What Does It Mean?
This generic powertrain/drivetrain diagnostic trouble code generally applies to all OBD-II-equipped engines but appears more frequently in certain Dodge/Chrysler/Jeep, General Motors, and Toyota vehicles.
The Transmission Fluid Pressure Sensor/Switch (TFPS) is typically found attached to the side of the valve body inside the transmission, although sometimes it may be found screwed into the side of the transmission case/body itself.
The TFPS converts mechanical transmission pressures into an electrical signal for the Powertrain Control Module (PCM) or Transmission Control Module (TCM). Typically, the PCM/TCM will then inform other controllers using the vehicle’s data communication bus.
The PCM/TCM receives this voltage signal to determine the transmission’s operating pressure or when a change occurs. This code is set if this input does not match the normal operating voltages stored in the PCM/TCM’s memory.
P0878 is typically an electrical circuit issue (TFPS sensor circuit). This cannot be ignored during the troubleshooting phase, especially when it is an intermittent problem.
Troubleshooting steps may vary depending on the manufacturer, the type of TFPS sensor, and the wire colors.
Related Transmission Fluid Pressure Sensor D Codes:
- P0875 Transmission Fluid Pressure Sensor/Switch, “D” Circuit
- P0876 Transmission Fluid Pressure Sensor/Switch “D” Circuit Range/Performance
- P0877 Transmission Fluid Pressure Sensor/Switch “D” Low
- P0879 Transmission Fluid Pressure Sensor/Switch, “D” Circuit Intermittent
Code Severity and Symptoms
The severity depends on the circuit where the failure occurred. Since it is an electrical failure, the PCM/TCM may compensate to some extent. The failure could mean that the PCM/TCM alters the transmission shift if it is electronically controlled.
Symptoms of a P0878 engine code may include:
- Malfunction Indicator Lamp (MIL) illuminated
- Change in shift quality
- Vehicle starts in 2nd or 3rd gear (limp mode)
Causes
Typically, the causes for this code to set are as follows:
- Short to power in the TFPS sensor signal circuit – possible
- Open circuit to ground of the TFPS sensor – possible
- Failed/internally shorted TFPS sensor – probable
- Failed PCM – unlikely (programming required after replacement)
Diagnostic and Repair Procedures
A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your issue might be a known problem with a known fix published by the manufacturer and could save you time and money during diagnosis.
A good example of this would be if there are known codes related to power supply with P0878, or if there is more than one set of pressure sensor/switch codes. If so, start your diagnosis with the power-related trouble code or the multiple code diagnostic first, as this might be the reason for P0878.
Next, locate the Transmission Fluid Pressure Sensor/Switch (TFPS) on your specific vehicle. The TFPS is typically found attached to the side of the valve body inside the transmission, although it is sometimes screwed into the side of the transmission case/body itself. Once located, visually inspect the connector and wiring. Look for scratches, rubbing, exposed wires, burns, or melted plastic. Disconnect the connector and carefully inspect the terminals (the metal parts) inside the connector. Check if they appear burnt or have a greenish tint indicating corrosion, especially if they are mounted outside the transmission case. Use an electrical contact cleaner and a plastic-bristled brush if cleaning the terminals is necessary. Let it dry and apply electrical grease where the terminals make contact.
If you have a scan tool, clear the diagnostic codes from the memory and see if the P0878 code returns. If it does not, the connections were likely your problem.
This is the most common area of concern for this code, as external transmission connections have the highest incidence of corrosion issues.
If the P0878 code returns, we will need to test the TFPS sensor and its associated circuits. With the key off, disconnect the electrical connector from the TFPS sensor. Connect a black wire from the Digital Volt Ohm Meter (DVOM) to the ground or low reference terminal at the TFPS sensor wiring harness connector. Connect the red wire from the DVOM to the signal terminal at the TFPS sensor wiring harness connector. Turn the key to the engine-off position. Check the manufacturer’s specifications; the voltmeter should read 12 volts or 5 volts. Wiggle the connections to see if they change. If the voltage is incorrect, repair the power or ground wire or replace the PCM/TCM.
If the previous test was successful, connect one wire of an ohmmeter to the TFPS sensor’s signal terminal and the other wire to the ground or low reference terminal of the sensor. Check the manufacturer’s specifications for the sensor’s resistance to accurately test the resistance to pressure when no pressure is applied. Wiggle the Transmission Fluid Pressure Sensor/Switch connector while monitoring the resistance. If the ohmmeter readings do not pass, replace the TFPS.
If all previous tests were successful and you continue to get a P0878, this would most likely indicate a faulty TFPS sensor, although a faulty PCM/TCM cannot be ruled out, nor can internal transmission malfunctions until the TFPS sensor has been replaced. If in doubt, seek assistance from a qualified automotive diagnostician. PCMs/TCMs need to be programmed or calibrated to the vehicle to be installed correctly.