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 components of a vehicle’s powertrain. When the Powertrain Control Module (PCM) detects that the signal from the transmission fluid pressure sensor does not match expected values, it triggers the P0879 code. This can lead to various transmission-related issues, affecting vehicle performance and drivability.
| P0879 Code Meaning | P0879 Code Common Causes |
|---|---|
| Transmission Fluid Pressure Sensor/Switch “D” Circuit Intermittent | Failed Transmission Fluid Pressure Sensor (TFPS) |
| Electrical circuit issue in the TFPS | Corroded or damaged wiring/connectors |
| Internal mechanical failure in the transmission | Low transmission fluid levels |
| Faulty Powertrain Control Module (PCM) | Stuck or malfunctioning valve in the valve body |
| Inconsistent voltage signals from the TFPS | Transmission fluid leaks |
Symptoms of P0879 Code
The symptoms associated with the P0879 code can vary depending on the severity of the issue. Common symptoms include:
- Malfunction Indicator Light (MIL): The check engine light may illuminate on your dashboard.
- Change in Shift Quality: Drivers may experience harsh or erratic shifting behavior.
- Limp Mode Activation: The vehicle may start in second or third gear, limiting acceleration to protect the transmission.
- Transmission Slipping: There may be instances where the transmission slips out of gear unexpectedly.
Technical Explanation
The Transmission Fluid Pressure Sensor (TFPS) is responsible for monitoring the hydraulic pressure within the transmission. It converts hydraulic pressure into an electrical signal that is sent to the PCM or Transmission Control Module (TCM). The PCM uses this information to optimize shifting and overall transmission performance.
When there is a fault in this system, such as an intermittent signal from the TFPS, it can lead to incorrect pressure readings. This may cause erratic shifting, overheating, or even complete transmission failure if not addressed promptly.
Step-by-Step Diagnosis
Diagnosing a P0879 code involves a systematic approach to identify and rectify the underlying issue. Here’s a structured method:
- Check for Additional Codes: Use an OBD-II scanner to see if there are any related trouble codes that could provide more context.
- Inspect Wiring and Connectors:
- Visually examine the wiring harness connected to the TFPS for signs of damage, corrosion, or loose connections.
- Ensure that connectors are secure and free from moisture.
- Test Voltage at TFPS:
- With the ignition on (engine off), use a digital voltmeter to check for voltage at the TFPS connector.
- Refer to manufacturer specifications for acceptable voltage ranges (typically 5V or 12V).
- Check Resistance Values:
- Disconnect the TFPS and measure resistance using an ohmmeter.
- Compare readings with manufacturer specifications; significant deviations may indicate a faulty sensor.
- Inspect Transmission Fluid Levels:
- Ensure that the transmission fluid is at the correct level and is not contaminated.
- Low fluid levels can affect sensor readings and overall transmission performance.
- Mechanical Inspection:
- If electrical tests pass, inspect internal components such as valves and pumps within the transmission for wear or malfunction.
Solution Methods
Resolving a P0879 code typically involves one or more of the following solutions:
- Replace Faulty TFPS: If testing indicates that the sensor is defective, replace it with a new unit.
- Repair Wiring Issues: Fix any damaged wires or connectors found during inspection, ensuring all connections are secure.
- Fluid Change: If fluid levels are low or contaminated, perform a transmission fluid change and replace filters as necessary.
- Address Mechanical Failures: If internal components are found to be faulty, repairs may involve disassembling parts of the transmission for replacement.
- Reprogram PCM/TCM: If a new PCM or TCM is installed, ensure it is programmed correctly for your vehicle model.
Cost Estimates
The cost associated with diagnosing and repairing a P0879 code can vary significantly based on several factors:
- Diagnostic Fees: Expect to pay between $100 to $150 for professional diagnostics if you choose not to DIY.
- Parts Costs:
- Transmission Fluid Pressure Sensor: $50 to $150
- Wiring Repair Kits: $20 to $100
- Transmission Fluid Change: $100 to $200
- Labor Costs: Depending on your location and shop rates, labor can range from $75 to $150 per hour.
Overall repair costs can range from as low as $200 for simple fixes like fluid changes to over $1,000 if extensive repairs are needed.
Warnings and Recommendations
- Professional Help Needed: If you are unsure about diagnosing or repairing issues related to your vehicle’s transmission system, it is advisable to consult with a qualified mechanic. Incorrect repairs could lead to further damage and higher repair costs.
- Regular Maintenance: To prevent issues like P0879 from occurring, maintain regular checks on your vehicle’s transmission fluid levels and quality. Change fluids according to manufacturer recommendations.
- Monitor Symptoms Closely: If you notice any symptoms like erratic shifting or unusual noises from your transmission, address these concerns immediately before they escalate into more serious problems.
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. - Can I drive my car with a P0879 code?
While it may be drivable, it’s not advisable as it can lead to further transmission damage. - How do I reset a P0879 code?
You can reset it by clearing codes with an OBD-II scanner after addressing any underlying issues. - What are common symptoms of a failing TFPS?
Common symptoms include harsh shifting, slipping gears, and activation of limp mode. - Is replacing the TFPS difficult?
It can be straightforward for those familiar with automotive repair; however, professional help is recommended if unsure. - How often should I check my transmission fluid?
It’s best practice to check your transmission fluid every 30,000 miles or as recommended by your vehicle’s manufacturer. - What happens if I ignore a P0879 code?
Ignoring this code can lead to severe transmission damage and costly repairs down the line. - Are there any recalls related to P0879?
Check with your vehicle manufacturer for any recalls related to transmission issues that might affect your model.
In conclusion, understanding and addressing a P0879 trouble code promptly is crucial for maintaining optimal vehicle performance. By following systematic diagnostic steps and implementing appropriate solutions, vehicle owners can effectively manage this issue while ensuring their vehicles remain safe and reliable on the road.