Comprehensive diagnostic guide for OBD-II code P0708

What This Code Means

• Code: P0708
• Likely definition (manufacturer-agnostic): Transmission Range Sensor Circuit High Input
  • This definition aligns with the Open Source code entry described as (high signal from the position sensor for the lever), which corresponds to the transmission range/PRNDL sensor circuit reporting a high input to the powertrain control module (PCM/TCM).
  • Source note: Open Source GitHub definition indicates a high input from the transmission range/lever position sensor. See:
• Context in OBD-II: P0708 is one of the powertrain codes that the OBD-II system uses to indicate an issue with the transmission control system, specifically relating to the transmission range/gear selector position signal.
  • Source notes: OBD-II Diagnostic Trouble Codes and Powertrain Codes coverage describe how modern vehicles monitor transmission controls and generate codes when faults are detected. See Diagnostic Trouble Codes and Powertrain Codes for general framework.

Symptoms and real-user complaint patterns (typical behaviors you may observe)

• Transmission behavior
  • Erratic or delayed shifting, or no shifting from a given gear
  • Vehicle may enter a limp/fail-safe mode to protect the transmission
  • Gear selector display or dash indicator inconsistent with actual gear
  • In some cases, inability to shift out of Park/Drive or failure to shift through all gears
• MIL illumination
  • Check Engine Light (or MIL) may be on
• Related drivability concerns
  • Odd transmission feel, jolts during shifts
  • Possible speedometer or governor inconsistencies in some vehicles (since the transmission range data is used for gear logic)
    Note: These symptom patterns reflect common expectations when the PCM/TCM sees an abnormally high input on the transmission range sensor circuit. Individual vehicle behavior can vary by make/model.

Probable Causes

Because don't include a VIN-specific defect tree or NHTSA complaint frequencies for P0708, the probabilities below are grounded in typical ASE-field experience and general code behavior. They are given as approximate guidance rather than exact statistics.

• Most common cause: Faulty or misadjusted Transmission Range Sensor (TRS) or its mounting/adjustment
  • 35-50%
• Wiring harness, connectors, or harness damage between TRS and PCM/TCM (loose pins, corrosion, shorts to power or ground)
  • 20-30%
• Short to voltage or grounding issue on the TRS circuit at the PCM/TCM connector, or a faulty 5V reference/ground integrity
  • 10-15%
• PCM/TCM fault or software issue (less common, especially if the rest of the transmission control signals are otherwise functioning)
  • 5-15%
• Mechanical/valve-body issue within the transmission causing incorrect sensor signaling (less frequent for this specific code, but possible in some designs)
  • 5-10%
• Miscellaneous (intermittent wiring, sensor alignment drift, after-market wiring/adapters)
  • remainder

Step-by-Step Diagnosis

1) Confirm and scope the problem

• Use an OBD-II scan tool to confirm P0708 is present and note any related codes (P0700, P0701, P0702, P0705, etc.) that may indicate broader transmission-range control issues.
• Review freeze frame data and any live data related to the transmission range sensor/gain signals, and note the reported gear vs. actual vehicle status if available.
• Check for manufacturer-specific service information regarding the TRS circuit (some vehicles have shared grounds, 5V reference, or unique connector configurations).

2) Visual inspection and basic connectivity

• Inspect the TRS connector and the wiring harness for:
  • Damaged insulation, chafing, pin corrosion, bent pins, or loose fits at the PCM/TCM connector.
  • Signs of previous repairs or aftermarket wiring that might interfere with the TRS signal.
• Check for obvious mechanical misalignment or mounting issues of the transmission range sensor (TRS) relative to the gear selector linkage.
• Verify the gear selector linkage positions the TRS correctly; misalignment can cause out-of-range signals.

3) Electrical tests on the TRS circuit

• With ignition ON (engine OFF) and key in run:
  • Inspect the TRS circuit continuity between the TRS harness connector and the PCM/TCM harness connector.
  • Check for shorts to voltage or ground on the TRS signal line.
  • Measure reference voltage and ground integrity on the PCM/TCM side of the TRS circuit. Some systems use a 5V reference; verify that reference is present and stable.
• Use a multimeter (and if possible, an oscilloscope) to observe the TRS signal while moving the gear selector through PRNDS (Park, Reverse, Neutral, Drive, Sport, etc., depending on the vehicle). The signal should change with position; a consistently high input or stuck high reading indicates a TRS or wiring fault.

