The P2138 diagnostic trouble code (DTC) is a common headache for Nissan owners. This code indicates an issue with the correlation between the accelerator pedal position (APP) sensor and the throttle position (TPS) sensor, specifically a problem with APP sensor 2. This article delves into diagnosing and resolving a persistent P2138 and P2127 code on a 2013 Nissan Frontier with a 5.6L VK56DE engine swap from a Nissan Titan.
Understanding the P2138 Code in a Nissan
The P2138 code signifies a discrepancy between the signals from the APP sensor 2 and the TPS. The engine control module (ECM) detects a mismatch in the expected and actual throttle position, often leading to limp mode or reduced engine performance. In this specific case, the APP2 sensor reading drops to zero when the fault occurs.
Troubleshooting Steps Taken on a Modified Nissan Frontier
This particular case involves a Frontier with a Titan engine swap, including a custom intake manifold with a Nick Williams 102mm drive-by-wire (DBW) throttle body, upgraded injectors, and fuel pump. While the swap was performed using OEM components and a repinned harness, the intermittent P2138/P2127 codes persist.
Numerous troubleshooting steps have already been undertaken:
- Voltage and Signal Checks: All voltage validations, operational voltage changes, and APP/TPS sensor readings at the ECM have checked out according to the Nissan Factory Service Manual (FSM).
- Wiring Inspection: Meticulous inspection of the APP, TPS, and related wiring harnesses revealed no visible damage, abrasion, or loose connections.
- Component Replacement: The pedal assembly (containing APP sensors), throttle body (containing TPS sensors), and even the ECM have been replaced with new or known-good units.
- Grounding Enhancement: Existing grounds were cleaned and enhanced with additional 4GA grounding wires.
- EVAP System Check: The EVAP system was investigated, and the canister pressure sensor was replaced due to previous codes.
- Battery and Charging System: A new Odyssey Extreme AGM battery is in use and maintained with a CTEK charger, ensuring proper voltage supply.
Despite these efforts, the problem remains intermittent and difficult to reproduce on demand.
Potential Causes and Further Diagnostic Steps for P2138 Nissan
While many potential causes have been addressed, several areas warrant further investigation:
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Harness Connector Pins: Microscopic inspection of the connector pins themselves for any signs of bending, corrosion, or damage. A poor connection within the connector, even if visually undetectable, could be the culprit.
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CAN Bus Communication: Analyze the Controller Area Network (CAN) bus communication for any errors or dropouts that might be affecting signal transmission between the ECM and the sensors. A specialized scan tool with CAN bus monitoring capabilities would be necessary.
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DBW Throttle Body Compatibility: While the Nick Williams throttle body is reportedly used successfully on Titans, subtle differences in the Frontier’s ECM calibration or communication protocols might contribute to the issue. Consulting with Nick Williams or a specialist in Nissan engine swaps could provide insights.
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Intermittent Short or Open Circuit: An intermittent short or open circuit in the wiring harness can be extremely challenging to diagnose. Using a thermal camera to identify hot spots in the wiring or employing a continuity tester while manipulating the harness might help pinpoint the problem area.
Conclusion
Resolving a persistent P2138 code requires a systematic and thorough approach. While common causes have been addressed in this case, further investigation focusing on connector pins, CAN bus communication, and potential throttle body compatibility issues is recommended. Intermittent electrical faults can be particularly challenging to diagnose, requiring patience and persistence to pinpoint the root cause. Seeking expert assistance from a Nissan specialist or an experienced automotive diagnostician might be necessary to resolve this complex issue.
