The P0879 trouble code indicates an issue with the Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit Intermittent. This code is part of the OBD-II diagnostic system, which monitors various functions of the vehicle’s powertrain, including the engine and transmission. When the powertrain control module (PCM) detects that the transmission fluid pressure sensor is sending inconsistent signals, it triggers this code. Understanding and resolving the P0879 code is essential for maintaining optimal transmission performance and preventing further damage.
| P0879 Code Meaning | P0879 Code Common Causes |
|---|---|
| Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit Intermittent | Faulty transmission fluid pressure sensor |
| Indicates potential issues with fluid pressure monitoring | Wiring issues (damaged or corroded wires) |
| Can lead to erratic shifting behavior | Faulty transmission control module (TCM) |
| May affect overall vehicle drivability | Low or contaminated transmission fluid |
| Internal transmission problems |
Symptoms of P0879 Code
When the P0879 code is triggered, drivers may experience several symptoms that can affect vehicle performance:
- Malfunction Indicator Light (MIL) On: The check engine light will illuminate on the dashboard.
- Erratic Shifting: The vehicle may shift harshly or unpredictably between gears.
- Limp Mode Activation: The transmission may default to a limited gear range, often starting in second or third gear to protect the engine and transmission.
- Poor Acceleration: Drivers may notice sluggish acceleration due to improper gear shifting.
- Unusual Noises: Grinding or whining noises from the transmission can indicate internal issues.
Technical Explanation of P0879
The Transmission Fluid Pressure Sensor (TFPS) is crucial for monitoring the hydraulic pressure within the transmission. This sensor sends signals to the TCM, which adjusts shifting patterns based on fluid pressure readings. When the P0879 code appears, it indicates that the TFPS is experiencing intermittent faults, which can lead to incorrect pressure readings and ultimately affect shifting performance.
Step-by-Step Diagnosis
Diagnosing a P0879 code involves a systematic approach:
- Check for Additional Codes: Use an OBD-II scanner to determine if other related codes are present. This can provide insight into whether multiple issues are at play.
- Visual Inspection: Locate and inspect the TFPS and its wiring harness. Look for signs of damage, corrosion, or loose connections.
- Test Voltage Supply: With the ignition on but the engine off, use a digital voltmeter to check voltage at the TFPS connector. Compare readings against manufacturer specifications.
- Resistance Testing: Disconnect the TFPS and test its resistance using an ohmmeter. Ensure that it falls within specified limits when no pressure is applied.
- Check TCM Functionality: If all tests indicate that the TFPS is functioning correctly, assess the TCM for faults. This may require specialized diagnostic tools.
Solution Methods
Resolving a P0879 code typically involves several potential solutions:
- Replace Faulty TFPS: If testing confirms that the TFPS is faulty, replacing it is necessary. Ensure that you use OEM parts for compatibility.
- Repair Wiring Issues: If damaged or corroded wiring is found during inspection, repair or replace these components as needed.
- Address Fluid Issues: Check the transmission fluid level and condition. If it’s low or contaminated, perform a fluid change and refill to manufacturer specifications.
- Reprogram TCM: In cases where the TCM has been replaced or repaired, it may require reprogramming to ensure proper operation with the new components.
Cost Estimates
The cost of diagnosing and repairing a P0879 code can vary significantly based on location and vehicle type:
- Diagnostic Fees: Expect to pay between $100 to $150 for a professional diagnostic service.
- TFPS Replacement: The cost of a new TFPS can range from $50 to $200 depending on make and model, plus labor costs if you choose professional installation.
- Wiring Repairs: Simple wiring repairs might cost around $50 to $100, while extensive harness replacements could exceed $300.
Warnings and Recommendations
- Professional Help: If you’re not comfortable performing these diagnostic tests or repairs yourself, it’s advisable to seek help from a qualified mechanic.
- Avoid Driving with P0879 Code Active: Continuing to drive with this code can lead to more severe transmission damage and costly repairs down the line.
- Regular Maintenance: Regular checks of your vehicle’s transmission fluid levels and condition can help prevent issues like those associated with the P0879 code.
Frequently Asked Questions About P0879
- What does error code P0879 mean?
P0879 indicates an intermittent issue with the Transmission Fluid Pressure Sensor/Switch ‘D’, affecting how your vehicle monitors fluid pressure. - How serious is a P0879 code?
This code can lead to erratic shifting and potential transmission failure if not addressed promptly. - Can I drive my car with a P0879 code?
It’s not recommended as it may cause further damage; limp mode may engage to protect your vehicle. - What are common causes of P0879?
The most common causes include a faulty TFPS, wiring issues, low fluid levels, or internal transmission problems. - How do I diagnose a P0879 code?
Use an OBD-II scanner for initial diagnostics, inspect wiring and connectors, test voltage and resistance at the TFPS. - Is it safe to replace the TFPS myself?
If you have basic mechanical skills and tools, you can replace it; otherwise, consult a professional. - What tools do I need for diagnosing P0879?
A digital voltmeter (DVOM), an OBD-II scanner, and basic hand tools are essential for diagnosis. - Will clearing codes fix my car?
No, clearing codes will not fix underlying issues; it’s crucial to diagnose and repair before resetting codes.
Understanding and addressing a P0879 trouble code requires careful diagnosis of both electrical components and mechanical systems within your vehicle’s transmission. By following these guidelines, DIY mechanics can effectively troubleshoot this issue while ensuring their vehicle remains in safe operating condition. Regular maintenance and prompt attention to warning signs will help prevent future complications associated with this trouble code.