P0879 Code: Complete DIY Repair Guide

The P0879 trouble code is a diagnostic trouble code (DTC) that indicates an issue with the Transmission Fluid Pressure Sensor/Switch “D” Circuit. This code is part of the OBD-II system, which monitors various vehicle components to ensure optimal performance and safety. When the engine control module (ECM) detects that the transmission fluid pressure sensor is providing inconsistent or incorrect readings, it triggers the P0879 code. This can lead to various transmission issues, including poor shifting performance and potential damage to the transmission system if not addressed promptly.

Symptoms of P0879 Code

When dealing with a P0879 code, vehicle owners may notice several symptoms indicating a problem with the transmission system. Common symptoms include:

• Malfunction Indicator Light (MIL): The check engine light will typically illuminate.
• Poor Shifting Performance: The vehicle may experience rough or harsh shifting between gears.
• Limp Mode Activation: The vehicle may start in second or third gear to protect the transmission.
• Increased Fuel Consumption: Inefficient shifting can lead to higher fuel usage.
• Transmission Slipping: The transmission may slip out of gear unexpectedly.

Technical Explanation of P0879 Code

The P0879 code is primarily associated with the Transmission Fluid Pressure Sensor/Switch “D.” This sensor monitors the hydraulic pressure within the transmission and sends this information to the TCM. The TCM uses this data to adjust shifting patterns and ensure smooth operation. If the sensor fails or provides intermittent signals, it can lead to improper shifting and potential damage to the transmission.

Step-by-Step Diagnosis

Diagnosing a P0879 trouble code involves several steps:

1. Check for Other Codes: Use an OBD-II scanner to check for additional trouble codes that may provide more context about the issue.
2. Visual Inspection: Inspect the wiring and connectors associated with the Transmission Fluid Pressure Sensor for signs of damage, corrosion, or loose connections.
3. Transmission Fluid Level Check: Ensure that the transmission fluid is at the correct level as low fluid can affect pressure readings.
4. Test the Sensor: Disconnect the sensor and test its resistance using a multimeter according to manufacturer specifications.
5. Check Electrical Connections: Ensure that all electrical connections are secure and free from corrosion.
6. Clear Codes and Test Drive: After making any repairs, clear the codes and take the vehicle for a test drive to see if the P0879 code returns.

Solution Methods for P0879 Code

Addressing a P0879 trouble code can vary based on the underlying cause:

1. Replace Faulty Transmission Fluid Pressure Sensor

If diagnostics indicate that the sensor is faulty, replacing it is often necessary.

• Cost Estimate: The cost for a new sensor typically ranges from $50 to $150, depending on make and model.

2. Repair Wiring Issues

If damaged wiring or connectors are found during inspection, they must be repaired or replaced.

• Cost Estimate: Wiring repairs can vary widely but expect costs from $100 to $300 based on labor rates and extent of damage.

3. Refill Transmission Fluid

If low fluid levels are detected, topping off or replacing contaminated fluid may resolve the issue.

• Cost Estimate: A fluid change typically costs between $100 and $200 depending on labor and type of fluid used.

4. Replace Transmission Control Module (TCM)

In rare cases where other solutions do not resolve the issue, replacing the TCM might be necessary.

• Cost Estimate: A new TCM can cost between $200 and $600 plus programming fees.

Warnings and Recommendations

• Always consult your vehicle’s service manual for specific diagnostic procedures related to your make and model.
• If you are not confident in performing these diagnostics or repairs, seek professional assistance from a certified mechanic.
• Ignoring a P0879 code can lead to severe transmission damage, resulting in costly repairs down the line.

Closing Paragraph

The P0879 trouble code indicates an important issue within your vehicle’s transmission system that should not be ignored. Proper diagnosis and timely repairs can prevent further complications and ensure your vehicle operates smoothly. By following this guide, DIY mechanics can effectively troubleshoot and resolve issues related to this error code while maintaining their vehicle’s performance and reliability.

Frequently Asked Questions About P0879

• What does error code P0879 mean?
  P0879 indicates an intermittent issue with the Transmission Fluid Pressure Sensor/Switch “D” Circuit.
• What are common symptoms of P0879?
  Common symptoms include poor shifting performance, increased fuel consumption, and activation of limp mode.
• Can I drive my car with a P0879 code?
  While it may be possible, it’s not recommended as it could lead to further damage to your transmission.
• How do I diagnose a P0879 code?
  The diagnosis involves checking for other codes, inspecting wiring, testing the sensor, and ensuring proper fluid levels.
• What should I do if I see a P0879 code?
  You should perform diagnostics as outlined in this guide or consult a professional mechanic.
• Is replacing the Transmission Fluid Pressure Sensor difficult?
  This task can vary in difficulty based on vehicle make; consult your service manual for guidance.
• Will clearing codes fix my car?
  No, clearing codes will not fix underlying issues; it only resets the check engine light.
• How much does it cost to fix a P0879 code?
  The cost varies widely based on repairs needed but typically ranges from $50 for a sensor replacement up to $600 for TCM replacement.