Transmission Range Sensor Circuit High
The P0708 code indicates that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected an abnormally high voltage signal from the Transmission Range Sensor (TRS) circuit. This means the sensor's output voltage exceeds the maximum calibrated threshold for the current gear position, indicating a circuit fault or internal sensor failure.
This code is considered high severity because the vehicle's computer cannot accurately determine which gear is selected. This can lead to a no-start condition (due to the neutral safety switch function) or erratic, unsafe shifting while driving.
Common symptoms
- Check Engine Light illuminated
- Vehicle will not crank or start
- Harsh or erratic transmission shifting
- Transmission stuck in Limp Mode (default gear)
- Incorrect or blank gear indicator on the dashboard
Likely causes
- Defective Transmission Range Sensor (TRS) / Neutral Safety Switch
- Corroded, damaged, or loose wiring connector at the TRS
- Short to voltage in the TRS wiring harness
- Misadjusted Transmission Range Sensor or shift linkage
- Failed Powertrain Control Module (PCM) or Transmission Control Module (TCM)
What to check before replacing parts
Scan for codes and verify the gear indicator on the dash matches the physical shifter position.
Look for: If the dash indicator is blank, flashes, or shows the wrong gear, the sensor or its alignment is faulty.
Visually inspect the Transmission Range Sensor and its electrical connector.
Look for: Look for corrosion, water intrusion, bent pins, or damaged wires that could cause a short to voltage.
Check the adjustment of the shift cable and the Transmission Range Sensor.
Look for: Verify that the linkage moves the sensor to the correct detents without binding or misalignment.
Test the TRS circuit for a short to voltage using a digital multimeter.
Look for: Disconnect the sensor and check the signal wire for voltage; if voltage is present when it shouldn't be, there is a short in the harness.
Test the Transmission Range Sensor internal resistance or voltage output according to service manual specifications.
Look for: If the sensor outputs a voltage higher than the specified range (usually above 4.8V) for any gear position, the sensor itself has failed internally.
This page explains the generic P0708 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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