If your Honda Pilot’s check engine light is on and the scanner shows code P2138, you’re probably looking for answers. Understanding the P2138 Honda Pilot code meaning is the first step to fixing the problem and getting back on the road safely.
This code points to an issue with your vehicle’s throttle or pedal position sensors. It’s a common problem that can cause drivability concerns. Let’s look at what it means, why it happens, and how you can address it.
P2138 Honda Pilot Code Meaning
Diagnostic Trouble Code (DTC) P2138 is defined as “Throttle/Pedal Position Sensor/Switch ‘D’/’E’ Voltage Correlation.” In simpler terms, your Honda Pilot’s Engine Control Module (ECM) has detected an implausible or conflicting signal between two of its throttle position sensors.
Modern vehicles like the Pilot use redundant sensors for critical systems like throttle control. This is a safety feature. The ECM constantly compares the voltage readings from these sensors. If the signals don’t match or correlate as expected—typically differing by more than a certain threshold—it triggers the P2138 code.
What Do the Throttle Position Sensors Do?
Your Pilot uses an electronic throttle control system, often called “drive-by-wire.” When you press the gas pedal, a sensor in the pedal assembly sends a signal to the ECM. The ECM then commands the throttle body to open a specific amount.
Inside the throttle body, there are usually two separate throttle position sensors (often called TP Sensor A and TP Sensor B). They act as a double-check system. One sensor’s voltage increases as the throttle opens, while the other’s voltage decreases. The ECM compares these two signals to ensure accuracy and safety.
Common Symptoms of a P2138 Code
You might notice several symptoms when this code is active. The most common ones include:
- Illuminated Check Engine Light (MIL): This is always the first sign.
- Reduced Power or Limp Mode: The ECM may limit engine power to protect the vehicle. You’ll feel a significant loss of acceleration.
- Poor Idle: The engine may idle rough, surge, or stall.
- Unresponsive Throttle: The gas pedal may feel sluggish or not respond correctly.
- Poor Fuel Economy: Incorrect throttle signals can disrupt the air-fuel mixture.
- In some cases, the vehicle may not accelerate past a certain speed.
What Causes the P2138 Code in a Honda Pilot?
Several issues can lead to the voltage correlation problem. Here are the most frequent culprits:
- Faulty Throttle Position Sensor (TPS): This is the most common cause. One of the sensors inside the throttle body has failed or is giving an erratic signal.
- Bad Accelerator Pedal Position Sensor (APP): The sensor in the pedal assembly could be malfunctioning, sending a bad signal to the ECM.
- Damaged or Corroded Wiring: The wiring harness connecting these sensors to the ECM can get damaged, pinched, or corroded, leading to poor signal transmission.
- Poor Electrical Connections: Loose, dirty, or corroded connectors at the throttle body, pedal sensor, or ECM can cause voltage issues.
- Faulty Throttle Body: Sometimes, the entire throttle body assembly may be defective, or the throttle plate mechanism could be sticking.
- Rarely, a Failed ECM: While less common, a problem with the engine computer itself could cause incorrect signal processing.
Is It Safe to Drive With a P2138 Code?
It is not recommended to drive your Honda Pilot for an extended period with this code active. The vehicle will likely be in a reduced-power “limp home” mode. This severely limits your ability to accelerate, merge, or pass, which can be a safety hazard on public roads.
Furthermore, the underlying issue could worsen, potentially leading to an unexpected stall. You should adress the problem as soon as possible. Have the vehicle diagnosed and repaired promptly.
How to Diagnose and Troubleshoot Code P2138
Fixing a P2138 code requires a systematic approach. You’ll need a basic set of tools and a reliable OBD-II scanner. Here is a step-by-step guide:
Tools You Will Need
- OBD-II Scanner
- Digital Multimeter
- Basic hand tools (screwdrivers, wrenches, etc.)
- Electrical contact cleaner
- Service manual for wiring diagrams (optional but helpful)
Step-by-Step Diagnosis
Step 1: Scan and Record Codes & Freeze Frame Data
Use your OBD-II scanner to confirm the presence of P2138. Clear the code and see if it returns immediately. If it does, the problem is current. Also, check for any other related codes (like P0122, P0123, P0222, P0223). Note the freeze frame data, which captures engine conditions when the code set.
Step 2: Perform a Visual Inspection
This is a crucial and often overlooked step. Carefully inspect the wiring harness and connectors at the throttle body and the accelerator pedal sensor. Look for:
- Burned, chafed, or broken wires
- Loose connectors
- Signs of corrosion or moisture
- Any damage from rodents
Step 3: Check Sensor Voltages
With the key in the “ON” position (engine off), use your multimeter to check the voltage signals. Back-probe the connectors for the throttle position sensor and the accelerator pedal sensor. Refer to your service manual for the exact pinout and expected voltage ranges. You should see smooth voltage changes as you slowly press the accelerator pedal. Any jumps, flat spots, or correlation errors between the two TPS signals indicates a fault.
