Technical Description of OBD-II Trouble Code
The transmission fluid pressure sensor/switch D circuit is registering a high voltage.
What does that mean?
This generic powertrain/engine diagnostic trouble code is applicable to all OBD-II equipped engines, but it is more commonly found in certain Dodge/Chrysler/Jeep, General Motors, and Toyota vehicles.
The transmission fluid pressure sensor/switch (TFPS) is typically located on the side of the valve body inside the transmission, although it may sometimes be screwed into the side of the transmission case/body itself.
The TFPS converts the mechanical transmission pressures into an electrical signal for the Powertrain Control Module (PCM) or Transmission Control Module (TCM). The PCM/TCM then communicates this information to other controllers through the vehicle’s data communication bus.
The PCM/TCM uses the voltage signal from the TFPS to determine the transmission’s operating pressure and when a shift is occurring. If the input voltage does not match the normal operating voltages stored in the PCM/TCM’s memory, this code is triggered.
P0878 typically indicates an issue with the electrical circuit of the TFPS sensor. It is important to address this during the troubleshooting stage, especially if dealing with an intermittent problem.
The troubleshooting steps may vary depending on the manufacturer, type of TFPS sensor, and wire colors.
Other related transmission fluid pressure sensor D codes include:
Code Severity & Symptoms
The severity of the code depends on which circuit the failure has occurred in. Since this is an electrical failure, the PCM/TCM can compensate to some extent. The failure may result in the PCM/TCM modifying the shifting of the transmission if it is electronically controlled.
Symptoms of a P0878 engine code may include:
Causes
The common causes for this code to be triggered are:
Diagnostic and Repair Procedures
A good starting point is to check for any technical service bulletins (TSB) specific to your vehicle. There may be a known issue with a known fix provided by the manufacturer, which can save time and money during diagnosis.
For example, if there are any known power-related codes set along with the P0878, or if there is more than one pressure sensor/switch code set, begin the diagnosis with the power-related fault code or the multiple code diagnosis, as they may be the reason for the P0878.
Next, locate the transmission fluid pressure sensor/switch (TFPS) on your vehicle. It is usually attached to the side of the valve body inside the transmission, but it may also be screwed into the side of the transmission case/body itself. Once located, visually inspect the connector and wiring for any signs of scraping, rubbing, bare wires, burn spots, or melted plastic. Separate the connector and carefully examine the terminals inside for any signs of burning or corrosion. If necessary, clean the terminals using electrical contact cleaner and a plastic bristle brush. After cleaning, apply electrical grease to the terminals.
If you have a scan tool, clear the diagnostic trouble codes from memory and check if the P0878 code returns. If it does not, then the issue was most likely related to the connections.
This is the most common area of concern for this code, as the external transmission connections are prone to corrosion issues.
If the P0878 code does return, further testing of the TFPS sensor and its associated circuits is necessary. With the key off, disconnect the electrical connector at the TFPS sensor. Connect a digital voltmeter (DVOM) black lead to the ground or low reference terminal at the TFPS sensor wiring harness connector. Connect the red lead of the DVOM to the signal terminal at the TFPS sensor wiring harness connector. Turn the key on, but keep the engine off. Check the manufacturer’s specifications; the voltmeter should read either 12 volts or 5 volts. Wiggle the connections to see if there are any changes. If the voltage is incorrect, repair the power or ground wire, or replace the PCM/TCM.
If the previous test passed, connect one lead of an ohmmeter to the signal terminal at the TFPS sensor and the other lead to the ground or low reference terminal at the sensor. Check the manufacturer’s specifications for the resistance of the sensor to accurately test its resistance to pressure when no pressure is applied. Wiggle the connector at the transmission fluid pressure sensor/switch while monitoring the resistance. If the ohmmeter readings do not pass, replace the TFPS.
If all previous tests have passed and the P0878 code persists, it is likely that the TFPS sensor has failed. However, a failed PCM/TCM cannot be ruled out, nor can internal transmission malfunctions, until the TFPS sensor has been replaced. If unsure, seek assistance from a trained automotive diagnostician. PCM/TCMs must be programmed or calibrated to the vehicle for correct installation.
