The Nissan P2138 diagnostic trouble code (DTC) indicates a problem with the Throttle/Pedal Position Sensor/Switch “D” / “E” voltage correlation. This essentially means the engine control module (ECM) detects an inconsistency between the signals from the accelerator pedal position sensor (APP) and the throttle position sensor (TPS). This article will delve into the P2138 code, particularly concerning Nissan vehicles, and offer troubleshooting steps based on a real-world case study.
Decoding the P2138 Code and its Symptoms
The P2138 code specifically points to a correlation issue between APP sensor 2 and TPS sensor 2. When this discrepancy arises, the ECM can’t accurately determine the driver’s intended throttle position. This often results in:
- Limp Mode: The vehicle enters a reduced power state to prevent damage.
- Check Engine Light: The malfunction indicator lamp (MIL) illuminates.
- Erratic Idle: The engine may idle rough or inconsistently.
- Poor Acceleration: The vehicle may hesitate or lack power during acceleration.
- Stalling: The engine may stall unexpectedly.
Case Study: A 2013 Nissan Frontier with a VK56DE Swap
A 2013 Nissan Frontier with a 5.6L VK56DE engine swap from a Nissan Titan experienced intermittent P2127 and P2138 codes. Despite a thorough swap ensuring 100% native compatibility, including a repinned harness, reprogrammed BCM, and updated ECM, the issue persisted. The vehicle would randomly enter limp mode, requiring an ECM reset or restarting the engine.
Troubleshooting Steps Taken and Potential Causes
Extensive troubleshooting was conducted, including:
- Voltage Validation: All voltage readings for APP1, APP2, TPS1, TPS2, and the 5V reference were within specifications.
- Wiring Inspection: Meticulous examination of the wiring harness revealed no damage, abrasion, or loose connections.
- Component Replacement: The pedal assembly (containing APP1 and APP2), throttle body (containing TPS1 and TPS2), and even the ECM were replaced with new or known-good units.
- Grounding Enhancement: Additional grounding wires were added to improve the electrical system’s grounding.
- EVAP System Check: The EVAP canister pressure sensor was replaced due to previous codes, but the P2138/P2127 issue remained.
Despite these efforts, the problem remained intermittent and difficult to reproduce. Possible causes for the P2138 code in this scenario, and in general, include:
- Wiring Harness Issues: Despite visual inspection, intermittent wiring issues within the harness, such as broken wires or poor connections, could be the culprit.
- Connector Problems: Corrosion or damage within the connectors for the APP or TPS sensors can cause intermittent signal disruptions.
- Sensor Malfunction: Even with new components, a faulty sensor can’t be entirely ruled out. Manufacturing defects occasionally occur.
- ECM Issue: Although a new ECM was tried, there’s a remote possibility of a compatibility issue specific to the engine swap configuration.
- Grounding Problems: While additional grounding was added, there might still be an underlying grounding issue not yet addressed.
Conclusion and Next Steps
The P2138 code indicates a serious issue that needs to be addressed to restore proper vehicle functionality and prevent potential safety hazards. While this case study highlights the complexities of diagnosing intermittent electrical problems, further investigation is needed. Recommended next steps include a more in-depth analysis of the wiring harness with specialized diagnostic tools, focusing on potential intermittent opens or shorts. Additionally, consulting with a Nissan specialist familiar with engine swaps might provide valuable insights. Resolving this issue requires a systematic and persistent approach to pinpoint the root cause.
