Technical Description of OBD-II Trouble Code
The circuit for the Transmission Fluid Pressure Sensor/Switch “F” is experiencing low voltage.
What does that mean?
This generic powertrain/engine diagnostic trouble code is applicable to all OBD-II equipped vehicles, including but not limited to Chevrolet, Acura, Honda, Saturn, Jeep, Toyota, etc.
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 signal to other controllers using the vehicle’s data communication bus.
The PCM/TCM uses this voltage signal to determine transmission operating pressure and when a shift is occurring. This code is triggered when the “F” input does not match the normal operating voltages stored in the PCM/TCM’s memory. It may also indicate internal mechanical issues within the transmission. Consult a vehicle-specific repair manual to identify the “F” circuit for your particular vehicle.
P0994 typically indicates an issue with the electrical circuit (TFPS sensor circuit). This should not be overlooked during the troubleshooting process, especially when dealing with intermittent problems.
Troubleshooting steps may vary depending on the manufacturer, type of TFPS sensor, and wire colors.
Other related transmission fluid pressure sensor “F” circuit codes include:
Code Severity & Symptoms
The severity of the issue 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 P0994 engine code may include:
Causes
The most common causes for this code to be triggered are:
Diagnostic and Repair Procedures
A good starting point is to check for technical service bulletins (TSB) specific to your vehicle. Your issue may be a known problem with a known fix provided by the manufacturer, which can save you time and money during diagnosis.
Next, locate the Transmission Fluid Pressure Sensor/Switch (TFPS) on your vehicle. The TFPS is usually attached to the side of the valve body inside the transmission, although it may sometimes 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. Disconnect the connector and carefully inspect the terminals inside for any signs of burning or corrosion. If necessary, clean the terminals using electrical contact cleaner and a plastic bristle brush. Apply electrical grease to the terminals before reconnecting.
If you have a scan tool, clear the diagnostic trouble codes from memory and check if the P0994 code returns. If it does not, then the issue was most likely related to the connections.
This is the area of greatest concern for this code, as external transmission connections are prone to corrosion issues.
If the P0994 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 Digital Voltmeter to the signal terminal at the TFPS sensor wiring harness connector. Turn the Key On Engine Off and 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 the resistance 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 P0994 code persists, it is likely that the TFPS sensor has failed. However, a failed PCM/TCM or internal transmission malfunctions cannot be ruled out 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.
