P0708 Code: Here's How to Solve It Fast

The P0708 trouble code is a diagnostic trouble code (DTC) that indicates an issue with the Transmission Range Sensor Circuit High Input. This code is triggered when the Engine Control Module (ECM) detects that the voltage from the transmission range sensor is higher than expected, suggesting a malfunction in the sensor or its circuit. The transmission range sensor, often referred to as the PRNDL switch, plays a crucial role in informing the vehicle’s computer about the current gear position, which is essential for proper transmission operation.

Understanding this code is vital for vehicle owners and DIY mechanics, as it can lead to significant drivability issues if not addressed promptly. Below is a comprehensive overview of the P0708 code, including its meaning, common causes, symptoms, diagnosis steps, and solutions.

P0708 Code Meaning	P0708 Code Common Causes
Transmission Range Sensor Circuit High Input	Misadjusted transmission range sensor
Indicates high voltage input from the sensor	Faulty transmission range sensor
Potential issues with the transmission control module (TCM)	Damaged or corroded wiring connections
May cause improper shifting behavior	Faulty Engine Control Module (ECM)

Symptoms of P0708 Code

When the P0708 code is present, drivers may notice several symptoms that can impact vehicle performance:

• Check Engine Light: The most obvious indication is the illumination of the check engine light on the dashboard.
• Transmission Issues: Drivers may experience hard shifting or difficulty in changing gears. The vehicle might unexpectedly shift to neutral or fail to engage certain gears.
• Decreased Fuel Economy: Abnormal shifting patterns can lead to inefficient fuel consumption.
• Performance Problems: The vehicle may exhibit sluggish acceleration or reduced power.
• Fail-Safe Mode Activation: In some cases, vehicles may enter a fail-safe mode to prevent further damage, limiting engine power and speed.

Technical Explanation of P0708

The P0708 code signifies that there is an issue with the transmission range sensor, which communicates the position of the gear selector to the ECM. This sensor sends voltage signals corresponding to its position (Park, Reverse, Neutral, Drive). When these signals are outside expected parameters—specifically when they indicate a high voltage—the ECM triggers the P0708 code.

Step-by-Step Diagnosis

To effectively diagnose a P0708 code, follow these steps:

1. Scan for Codes: Use an OBD-II scanner to confirm that P0708 is present and check for any related codes that might provide additional context.
2. Inspect Wiring and Connectors: Examine all wiring and connectors associated with the transmission range sensor for signs of damage, corrosion, or disconnection.
3. Check Sensor Adjustment: Consult the vehicle’s service manual for specific instructions on adjusting the transmission range sensor. Misalignment can lead to incorrect readings.
4. Test Sensor Operation: Using a multimeter, measure the voltage output from the transmission range sensor while moving through each gear position. Compare these readings against manufacturer specifications.
5. Inspect ECM Functionality: If all other components are functioning correctly but the code persists, consider testing or replacing the ECM.

Solution Methods for P0708 Code

Adjusting Transmission Range Sensor

Symptoms

• Misalignment causing incorrect voltage readings.

Technical Explanation

The transmission range sensor must be calibrated correctly to ensure accurate signal transmission to the ECM.

Step-by-Step Solution

1. Locate the transmission range sensor according to your vehicle's service manual.
2. Loosen any mounting bolts or screws.
3. Adjust the sensor position as per manufacturer specifications.
4. Tighten all fasteners and recheck for codes.

Cost Estimates

• Adjustment labor costs typically range from $50 to $100 depending on local rates.

Warnings and Recommendations

Ensure that adjustments are made following manufacturer guidelines to avoid further issues.

Replacing Faulty Transmission Range Sensor

Symptoms

• Persistent P0708 code after adjustment attempts.

Technical Explanation

A faulty sensor will continuously send incorrect signals leading to erratic shifting behavior.

Step-by-Step Solution

1. Disconnect battery power.
2. Remove any components obstructing access to the transmission range sensor.
3. Disconnect wiring harness from the old sensor.
4. Install a new sensor and reconnect wiring.
5. Reassemble components and reconnect battery power.
6. Clear codes and test drive to ensure proper function.

Cost Estimates

• Replacement parts typically cost between $50 and $150; labor can add another $100 to $200.

Warnings and Recommendations

Always disconnect battery power before working on electrical components to prevent shorts or shocks.

Repairing Damaged Wiring

Symptoms

• Visual signs of wear or corrosion on wiring harnesses.

Technical Explanation

Damaged wiring can interrupt signal flow between components, leading to erroneous readings.

Step-by-Step Solution

1. Inspect all wiring connected to the transmission range sensor.
2. Repair any frayed or damaged wires using solder and heat shrink tubing.
3. Replace any corroded connectors with new ones.
4. Secure all wiring away from moving parts or heat sources.

Cost Estimates

• Repair costs vary widely; expect anywhere from $20 for simple repairs up to $200 for extensive rewiring.

Warnings and Recommendations

Ensure repairs are insulated properly to prevent future shorts or exposure.

Replacing ECM (if necessary)

Symptoms

• All other parts tested good but code persists.

Technical Explanation

A malfunctioning ECM may misinterpret signals from various sensors due to internal faults.

Step-by-Step Solution

1. Verify that all other components are functioning correctly before considering ECM replacement.
2. Disconnect battery power.
3. Remove old ECM following manufacturer guidelines.
4. Install new ECM and ensure it is programmed correctly for your vehicle model.
5. Reconnect battery power and clear codes.

Cost Estimates

• A new ECM can cost between $200 and $800; programming fees may add another $100-$200 depending on dealership rates.

Warnings and Recommendations

Professional installation is recommended due to complexities involved in programming new units.

Closing Paragraph

The P0708 trouble code indicates a significant issue with your vehicle's transmission range sensor circuit that should not be ignored. Addressing this problem promptly can prevent further damage and ensure optimal performance of your vehicle's transmission system. Whether you choose to tackle this issue yourself or seek professional assistance, understanding each step in diagnosing and fixing this code will empower you as a vehicle owner or DIY mechanic.

Frequently Asked Questions About P0708

• What does error code P0708 mean?
  P0708 indicates a high input signal from the Transmission Range Sensor Circuit.
• Can I drive my car with a P0708 code?
  While it may be drivable, doing so can lead to severe transmission damage over time.
• How much does it cost to fix a P0708 code?
  The cost can vary widely but typically ranges from $50 for adjustments up to $800 for ECM replacement.
• Is it safe to drive with a P0708 code?
  No, driving with this code can result in erratic shifting behavior and potential damage.
• What are common symptoms of a P0708 code?
  Common symptoms include hard shifting, decreased fuel economy, and illuminated check engine light.
• How do I reset a P0708 code?
  You can reset it by clearing codes with an OBD-II scanner after repairs are made.
• Should I replace my transmission range sensor immediately?
  If diagnostics confirm it's faulty after adjustments, replacement is necessary.
• Can I adjust my own transmission range sensor?
  Yes, if you follow your vehicle's service manual instructions carefully.