P2138 on a Honda Accord is a diagnostic trouble code (DTC) that indicates a high input on the Throttle/Pedal Position Sensor/Switch “A” circuit. In practical terms, the car’s computer is seeing a higher-than-expected signal from the accelerator pedal position sensor (APPS) or throttle position sensor (TPS), or a mismatch between the two sensors. This can affect throttle response, idle behavior, and may illuminate the check engine light.
What P2138 means for a Honda Accord
In a Honda with drive-by-wire throttle control, P2138 points to an abnormal or high reading in the APPS/TPS A circuit. The engine control module (ECM/PCM) relies on a proper correlation between pedal position and throttle position. When it detects a high input on circuit A, it flags a potential sensor fault, wiring issue, or calibration problem that can alter throttle opening and engine response.
Common causes
Here are the typical sources of P2138 on a Honda Accord. The list covers problems that can occur alone or in combination.
- Faulty accelerator pedal position sensor (APPS)
- Faulty throttle position sensor (TPS) or a poor APPS/TPS correlation
- Damaged or corroded wiring, connectors, or grounding on the APPS/TPS circuits
- Loose or damaged harness connections near the pedal or throttle body
- Need for an ECU re-learn or software update after component replacement
- Aftermarket modifications or sensor miscalibration affecting throttle mapping
In many cases, the root cause is sensor or wiring issues rather than a pure software fault. A thorough inspection helps prevent misdiagnosis.
Common symptoms you might notice
Vehicles with P2138 may display one or more of the following symptoms. Not every symptom will appear in every case.
- Check Engine Light (CEL) or service light illuminated
- Poor throttle response, hesitation, or unexpected surges
- Erratic or high idle behavior
- Reduced engine power or limp-like mode in some driving situations
- Inconsistent accelerator pedal feel or apparent misalignment between pedal position and throttle opening
If you notice these issues, it’s wise to have the vehicle scanned and inspected to confirm P2138 and identify the exact fault source.
How to diagnose
Diagnosing P2138 involves confirming the code, inspecting hardware, and verifying sensor data with a scan tool. The following steps are typical for a Honda Accord diagnosis.
- Use an OBD-II scanner to confirm the code and retrieve any related DTCs (such as P2135–P2139)
- Check live data for APPS (pedal position) and TPS (throttle position) readings and compare their correlation as the accelerator pedal is moved
- Inspect the APPS and TPS connectors and wiring for corrosion, damage, or loose pins; ensure proper grounds
- Test sensors with a multimeter or scope as specified in the service manual; look for abnormal voltage ranges or non-linear behavior
- Inspect the throttle body, intake, and related vacuum lines for sticking or leaks that could skew readings
- If sensors or wiring appear faulty, replace the affected component and perform a relearn procedure if required by the vehicle
After performing repairs, erase codes and run a drive-cycle to confirm that the issue is resolved and that the APPS/TPS readings correlate properly.
Repair and maintenance options
The appropriate repair depends on the diagnosed cause. The following options cover common remedies for P2138 on a Honda Accord.
- Replace faulty APPS (accelerator pedal position sensor) or TPS (throttle position sensor)
- Repair or replace damaged wiring, insulation, or connectors on the APPS/TPS circuits
- Recalibrate or relearn the throttle/pedal position using a compatible scan tool or dealer tooling
- Check for available ECU software updates or recalls that address throttle/position sensor behavior
- Perform a thorough throttle-body cleaning if buildup is causing abnormal readings, followed by a relearn
If you’re uncertain about the relearn procedure, or if the code reappears after replacement, have a certified technician perform the diagnostic and calibration to ensure proper alignment between pedal and throttle signals.
Relearn and software considerations
Many Honda Accords with electronic throttle control require a throttle/ pedal position relearn after sensor replacement or battery disconnection. Using an appropriate scan tool, a dealer tool, or manufacturer-recommended procedure helps ensure the PCM correctly maps pedal input to throttle response. Always refer to the specific year and trim service manual for the exact steps.
Summary
P2138 on a Honda Accord signals a high input in the Throttle/Pedal Position Sensor/Switch “A” circuit, typically due to a faulty APPS or TPS, wiring problems, or a calibration/software issue. Diagnosis focuses on checking live sensor data, inspecting wiring and connections, and, if needed, replacing faulty sensors and performing a relearn. Addressing the fault promptly can restore proper throttle response and idle behavior, and prevent further drivability issues.