Step 4: Clean Electrical Connections
If you find any dirty connectors, disconnect the battery first. Then, spray electrical contact cleaner on the connectors, let them dry, and reattach them firmly. This simple fix can sometimes resolve intermittent issues caused by poor contact.
Step 5: Test Sensor Resistance (if applicable)
Some sensors can be tested for resistance. Again, consult your manual for specifications. Measure the resistance across the sensor terminals and check if it’s within spec and changes smoothly.
Step 6: Further Testing
If the sensors and wiring check out, you may need to perform more advanced tests, like checking for reference voltage and ground signals from the ECM. A wiring diagram is essential here.
Common Fixes for the P2138 Code
Based on the diagnosis, here are the typical repairs:
- Repair Wiring: If you find damaged wires, solder and seal them properly. Replace entire harness sections if necessary.
- Replace the Throttle Position Sensor: Often, the TPS is integrated into the throttle body assembly. Many mechanics recommend replacing the entire throttle body as a unit to ensure reliability.
- Replace the Accelerator Pedal Position Sensor: The APP sensor is usually a separate component and can be replaced independently.
- Replace the Throttle Body: If the TPS is not servicable separately or the throttle plate is sticking, a new throttle body is the solution.
- ECM Replacement or Reprogramming: This is a last resort and should only be done after all other possibilities are exhausted. A dealership can perform a reflash, or in rare cases, replace the ECM.
Important Notes on Throttle Body Replacement
If you replace the throttle body, an electronic relearn or calibration procedure is almost always required. This allows the ECM to learn the new sensor’s closed and open positions. The procedure varies by model year. Sometimes it can be done with a specific sequence of turning the key and pressing the pedal. Other times, it requires a professional scan tool. Consult your repair manual for the exact steps for your Pilot.
Estimated Repair Costs
Costs can vary widely based on the root cause and whether you use OEM or aftermarket parts.
- Throttle Position Sensor (if separate): $50 – $150 for the part.
- Complete Throttle Body Assembly: $200 – $600+ for the part.
- Accelerator Pedal Position Sensor: $80 – $200 for the part.
- Labor: 1-2 hours of labor at a shop ($100 – $300). A throttle body replacement is usually straightforward.
- Total at a Shop: Expect a range from $250 for a simple sensor swap to over $1,000 for a dealer-performed throttle body and ECM relearn.
Preventing Future Issues
While some electronic failures are unpredictable, you can take steps to minimize risk:
- Keep the engine bay clean and address oil or coolant leaks promptly, as fluids can damage wiring and connectors.
- During routine maintenance, ask your technician to inspect visible wiring and connections.
- Use a quality fuel injector cleaner periodically to help keep the throttle plate clean from carbon buildup, which can affect movement.
- Avoid forcing the throttle plate manually, as this can damage the internal sensors.
FAQ Section
Can I clean my throttle body to fix a P2138 code?
Cleaning a dirty throttle body can fix codes related to airflow, but it usually won’t fix a P2138. This code is specifically about electrical signal correlation between sensors, not physical dirt. However, if the plate is so dirty it’s sticking, it could potentially cause secondary issues.
What is the difference between P2138 and P0122?
P0122 indicates a low voltage circuit problem with the Throttle Position Sensor. P2138 is specifically about a disagreement between two sensor signals. P0122 could be a cause that leads to a P2138, but they are distinct codes.
Will disconnecting the battery reset the code and fix the problem?
Disconnecting the battery will clear the code and turn off the light temporarily. However, if the underlying fault is still present, the code and check engine light will return within one or two drive cycles. It’s only a temporary reset, not a fix.
Do I need to go to a dealership to fix a P2138?
Not necessarily. A qualified independent mechanic with the right diagnostic tools can easily diagnose and repair this issue. The main advantage of a dealership is they have the latest software for ECM reprogramming if needed, which is rarely the case for this code.
Can a bad battery cause a P2138 code?
It’s possible but not typical. A weak battery or poor alternator output can cause low system voltage, which might lead to erratic sensor signals. It’s a good idea to have your battery and charging system tested if you’re experiencing multiple electrical gremlins.
Dealing with a P2138 code in your Honda Pilot can be frustrating, but it’s a manageable repair. By understanding the systems involved and following a logical diagnostic process, you can identify the root cause. Start with the simple visual checks, as they often reveal the problem. If you’re not comfortable with electrical testing, consulting a trusted mechanic is the best course of action to get your Pilot running smoothly again.