C1135

What Does Code C1135 Mean?

The diagnostic trouble code C1135 indicates a detected electrical malfunction within the circuit of the Gear Shift Position (GSP) sensor, specifically a “short to battery” condition. This fault is monitored by the Powertrain Control Module (PCM), or in some applications, the Transmission Control Module (TCM). The GSP sensor, often integrated into a Transmission Range Sensor (TRS) or a Park/Neutral Position (PNP) switch, is a critical input device that communicates the driver’s selected gear (e.g., Park, Reverse, Neutral, Drive, Low) to the control module. The module relies on a precise voltage signal or resistance value from this sensor to accurately determine the transmission’s state. A “short to battery” means that the signal circuit for the GSP sensor is receiving an abnormally high voltage, typically at or near the vehicle’s battery voltage (approximately 12V), which is well outside the expected operating range for the sensor’s signal output (which might be 0-5V, or specific stepped voltages for each gear). This prevents the control module from obtaining a valid gear position input, leading to confusion regarding the transmission’s actual state and potentially impacting vehicle drivability, starting, and safety features.

Common Symptoms

• Vehicle will not start or crank, especially if the module cannot confirm “Park” or “Neutral.”
• Transmission shifting erratic or operating in a default “limp mode,” resulting in harsh shifts or being stuck in a single gear.
• Reverse lights do not illuminate or remain on regardless of gear selection.
• PRNDL display on the instrument cluster is inaccurate, intermittent, or completely blank.
• Vehicle may start in gears other than Park or Neutral (a significant safety concern).
• Cruise control may be inoperative.

What Causes the Code C1135?

• Short circuit to battery voltage in the Gear Shift Position sensor signal wire or its associated harness. This is the most direct and common cause.
• Damaged or chafed wiring harness where the GSP sensor wiring comes into contact with a power wire or a vehicle component providing battery voltage.
• Internal fault within the Gear Shift Position sensor itself, causing a permanent internal short to its own power supply or a short within the sensor’s output circuit.
• Corrosion or moisture ingress within the GSP sensor connector or the harness connector, leading to shorting between pins.
• Less commonly, an internal fault within the PCM/TCM that incorrectly applies battery voltage to the GSP sensor signal input, although this typically accompanies other module-related codes.

How to Diagnose and Troubleshoot

Diagnosing C1135 requires careful electrical testing and visual inspection. Always begin with a thorough visual inspection of the GSP sensor and its associated wiring harness.

1. Visual Inspection:
   • Inspect the GSP sensor and its electrical connector for signs of damage, corrosion, or contamination.
   • Carefully trace the wiring harness from the GSP sensor back to the control module. Look for signs of chafing, rubbing, melting, or rodent damage, particularly where the harness passes through sharp edges, around moving parts, or near exhaust components.
   • Ensure all connectors are fully seated and free from bent or pushed-out pins.
2. Scan Tool Data Analysis:
   • Connect an OBD-II scan tool and access live data for the Transmission Range Sensor (TRS) or Gear Shift Position (GSP) input.
   • With the ignition ON and engine OFF, observe the reported gear position and its corresponding voltage or resistance value. If C1135 is present, the scan tool will likely report an erroneous gear position or a voltage value consistently near battery voltage (e.g., 10-14V), regardless of the actual shifter position.
3. Digital Multimeter (DMM) Testing at the Sensor Connector:
   • With the ignition OFF, disconnect the GSP sensor electrical connector.
   • Check for short to battery on the signal wire: Turn the ignition ON. Using a DMM, back-probe the signal wire terminal (refer to OEM wiring diagrams for pinout) at the harness side of the disconnected connector. Measure the voltage between this terminal and a known good ground. If you measure battery voltage (e.g., 12V) on the signal wire, it confirms a short to battery voltage within the wiring harness leading to the control module.
   • Check for continuity to B+: With the ignition OFF, measure resistance between the GSP signal wire terminal at the harness connector and the B+ terminal (or any constant 12V source in the vehicle, with power disconnected from that source if possible). There should be infinite resistance (open circuit). Any measurable resistance indicates a short.
   • Check sensor integrity (if applicable): If the sensor is a simple switch or provides stepped resistance, test its output while manually moving the shifter through all positions. For resistance-type sensors, measure resistance across the appropriate sensor terminals. For voltage-output sensors (if it’s an active sensor), reconnect it temporarily, back-probe the signal wire, and observe voltage changes as the shifter is moved (expected to be within a specific range, usually 0-5V, not battery voltage).
4. Isolation Testing:
   • If a short to battery voltage is confirmed on the harness side, the next step is to isolate the short. You may need to disconnect the harness at intermediate points or even at the PCM/TCM connector.
   • Measure the resistance/voltage on the signal wire segment-by-segment to pinpoint where the short occurs.

Recommended Repairs and Solutions

Once the source of the short to battery is identified, the appropriate repair can be made:

• Repair or Replace Damaged Wiring Harness: If the short is found within the wiring harness, the damaged section must be repaired or the entire harness segment replaced. Ensure proper splicing techniques are used, with heat-shrink tubing and dielectric grease to prevent future issues. Reroute the harness to prevent reoccurrence of chafing or damage.
• Replace Faulty Gear Shift Position Sensor / Transmission Range Sensor: If testing confirms an internal short within the GSP sensor itself, the sensor must be replaced. After replacement, ensure proper adjustment if the sensor is mechanically adjustable (e.g., older style TRS).
• Clean and Repair Corroded Connectors: If corrosion was the culprit, clean the connector terminals thoroughly with electrical contact cleaner and a small brush. If pins are severely corroded or damaged, consider replacing the connector housing and pins. Apply dielectric grease to prevent future corrosion.
• Address PCM/TCM Internal Fault (Rare): In very rare cases, if all wiring and sensor testing confirms integrity, the fault may lie within the control module itself. This is typically a last resort diagnosis and requires specialized diagnostic equipment for verification and potentially module replacement and programming.
• After any repair, clear the C1135 diagnostic trouble code using a scan tool. Perform a road test to verify the repair and ensure the code does not return and that all transmission functions are operating correctly.