Comprehensive diagnostic guide for OBD-II code P0931

Important Notes

• What P0931 is (scope): OBD-II "P0" codes are powertrain codes. Wikipedia's OBD-II pages explain that powertrain codes cover engine and transmission control-related issues and are part of the broader family of diagnostic trouble codes (DTCs) used by modern vehicles. This establishes that P0931 is a powertrain/transmission-related code, but the exact OEM-definition of P0931 is not spelled out in you supplied.
• A provided Open Source mapping for P0931: An OSS definition in Portuguese notes translated roughly as )
• Practical caution: Because OEM meaning can vary by maker and model, always confirm the exact P0931 definition for the specific vehicle using the factory diagnostic/definition (OEM service information). here provide general context only; the OSS mapping provides one specific interpretation.

Symptoms

• Malfunction indicator lamp (MIL) illuminated or a persistent check engine light.
• Vehicle may fail to shift, engage, or release the shift lock/solenoid, or exhibit intermittent shifting problems (depends on transmission type and control wiring).
• Interlock issues: difficulty moving the shifter out of Park or into required gears; possible locking/unlocking symptoms with the shift lock mechanism.
• Transmission warning messages or code readouts related to the shift lock solenoid or transmission control may accompany the P0931 code.
  Note: Actual symptoms vary by OEM, model year, transmission type, and how the shift lock solenoid/lock mechanism is integrated with the vehicle's PCM/TCM.

Probable Causes

• Primary suspect (electrical/electronic fault in the shift lock circuit): High likelihood that the shift lock solenoid circuit, wiring, connector, or the PCM/TCM output that drives the solenoid is at fault. This aligns with the OSS mapping that P0931 relates to a "high signal" condition on the lock solenoid and with general powertrain electrical fault patterns.
• Secondary suspect (control module/ECU output issue): The PCM/TCM control output that commands the solenoid could be faulty, misconfigured, or misreading a sensor input, causing an erroneous high signal.
• Interlock/safety switch or gear position sensing issue: The park/neutral safety switch (or equivalent, depending on the vehicle) might report an improper gear/lock state to the PCM, causing the solenoid logic to behave unexpectedly.
• Mechanical lock/solenoid binding or mechanical interference: A physical binding of the shift-lock mechanism or a stuck solenoid can produce a persistent or intermittent "signal" condition that triggers the code.
• Wiring harness damage or corrosion: Damaged or corroded wires/connectors in the shift lock solenoid circuit can create false signals or open/short conditions.
• Less common: software/firmware issue in the PCM/TCM, or cross-coupled fault with other transmission control signals.

High-level diagnostic plan (step-by-step workflow)

1) Confirm and document

• Use a reputable scan tool to confirm P0931 is present and capture freeze-frame data and any related codes (P0xxx family codes that may accompany P0931).
• Note vehicle make/model/year, transmission type, fuel, and any recent work (modifications) that could affect solenoid wiring or control signals.

2) Visual and environmental checks

• Inspect shift-lock solenoid wiring harness, connectors, and grounds for corrosion, bent pins, damaged insulation, or loose connections.
• Check for obvious damage in the area of the shift lock solenoid and the lock mechanism.
• Inspect fuses/relays related to the shift lock solenoid or transmission control circuits.

3) Electrical tests on the shift lock solenoid circuit

• Confirm power supply to the solenoid circuit. With the ignition on (and engine off, if safe), verify presence of designated supply voltage at the solenoid connector when the solenoid is commanded (or at least when the unlock/lock cycle is initiated by the PCM).
• Check ground path: verify a solid ground at the solenoid's ground pin; perform a continuity check to chassis ground.
• Resistance/coil test: with the circuit disconnected, measure the solenoid coil resistance and compare to typical expected resistance (note: exact values vary by vehicle; refer to service information for the exact spec). A coil that is open or shorted will indicate a faulty solenoid.
• Signal integrity: monitor the PCM output that commands the shift lock solenoid (using a scope or a logic probe if available) to see if the PCM is delivering a proper control signal when the system expects to lock/unlock.
• Inspect for voltage drops: with the solenoid energized, check for excessive voltage drop across supply/ground, which could indicate poor wiring or corroded connections.

4) Interlock and sensor checks

• Park/Neutral safety switch (or gear position sensor): verify that the switch or sensor reports proper Park/Neutral status to the PCM. A misreported gear state can cause the PCM to output a fault signal to the solenoid.
• Timing and sequencing: ensure the order of operations (brake pedal input, ignition state, gear position) aligns with the vehicle's design. Faulty sequencing or a failed braking signal can affect lock solenoid control behavior.

5) PCM/TCM/ECU and software considerations

• Check for other related transmission codes or software/firmware advisories. In some cases, a reflash or software update from the OEM can resolve control faults affecting solenoid operation.
• If no electrical faults are found and software is up to date, consider the possibility of a PCM/TCM fault or intermittent control issue; consultation with the OEM service information is advised before replacing modules.

6) Mechanical assessment

• If electrical and sensor tests appear sound, inspect the physical shift-lock mechanism for wear, binding, or mechanical interference that could cause abnormal solenoid loading or misleading signals to the PCM.

7) NHTSA/vulnerability data note

8) Functional test and verification

• After any repair (solenoid replacement, harness repair, ground/connection fix, or sensor replacement), clear the codes and perform a road test or functional test as appropriate for the vehicle.
• Recheck for P0931 and any related codes; verify proper shift-lock function by attempting the normal lock/unlock sequence and gear selection.
• Confirm there are no abnormal symptoms, such as hard shifts, failed to shift events, or reappearance of the code.

What a repair might involve (practical actions)

• Replace suspected faulty shift lock solenoid if electrical test results indicate coil or internal failure.
• Repair or replace damaged wiring harness or connectors to the shift lock solenoid; fix grounds and clean corrosion.
• Replace or repair Park/Neutral safety switch or gear position sensor if confirmed faulty.
• Update or reflash PCM/TCM software if a known software fault relates to solenoid control in the vehicle's OEM service bulletin.
• If a mechanical binding issue is found, service/repair or replace the shift-lock mechanism components, ensuring proper lubrication and clearance as designed by OEM specifications.
• After any repair, perform a thorough retest including code clearing and road test to ensure P0931 does not return.

Safety Considerations

• Disconnect the battery before servicing electrical components in the shift-lock/solenoid area when required by service procedures.
• Use proper PPE, be mindful of airbag/system implications if near other harnesses, and ensure vehicle is secured (handbrake engaged, wheels chocked) when performing tests.
• Work in a well-ventilated area and follow all shop safety and vehicle manufacturer guidelines.

Summary and OEM cautions

• P0931 is a powertrain (transmission-related) code. in the supplied Wikipedia pages, so confirm the precise meaning for the vehicle with OEM service literature.

• Probable causes are predominantly electrical (solenoid circuit, wiring, ground, PCM control) with mechanical or sensor issues as secondary factors. This aligns with typical powertrain code behavior but can vary by vehicle.

• Wikipedia - OBD-II: Diagnostic Trouble Codes and Powertrain Codes: establishes that OBD-II codes are used for powertrain issues and that P0x codes are powertrain related (general context for P0931 being a powertrain code).

• Open Source code definitions: one entry maps P0931 to )

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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