C1138: Gear Select Position Sensor Short to Battery
The C1138 code indicates a short to battery voltage in the gear select position sensor circuit. This fault is detected by the transmission control module (TCM) or all-wheel drive (AWD) control unit when the sensor signal voltage exceeds the expected range and reaches battery potential. The sensor provides the exact position of the gear selector, and a short circuit causes incorrect readings that can affect transmission shift logic and safety systems.
1. Commonly Affected Makes
2. Most Common Causes
- Short circuit in the gear position sensor wiring harness to a battery voltage source
- Internally damaged transmission range sensor (gear select position sensor)
- Corroded, bent, or pushed-back terminals in the sensor connector causing an electrical bridge
- Moisture or water intrusion in the sensor connector causing a temporary short
- Internal failure in the TCM or AWD control module affecting the sensor input pin
3. Symptoms You Will Notice
- Check Engine Light or Transmission Warning Light illuminated
- Erratic or incorrect gear selection, transmission stuck in a single gear or limp mode
- No start condition (starter interlock may prevent cranking if park/neutral not detected)
- Reduced fuel economy and drivability issues
4. Step-by-Step Diagnosis
Scan for codes and verify C1138 is present; check for related codes.
Visually inspect the gear select position sensor connector and wiring for damage, corrosion, or moisture.
Test the sensor signal circuit for voltage with key on; if voltage is near battery voltage (12V) when it should be lower, suspect a short to battery.
Disconnect the sensor and check for continuity between the signal wire and battery positive; if present, repair the short in the harness.
If wiring is okay, test the sensor resistance per manufacturer specs; replace if out of range.
If sensor and wiring are good, suspect a faulty TCM or AWD module; perform module diagnostics or replace as needed.
5. Frequently Asked Questions
Is it safe to drive?▼
No, driving with this code is not recommended. The transmission may not shift correctly or could fail to detect Park or Neutral, posing a safety risk. Have the vehicle diagnosed and repaired as soon as possible.
How much does it cost to fix?▼
The repair cost typically ranges from $150 to $600, depending on the cause. A simple wiring repair may cost $150-$250, while replacing the transmission range sensor can cost $200-$400. If the TCM or AWD module needs replacement, costs can exceed $600.