The 0708 Generic Obd2 Code, also known as the P0708 code, signals a “Transmission Range Sensor ‘A’ Circuit High” issue within your vehicle’s powertrain system. This code is a standardized diagnostic trouble code (DTC), meaning it’s applicable across vehicles equipped with OBD-II systems. While the code is generic, specific repair steps can differ depending on the car’s make and model.
This particular DTC falls under the “B” type category within the transmission subgroup. This classification means that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) requires detecting the fault condition in two consecutive drive cycles (key on-off, then on-off again) before activating the check engine light.
The PCM or TCM relies on the transmission range sensor, sometimes referred to as the inhibitor switch, to accurately determine the position of the gear shift lever. The P0708 code is triggered when the system receives conflicting signals, indicating two different gear positions simultaneously for a duration exceeding 30 seconds. If this malfunction occurs in two subsequent drive cycles, the check engine light will illuminate, and the transmission might enter a “fail-safe” or “limp-home” mode to prevent further damage.
Example of an external Transmission Range Sensor (TRS):
Decoding the P0708 Code: Meaning and Function
The core issue behind the P0708 code lies within the transmission range sensor circuit. This sensor plays a crucial role in informing your vehicle’s computer (PCM/TCM) about the selected gear. Think of it as the communication bridge between your gear selector and the transmission’s electronic control system.
The “A Circuit High” designation specifically points to an abnormally high voltage reading within the sensor’s circuit. This “high” reading doesn’t necessarily mean excessive voltage in an absolute sense, but rather that the voltage signal is outside the expected operating range for proper sensor function. The computer interprets this unusual signal as a malfunction within the transmission range sensor system.
Symptoms Associated with the 0708 Code
When the P0708 code is active, you’ll likely notice several symptoms affecting your vehicle’s performance:
- Check Engine Light Illumination: This is the most immediate and obvious sign. The malfunction indicator lamp on your dashboard will light up to alert you to a problem.
- Reduced Power and “Limp Mode”: A common consequence is a noticeable decrease in engine power, especially when starting from a standstill. This occurs because the transmission might default to starting in a higher gear, like third gear, as a safety measure. This “limp-home” mode is designed to protect the transmission from further damage.
- Transmission Performance Issues: You might experience erratic shifting, delayed gear changes, or an inability to shift into certain gears. The transmission’s overall behavior may become unpredictable.
Ignoring these symptoms and continuing to drive with the P0708 code can lead to significant and costly transmission damage. Prompt diagnosis and repair are crucial to prevent escalating problems.
Potential Causes of the P0708 Trouble Code
Several factors can contribute to the P0708 code. Pinpointing the exact cause requires a systematic diagnostic approach. Here are the common culprits:
- Faulty Transmission Range Sensor (TRS): The sensor itself might be malfunctioning due to internal wear, electrical failure, or damage. This is often the most frequent cause.
- Misadjusted Transmission Shift Cable or Linkage: If the mechanical linkage connecting the gear shifter to the transmission is improperly adjusted, it can lead to incorrect sensor readings and trigger the P0708 code.
- Wiring Problems: Damaged, corroded, or shorted wiring within the transmission range sensor circuit can disrupt the electrical signals and cause a “Circuit High” condition. This includes issues with connectors and harnesses.
- Misadjusted Range Sensor: Even if the sensor isn’t faulty, improper installation or adjustment can lead to incorrect readings and the activation of the P0708 code.
- PCM or TCM Failure (Rare): While less common, a fault within the PCM or TCM itself can, in rare instances, cause the P0708 code. However, it’s essential to rule out other possibilities first, as PCM/TCM failures are less frequent in range sensor related issues.
Diagnosing and Repairing the P0708 Code: A Step-by-Step Guide
Diagnosing the P0708 code effectively involves a combination of visual inspection and electrical testing. Here’s a breakdown of the diagnostic process:
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Initial Scan with an OBD-II Scanner: Use an OBD-II scanner to confirm the presence of the P0708 code and check for any other related trouble codes. This provides a starting point for diagnosis.
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Visual Inspection:
- Inspect Wiring and Connectors: Carefully examine the wiring and connectors associated with the transmission range sensor. Look for signs of damage, fraying, corrosion, or loose connections.
- Check Shift Linkage: Assess the transmission shift cable and linkage for proper adjustment and smooth operation. Ensure there’s no binding or excessive play.
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Electrical Testing (Using a Multimeter):
- Voltage Check: With the ignition key in the “ON” position and the engine off (KOEO), use a digital voltmeter to check the voltage at the transmission range sensor connector. You’ll need to refer to your vehicle’s wiring diagram for specific pin assignments.
- Signal Circuit Testing: Back-probe the sensor’s signal circuits while it’s still connected. Have an assistant shift through each gear position one at a time. Each signal circuit should show voltage in only one gear position. If voltage is present in multiple gear positions on a single circuit, it indicates a likely sensor malfunction.
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Sensor Replacement (If Necessary): If the diagnostic tests point to a faulty transmission range sensor, replacement is usually required. Ensure you use a high-quality replacement sensor that’s compatible with your vehicle.
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Shift Linkage Adjustment (If Necessary): If misadjusted shift linkage is suspected, follow your vehicle’s service manual to perform the correct adjustment procedure.
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Wiring Repair (If Necessary): Repair any damaged wiring, connectors, or harnesses identified during the visual inspection or electrical testing.
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Code Clearing and Retest: After completing repairs, clear the P0708 code using the OBD-II scanner. Then, perform a test drive to see if the code returns. Monitor the system to ensure the issue is resolved.
Important Note: While PCM/TCM failure is a rare cause, consider it as a last resort after thoroughly investigating other potential causes. If you suspect a PCM/TCM issue, carefully check for any signs of damage, especially if there’s a history of shorts in the range sensor circuit. Always address the root cause of any damage before replacing the PCM/TCM to prevent recurrence.
Severity and Urgency of Addressing P0708
The P0708 code should be addressed promptly. Continuing to drive with this code active can lead to:
- Transmission Damage: Operating in “limp mode” or with incorrect gear selection can place undue stress on transmission components, leading to premature wear and potentially severe internal damage.
- Safety Concerns: Unpredictable transmission behavior can create unsafe driving conditions, especially in situations requiring quick acceleration or gear changes.
- Increased Repair Costs: Delaying repairs can allow minor issues to escalate into major transmission problems, resulting in significantly higher repair bills.
It’s highly recommended to have your vehicle diagnosed and repaired as soon as possible after the P0708 code appears to prevent further complications and ensure safe and reliable vehicle operation.
Related OBD-II Codes to P0708
Several other OBD-II codes are related to the transmission range sensor system. These codes can sometimes appear alongside or instead of P0708, depending on the specific nature of the problem:
- P0705: Transmission Range Sensor Circuit Malfunction
- P0706: Transmission Range Sensor Circuit Range/Performance
- P0707: Transmission Range Sensor “A” Circuit Low
- P0709: Transmission Range Sensor Circuit Intermittent
Understanding these related codes can provide a more comprehensive view of potential issues within the transmission range sensor system.
Need Further Assistance with P0708?
If you require more in-depth troubleshooting guidance or have specific questions about the P0708 trouble code in your vehicle, we encourage you to consult a certified automotive technician or utilize online resources, such as car repair forums, for community-based support and advice.
Disclaimer: This information is intended for informational purposes only and should not be considered as professional repair advice. We are not liable for any actions taken on your vehicle based on this information. Always consult with a qualified technician for diagnosis and repair procedures.