4) Sensor and harness-specific checks

• TRS sensor condition:
  • If the sensor is suspect (out of spec or mechanical wear), replace it per the service manual. Some vehicles require sensor alignment/calibration after replacement.
• Connector pins:
  • Clean any corrosion with appropriate contact cleaner; reseat connectors firmly; ensure proper pin seating and lock mechanism engagement.
• Wiring harness integrity:
  • Look for cracked insulation, exposed wires, or areas where movement could cause intermittent shorts or opens.

5) Validate against other related codes and data

• If P0708 is accompanied by P0700 or P0705 (range sensor/malfunction-related codes), that can reinforce suspicion of sensor or wiring issues rather than a PCM fault alone.
• After repairs, clear codes and perform a road test or drive cycle while monitoring live data to verify the TRS signal tracks gear selection correctly and the code does not reoccur.

6) Repair steps (action-oriented)

• If TRS is defective:
  • Replace TRS and, if required, recalibrate/alignment per the service procedure.
• If wiring/wiring harness issues are found:
  • Repair damaged wires, replace faulty harness sections, re-pin connectors as needed, and ensure proper routing to prevent future chafing.
• If connectors are corroded or pins are damaged:
  • Clean or replace connectors; reseat with dielectric grease if appropriate; ensure secure fit.
• After hardware repair:
  • Clear codes, perform a controlled test drive to verify transmission behavior, and recheck live data to ensure the TRS signal now corresponds correctly to gear selection.
• If the problem persists after TRS and wiring repair:
  • Consider PCM/TCM software update or, in rare cases, PCM/TCM replacement after re-evaluating all connections and sensor signals.
• Note on calibration:
  • Some vehicles require a TRS alignment or relearn procedure after TRS replacement or after certain electrical repairs. Follow the manufacturer service procedure for relearn/calibration.

Safety Considerations

• Always work on a vehicle with it secured and the parking brake applied; use wheel chocks during tests.
• If you disconnect the battery or work near air-bag modules or other high-voltage components, follow proper safety procedures and allow capacitors to discharge as required.
• Be cautious around hot exhaust and moving parts when the engine is running during testing.

What to document and report

• Document all findings: sensor readings, wiring resistance/continuity results, connector condition, and any misalignment observed.

• Record the exact symptoms observed during the drive cycle and the corresponding TRS data readings from the scan tool.

• Note any service manual steps performed (alignment/relearn procedures) and the results after repairs.

• General framework and code concept:

  • OBD-II and Diagnostic Trouble Codes overview - Diagnostic Trouble Codes; Powertrain Codes; Emissions Testing. These sections describe how modern vehicles use diagnostic trouble codes in powertrain control systems and the role of OBD-II in emissions and driveability diagnostics.

• Code definition alignment:

  • Open Source code definition , which corresponds to a transmission range/gear selector circuit high input. This supports the interpretation that P0708 relates to a high input on the transmission range sensor circuit.

• Practical context for troubleshooting:

  • The OBD-II sections on Diagnostic Trouble Codes and Powertrain Codes provide the framework for how P0708 fits into overall powertrain diagnostics, including the need to verify sensor signals, wiring, and control-module behavior during troubleshooting.

• If a conflict arises between general code guidance and vehicle-specific service information, rely on the vehicle-specific service manual for TRS wiring, signal ranges, pinouts, and relearn procedures, and treat the general guidance as supporting context.

Summary

• P0708 points to a high signal on the transmission range sensor circuit, implicating the TRS itself, its wiring, or related PCM/TCM interpretation. The most common root cause is a faulty/misaligned TRS or compromised wiring/connectors, followed by electrical faults in the circuit, PCM/TCM issues, or less commonly mechanical/transmission concerns. A systematic diagnostic approach-starting with a visual/wiring inspection, followed by electrical tests of the TRS circuit, sensor replacement if needed, and finally calibration/relearn as required by the vehicle-will reliably identify and correct the issue. Always clear codes after repair and verify with a test drive and live data monitoring to ensure the fault is resolved.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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