P0879 Transmission Fluid Pressure Sensor/Switch D Circuit Malfunction

P0879 – OBD-II Trouble Code Technical Description

Transmission Fluid Pressure Sensor/Switch D Circuit Intermittent

What does the fault code mean P0879?

This diagnostic trouble code (DTC) is a generic transmission code. The P0879 code is considered a common code because it applies to all makes and models of vehicles. However, the specific repair steps may vary slightly depending on the model.

Trouble Code P0879 - Transmission Fluid Pressure Sensor/Switch.

The transmission fluid pressure sensor (TFPS) is typically mounted on the valve body inside the transmission. However, in some vehicles it may be screwed into the crankcase or transmission.

The TFPS converts mechanical pressure from the transmission into an electrical signal that is sent to the transmission control module (PCM). Typically the PCM/TCM informs other controllers using the vehicle data bus.

The PCM/TCM receives a voltage signal to determine transmission operating pressure or when shifting gears. This code sets if the "D" input does not match the normal operating voltage stored in the PCM/TCM memory.

Sometimes the problem can be due to mechanical problems within the transmission. But most often, the P0879 code is a problem with the TFPS sensor electrical circuit. This aspect should not be overlooked, especially if it is an occasional problem.

Troubleshooting steps may vary depending on the manufacturer, TFPS sensor type, and wire color.

Possible reasons

The P0879 code may indicate one or more of the following problems:

• Short to ground in the TFPS sensor signal circuit.
• TFPS sensor failure (internal short circuit).
• Transmission fluid ATF contaminated or low level.
• Clogged or blocked transmission fluid passages.
• Mechanical fault in the gearbox.
• Faulty TFPS sensor.
• Problem with internal mechanical transmission.
• Faulty PCM.

What are the symptoms of a fault code? P0879?

Driver symptoms of P0879 may include:

• MIL (malfunction indicator) lights up.
• The “Check Engine” light appears on the dashboard.
• The car starts moving immediately in 2nd or 3rd gear (emergency mode).
• Difficulty shifting gears.
• Harsh or hard shifts.
• Transmission overheating.
• Problems with the torque converter lock-up clutch.
• Increased fuel consumption.

This is a serious problem and it is recommended to fix it as soon as possible. Failure to act can lead to more complex and costly repairs.

How to diagnose a fault code P0879?

To start, always check your vehicle's Technical Service Bulletins (TSBs). Problem P0879 may already be a known issue with a known fix released by the manufacturer. This can save time and money during diagnosis.

The next step is to locate the transmission fluid pressure sensor (TFPS). Once found, visually inspect the connector and wiring. Look for scratches, dents, exposed wires, burns, or melted plastic. Disconnect the connector and carefully inspect the terminals inside the connector. Check to see if they look burnt or have a green tint indicating corrosion. If the terminals need to be cleaned, use electrical contact cleaner and a plastic brush. Let dry and apply electrical grease to the contact surfaces of the terminals.

Use a scan tool to clear the trouble codes and check to see if the P0879 code returns. If the code returns, you need to check the TFPS sensor and its associated circuitry. If necessary, inspect and replace related components such as power and ground wires, or the TFPS itself. If after all the checks the P0879 code still returns, a more in-depth diagnosis will be required, including possible replacement of the PCM/TCM or even internal transmission components. Uncertainty during the diagnostic process may require the assistance of a qualified automotive diagnostician.

Diagnostic errors

Some common pitfalls when diagnosing the P0879 trouble code may include problems with the transmission fluid pressure sensor (TFPS) itself, electrical connection problems, corrosion at the connector terminals, and mechanical problems with the transmission itself. In addition, problems with the engine control module (PCM/TCM) can also lead to misdiagnosis.

How serious is the fault code? P0879?

Trouble code P0879 is serious because it indicates problems with the transmission control system. This may result in changes in gear shift quality, vehicle driving behavior, or other transmission problems. It is recommended that this problem be addressed promptly to avoid more serious damage to the transmission and additional repair costs.

What repair will help eliminate the code? P0879?

To resolve DTC P0879, the following steps are recommended:

1. Check the transmission fluid pressure sensor (TFPS) connector and wiring for damage, corrosion, or blockage.
2. Clean and service the sensor connector terminals using electrical contact cleaner and electrical grease.
3. Check the voltage and resistance of the TFPS sensor, as well as its functionality when there is no pressure.
4. Replace the TFPS sensor if damaged or faulty and ensure the PCM/TCM is programmed or calibrated for the vehicle.

The repairs needed may vary depending on the specific problem found during the transmission diagnostic process.

What is P0879 Engine Code [Quick Guide]

P0879 – Brand-specific information

Code P0879 refers to transmission fluid pressure sensor/switch (TFPS) information. Here are some car brands and their interpretations for code P0879:

1. Dodge/Chrysler/Jeep: Transmission Fluid Pressure Sensor/D Switch Circuit
2. General Motors: Transmission Fluid Pressure Sensor/Switch “D” Circuit - Low Signal
3. Toyota: Transmission Fluid Pressure Sensor/Switch “D” Circuit - High Signal

These are some examples of P0879 decodings for specific car brands.