C1138 — Gear Select Position Short to Battery #

Please note: The wording of this code may vary depending on your vehicle manufacturer (OEM). Always refer to OEM service information for your specific model.

• Gear Selector Position Circuit Short to Battery (Nissan)
• Transmission Range Sensor Circuit Short to B+ (Ford)
• Shift Lever Position Circuit Shorted to Voltage (Mazda)

Summary of DTC C1138 #

DTC C1138 indicates a fault detected by the vehicle’s control module involving the gear select (or shift) position sensor circuit. This sensor tells the car’s computer which gear is selected. The “short to battery” part means the circuit is receiving a higher voltage than expected, likely due to an unintended connection to battery voltage. This prevents the control module from reliably detecting the shifter’s position, which can affect transmission logic and may trigger warning lights or limit driveability. While not always resulting in immediate breakdown, the code should not be ignored, as it can point to underlying wiring or sensor issues.

Common Symptoms for Code C1138 #

When C1138 is present, drivers or technicians may notice several telltale signs. The most prominent is usually a warning light on the dashboard (such as a transmission or check engine light). The vehicle may also enter a “limp home” mode, restricting gear shifts to protect the transmission. Occasionally, the transmission may not shift at all, or incorrect gear indication may appear on the instrument cluster, leading to confusion or even unsafe driving situations.

• Transmission or check engine warning light illuminated
• Inability to shift gears or delayed shifting
• Incorrect gear displayed on dashboard
• Limp mode activation (reduced performance)
• Poor fuel economy due to improper gear usage

Most Likely Causes for Code C1138 #

The causes of a C1138 code are primarily related to electrical faults in the gear select circuit. The most frequent issues are wiring-related, but sensor or connector faults are also common. Here’s a breakdown by likelihood:

1. Damaged or shorted wiring in the gear select sensor circuit (wires rubbed through, pinched, or corroded)
2. Faulty gear select/shift position sensor (internal short to power)
3. Corroded or loose connector at the sensor or module
4. Incorrectly installed aftermarket electronics tapping into the circuit
5. Water intrusion into the transmission harness or module area
6. ECU (Engine Control Unit) or TCM (Transmission Control Module) internal fault (rare)

Step-by-Step Diagnosis for C1138 #

A systematic approach is key to diagnosing C1138. Always start with the basics and work toward more complex causes, using OEM wiring diagrams and a quality digital multimeter.

• Verify the presence of the code and note any additional DTCs.
• Inspect the gear select sensor circuit wiring for visible damage, rubbing, or pinching.
• Check all connectors for corrosion, bent pins, or signs of water ingress.
• Using a multimeter, check for battery voltage on the gear select sensor signal wire (should not be present).
• Disconnect the sensor and check whether the voltage disappears (isolating a short in the harness or sensor).
• Test the sensor’s resistance and continuity per OEM specifications.
• If wiring and sensor check out, test the TCM/ECU input for shorts or internal failure.
• Clear the code and test drive to confirm repair.

Possible Repairs for C1138 #

Repairs should always address the root cause identified during diagnosis. The most successful fixes for C1138 include:

• Repairing or replacing damaged wiring in the gear select circuit
• Replacing the faulty gear select/shift position sensor
• Cleaning or replacing corroded connectors, applying dielectric grease
• Rerouting or shielding wires from aftermarket electronics interference
• Sealing or repairing water intrusion points
• In rare cases, replacing the TCM/ECU after all other causes are ruled out

Is It Safe to Drive with Code C1138? #

Driving with code C1138 is generally not recommended. While the vehicle may move, issues with gear selection can cause unpredictable shifting or leave you stuck in a single gear. This could be dangerous in traffic or on the highway and could also cause further damage to the transmission. If the vehicle enters limp mode, speed and power will be severely limited. It’s best to have the issue diagnosed and repaired before regular driving.

Vehicles Most Commonly Affected by C1138 #

C1138 is most frequently reported on the following vehicle types, especially those with electronically controlled automatic transmissions. These examples are not exhaustive, but reflect real-world trends:

• Nissan (Altima, Maxima, Pathfinder, X-Trail)
• Ford (Focus, Fusion, Escape with automatic transmission)
• Mazda (Mazda6, CX-5, Mazda3)
• Infiniti (G35, Q50, QX60)
• Renault (certain models sharing Nissan platforms)

Common Mistakes & Best Practices for C1138 #

Misdiagnosis is common with this code. Many technicians and DIYers replace the sensor without checking the wiring, or overlook aftermarket electronics splicing into the circuit. To avoid wasted time and money, always follow a structured approach.

• Don’t replace the gear select sensor before thoroughly inspecting wiring and connectors.
• Never ignore signs of water intrusion around the transmission harness.
• Avoid guessing—use the correct wiring diagram for your vehicle’s year, make, and model.
• Always clear codes and confirm the repair with a test drive.
• Consult OEM service bulletins; some models have known harness issues or improved parts.

Quick FAQ about C1138 #

Q: Can a weak battery or alternator cause C1138?
A: Unlikely. This code refers specifically to an electrical short in the gear select circuit, not to general low power conditions.

Q: Will replacing the transmission fix this code?
A: No. C1138 almost always relates to wiring, connectors, or the gear select sensor itself, not the internal transmission hardware.

Q: Do I need a scan tool to clear the code after repairs?
A: Yes, use a scan tool to clear DTCs and confirm that C1138 does not return after a test drive.