through how to do this test beginning at 7:00, which should help you find potential wire breaks that need to be addressed. 

How do I fix P2138? 

Depending on the problem you identify as the cause of the P2138 code after completing any of these tests, you’ll need to repair or replace the problematic part(s) (e.g. Replace the accelerator pedal or one of the connectors, or repair faulty wires). 

Video: How To Replace Accelerator Pedal & Position Sensor

Then you can clear the P2138 code. 

P2138 Code
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Optional tools for diagnosing code P2138: 

  • Scan tool with “Agree or Disagree” option and graphing ability 
  • Multimeter 
  • Flat head screwdriver 

Need other parts mentioned in this article? Shop now: 

  • Accelerator pedal position sensor (APP)
  • Throttle position (TP) sensor

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Article Name
P2138 code – Diagnose and Fix It Like a Mechanic – 1A Auto
Our mechanic breaks down the P2138 code (“Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation”) and shows you how to diagnose and fix it.
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1A Auto
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