2251 real customers worldwide
Technical Description of OBD-II Trouble Code
The circuit for the Transmission Fluid Pressure Sensor/Switch “C” is registering a high voltage.
What does that mean?
This generic diagnostic trouble code is applicable to all OBD-II equipped vehicles, including but not limited to Dodge, Chrysler, Chevrolet, GMC, Acura, Toyota, etc. However, it is most commonly observed in Honda 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 signal to other controllers via the vehicle’s data communication bus.
The PCM/TCM uses this voltage signal to determine the transmission’s operating pressure and when a shift is occurring. This code is triggered if the voltage input for the “C” circuit does not match the normal operating voltages stored in the PCM/TCM’s memory. Consult a vehicle-specific repair manual to identify the “C” circuit for your particular vehicle.
P0873 typically indicates an issue with the electrical circuit of the TFPS sensor. It is important not to overlook this during the troubleshooting process, especially when dealing with an intermittent problem.
Troubleshooting steps may vary depending on the manufacturer, type of TFPS sensor, and wire colors.
Other related transmission fluid pressure sensor “C” 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 P0873 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. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
For example, if there are any known power-related codes set along with the P0873, 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 these may be the underlying cause of the P0873.
Next, locate the Transmission Fluid Pressure Sensor/Switch (TFPS) on your vehicle. It is usually found 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 P0873 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 P0873 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. Use a Digital Voltmeter (DVOM) to measure the voltage between the ground or low reference terminal and the signal terminal at the TFPS sensor wiring harness connector. With the Key On and the Engine Off, the voltmeter should read either 12 volts or 5 volts according to the manufacturer’s specifications. Wiggle the connections to see if the voltage changes. If the voltage is incorrect, repair the power or ground wire, or replace the PCM/TCM.
If the previous test passes, use an ohmmeter to measure the resistance between the signal terminal and the ground or low reference terminal at the TFPS sensor. Check the manufacturer’s specifications for the resistance of the sensor when no pressure is applied to it. Wiggle the connector at the Transmission Fluid Pressure Sensor/Switch while monitoring the resistance. If the ohmmeter readings do not meet the specifications, replace the TFPS.
If all previous tests pass and the P0873 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 is replaced. If unsure, seek assistance from a trained automotive diagnostician. PCM/TCMs must be programmed or calibrated to the vehicle for proper installation.
Professional Service
While we always recommend resolving this issue through mechanical means, if that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you are interested in this option, please upload your ECU file to our portal.
