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 triggered when the powertrain control module (PCM) detects an intermittent problem with the transmission fluid pressure sensor or switch, which plays a crucial role in monitoring the transmission fluid pressure. When this sensor fails or provides inconsistent readings, it can lead to various transmission issues, including erratic shifting and potential transmission failure. Understanding the causes, symptoms, and repair methods for this code is essential for vehicle owners and DIY mechanics.
| P0879 Code Meaning | P0879 Code Common Causes |
|---|---|
| Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit Intermittent | Faulty transmission fluid pressure sensor |
| Intermittent signal issues from the sensor | Wiring or connector problems |
| PCM malfunction | Low or contaminated transmission fluid |
| Internal mechanical issues in the transmission | Corroded or damaged connectors |
Symptoms of P0879 Code
When the P0879 code is present, vehicle owners may notice several symptoms that can indicate underlying issues with the transmission system:
- Malfunction Indicator Light (MIL) On: The check engine light will typically illuminate when this code is detected.
- Change in Shift Quality: Drivers may experience harsh or erratic shifting as the transmission struggles to maintain proper fluid pressure.
- Limp Mode Activation: The vehicle may start off in second or third gear, limiting acceleration and performance to protect the transmission.
- Delayed Engagement: There may be a noticeable delay when shifting from park to drive or reverse.
Technical Explanations
The Transmission Fluid Pressure Sensor/Switch ‘D’ is responsible for monitoring the hydraulic pressure within the transmission. It sends this information to the PCM, which uses it to manage the shifting process effectively. A malfunction in this system can lead to:
- Incorrect Pressure Readings: If the sensor fails or provides intermittent signals, it can result in improper fluid pressure management.
- Transmission Control Module (TCM) Adjustments: The TCM may attempt to compensate for these incorrect readings by altering shift patterns, which can lead to further complications if not addressed.
Step-by-Step Diagnosis
Diagnosing a P0879 code involves a systematic approach to identify and resolve the underlying issues:
- Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes that might provide more context about the issue.
- Inspect Transmission Fluid: Check the level and condition of the transmission fluid. Low or dirty fluid can contribute to sensor malfunctions.
- Visual Inspection of Wiring and Connectors:
- Look for signs of wear, corrosion, or damage on the wiring harness connected to the transmission fluid pressure sensor.
- Ensure that all connectors are secure and free from moisture and debris.
- Test the Transmission Fluid Pressure Sensor:
- Disconnect the sensor and use a multimeter to test its resistance according to manufacturer specifications.
- If readings are outside acceptable ranges, consider replacing the sensor.
- Check for Ground Issues: Ensure that ground connections are clean and secure, as poor grounding can lead to intermittent faults.
- Clear Codes and Test Drive: After performing repairs, clear any stored codes and take the vehicle for a test drive to see if the P0879 code reappears.
Solution Methods
Addressing a P0879 code typically involves several potential solutions depending on what was identified during diagnosis:
- Replace Faulty Transmission Fluid Pressure Sensor: If testing confirms that the sensor is malfunctioning, replacing it is often necessary.
- Repair Wiring Issues: Fix any damaged wires or poor connections found during inspection.
- Change Transmission Fluid: If low or contaminated fluid was identified as an issue, perform a fluid change to ensure optimal performance.
- Replace PCM if Necessary: In rare cases where all other components are functioning properly but issues persist, consider testing or replacing the PCM.
Cost Estimates
The cost of repairs associated with a P0879 code can vary significantly based on several factors:
- Transmission Fluid Change: $100 – $250 depending on fluid type and labor costs.
- Transmission Fluid Pressure Sensor Replacement: $150 – $300 including parts and labor.
- Wiring Repairs: $50 – $200 depending on extent of damage and labor rates.
- PCM Replacement/Programming: $500 – $1500 depending on vehicle make/model and programming requirements.
Warnings and Recommendations
- Always ensure safety by disconnecting the battery before working on electrical components.
- If you are not confident in your ability to diagnose or repair these issues, it is strongly recommended to seek professional assistance from a certified mechanic.
- Regular maintenance of your vehicle’s transmission system can help prevent issues related to fluid pressure sensors in the future.
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 causes P0879?
Common causes include a faulty sensor, wiring issues, low transmission fluid levels, or internal mechanical problems. - Can I drive my car with a P0879 code?
While it may be possible, driving with this code can lead to erratic shifting and potential transmission damage. - How do I fix error code P0879?
Fixes typically involve inspecting/replacing the transmission fluid pressure sensor, repairing wiring issues, or changing transmission fluid. - Is P0879 serious?
This code can lead to serious transmission problems if not addressed promptly. - What should I do if my check engine light comes on?
Use an OBD-II scanner to read codes and diagnose any underlying issues. - How much does it cost to fix P0879?
The cost can range from $100 for fluid changes up to $1500 for PCM replacement. - When should I seek professional help?
If you’re unable to diagnose or resolve issues after basic troubleshooting steps, consult a professional mechanic.
In conclusion, understanding the P0879 trouble code is crucial for maintaining your vehicle’s performance. By following systematic diagnostic steps and addressing any identified issues promptly, vehicle owners can prevent further complications related to their transmission systems. Regular maintenance and awareness of symptoms will aid in ensuring long-term reliability and safety on the road.