OBD-II Error Code P0939 - Transmission Control - Code 939

OBD-II Standard OBD-II Major Transmission Control

Model: SAE J2012 Standard | Code: P0939

Applicable Systems
OBD-II

Symptoms

The check engine light illuminates. The transmission may not engage properly, may slip, or default to limp-home mode. A transmission control system component has a malfunction.

Possible Causes

  • Faulty transmission gear ratio sensor
  • Input or output speed sensor circuit fault
  • TCC slip detection fault
  • Transmission internal clutch or band wear
  • Transmission control module calibration issue

Troubleshooting Steps

  1. Step 1: Connect an OBD-II scan tool and read all stored DTCs and freeze frame data
    All DTCs and freeze frame data are retrieved
  2. Step 2: Inspect the related wiring and connectors for the indicated system
    Wiring and connectors are in good condition
  3. Step 3: Use a digital multimeter to check sensor voltage, resistance, and continuity per manufacturer specifications
    Values are within specified range
  4. Step 4: Test the related actuator, sensor, or solenoid for proper operation
    Component operates within specification or fails definitively
  5. Step 5: Clear codes and perform a road test or drive cycle to verify repair
    Code does not return and system operates normally

How to Reset

To reset code P0939: 1) Repair the underlying fault. 2) Use an OBD-II scan tool to clear the DTC. 3) Perform a drive cycle to verify the monitor completes. 4) If the code returns, further diagnosis is needed. Caution: Do not clear codes without fixing the root cause.

Frequently Asked Questions

  • Q: What does OBD-II code P0939 mean?

    Code P0939 indicates: Transmission Control - Code 939. This is a SAE J2012 standard diagnostic trouble code related to Transmission Control.

  • Q: How serious is code P0939?

    Severity: Major. Immediate attention is recommended.

  • Q: Can I drive with code P0939?

    Not recommended - may cause further damage.

  • Q: How do I fix code P0939?

    Diagnose the Transmission Control system, check wiring and connectors, test related components, and replace faulty parts as needed.

Related OBD-II Standard Fault Codes

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Source: SAE J2012 Standard - Powertrain Diagnostic Trouble Codes

Category: OBD-II