As an auto repair expert at autelfrance.com, I’m here to break down the OBDII P0708 trouble code. This article will provide a comprehensive understanding of this code, its symptoms, causes, and how to diagnose and potentially fix it. We’ll focus on providing clear, actionable information to help you understand and address this issue.
Decoding the P0708 Trouble Code
The P0708 code is a generic powertrain code, meaning it can occur in any vehicle equipped with an OBD-II system. Specifically, it’s defined as Transmission Range Sensor “A” Circuit High. This indicates a problem within the transmission control system, specifically with the Transmission Range Sensor (TRS), sometimes also referred to as the inhibitor switch or Neutral Safety Switch.
Image: An example of an external Transmission Range Sensor, crucial for identifying gear position and preventing vehicle start in drive. This sensor is often the culprit behind a P0708 code.
This code is considered a type “B” DTC. This designation means that the vehicle’s Powertrain Control Module (PCM) or Transmission Control Module (TCM) requires the fault condition to be detected across two consecutive drive cycles (key on-off, off-on) before illuminating the check engine light. This built-in verification helps prevent false alarms and ensures a genuine issue is present.
When the PCM or TCM detects conflicting signals from the Transmission Range Sensor, indicating two or more gear positions simultaneously for an extended period (typically over 30 seconds), the P0708 code is triggered. If this occurs in two consecutive drive cycles, the check engine light will activate, and the transmission may enter a “fail-safe” or “limp-home” mode to protect itself from further damage.
Recognizing the Symptoms of a P0708 Code
When the P0708 code appears, you’ll likely notice several symptoms affecting your vehicle’s performance. The most common and noticeable symptoms include:
- Check Engine Light Illumination: This is the primary indicator that something is wrong with your vehicle’s system.
- Reduced Engine Power: The most prominent drivability issue is often a significant lack of power, particularly when starting from a complete stop. This occurs because the transmission may default to starting in a higher gear, typically third gear, instead of first.
- Transmission Limp Mode: To protect itself, the transmission may enter a limp-home mode, limiting gear selection and overall performance. This is a safety measure to prevent further damage.
- Difficulty Shifting Gears: You might experience unusual shifting patterns, harsh shifts, or an inability to shift into certain gears.
- Possible No-Start Condition: In some cases, a faulty TRS can prevent the engine from starting, as the system may not correctly recognize the vehicle is in “Park” or “Neutral”.
Severity of the P0708 Code:
Ignoring the P0708 code can lead to more serious and expensive transmission problems. Continued driving with this issue can cause internal transmission damage due to improper gear engagement and increased stress. It is highly recommended to address this problem promptly to avoid costly repairs down the line.
Pinpointing the Causes of P0708
Several factors can contribute to the P0708 code. Accurately diagnosing the root cause is crucial for effective repair. Potential causes include:
- Faulty Transmission Range Sensor (TRS): This is the most common culprit. The sensor itself may be malfunctioning internally, sending incorrect or erratic signals to the PCM/TCM.
- Misadjusted Transmission Shift Cable or Linkage: If the mechanical linkage connecting the gear shifter to the transmission is improperly adjusted, it can cause the TRS to misread the selected gear position.
- Damaged Wiring or Connectors: Wiring issues such as shorts, opens, corrosion, or damage to the wiring harness or connectors associated with the TRS circuit can disrupt signal transmission and trigger the code.
- Misadjusted Range Sensor: Even if the sensor is not faulty, improper installation or adjustment of the TRS can lead to incorrect readings and the P0708 code.
- (Rarely) PCM or TCM Failure: While less frequent, a malfunctioning PCM or TCM could misinterpret signals from a functioning TRS or have internal issues affecting the range sensor circuit.
Diagnostic Steps for P0708
Diagnosing the P0708 code requires a systematic approach to pinpoint the source of the problem. Here’s a step-by-step diagnostic procedure:
- Initial Scan: Use an OBD-II scan tool to confirm the presence of the P0708 code and check for any other related trouble codes. Note down all codes present.
- Visual Inspection: Carefully inspect the Transmission Range Sensor, its wiring harness, and connectors for any signs of physical damage, corrosion, or loose connections. Pay close attention to the wiring near the sensor and along its routing path.
- Shift Linkage Inspection: Examine the transmission shift cable and linkage for proper adjustment and any signs of damage, binding, or wear. Ensure the linkage moves freely and corresponds correctly with the gear selector positions.
- Sensor Circuit Testing (Using a Multimeter):
- With the ignition key in the “ON” position and the engine OFF (KOEO), use a digital multimeter to check the voltage at the TRS connector.
- Identify the 12-volt power supply wire to the sensor. Verify proper voltage is reaching the sensor.
- Back-probe each signal wire from the TRS while an assistant slowly shifts through each gear position (P, R, N, D, etc.).
- Each signal circuit should show voltage in only one gear position and no voltage in other positions. If voltage is present in multiple gear positions on a single circuit, it strongly indicates a faulty TRS.
- Scan Tool Data Monitoring (Advanced): If you have an advanced scan tool capable of reading live data, monitor the Transmission Range Sensor data while shifting gears. Observe if the sensor readings are consistent with the selected gear position and if there are any erratic or illogical fluctuations.
Important Note on PCM/TCM Failure:
While PCM or TCM failure is a less common cause of P0708, it’s essential to consider it, especially after ruling out other possibilities. In my experience, PCM/TCM issues related to range sensor codes are rare, but they can occur. If you suspect a PCM/TCM fault, thoroughly investigate for any potential short circuits in the TRS or its wiring that might have caused damage to the module before replacing it. Replacing a damaged PCM/TCM without addressing the underlying short can lead to repeat failures.
Repairing the P0708 Code
The repair procedure for a P0708 code depends on the diagnosis. Common repairs include:
- Transmission Range Sensor Replacement: If the sensor is identified as faulty through testing, replacement is necessary. Ensure you use a high-quality replacement sensor and properly adjust it according to the manufacturer’s specifications.
- Shift Linkage Adjustment: If the shift linkage is misadjusted, carefully adjust it to ensure proper gear selection and accurate TRS readings. Refer to the vehicle’s service manual for specific adjustment procedures.
- Wiring Repair: Repair any damaged wiring or connectors in the TRS circuit. This may involve splicing wires, replacing connectors, or repairing shorts to ground or power.
- PCM/TCM Replacement (Rare): Only replace the PCM or TCM if all other potential causes have been ruled out and you have confirmed a module fault.
After completing any repairs, clear the P0708 code using a scan tool and perform a test drive to ensure the code does not return and the vehicle is operating correctly.
Related OBDII Codes
Understanding related codes can provide a broader context when diagnosing transmission issues. Codes often related to P0708 and the Transmission Range Sensor include:
- P0705: Transmission Range Sensor Circuit Malfunction
- P0706: Transmission Range Sensor Circuit Range/Performance
- P0707: Transmission Range Sensor “A” Circuit Low
- P0709: Transmission Range Sensor “A” Circuit Intermittent
Need Further Assistance?
If you’re still struggling with the P0708 code after reviewing this guide, don’t hesitate to seek further assistance. For personalized troubleshooting and advice, consider posting your specific question in our FREE car repair forums. Our community of experienced technicians and enthusiasts can offer valuable insights and guidance to help you resolve your P0708 issue.
Disclaimer: This information is for informational purposes only and should not be considered professional repair advice. We are not responsible for any actions taken based on this information. Always consult a qualified automotive technician for diagnosis and repair.
