What it means
The transmission fluid pressure sensor/switch C reports a circuit high fault. Hydraulic pressure feedback for shift control is unreliable on this channel.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Transmission pressure sensor/switch C supplies the control module with an electrical signal used to assess hydraulic pressure for shifting. P0873 sets when the C-circuit signal is higher than the module expects, commonly because the signal wire is shorted to battery voltage or the sensor circuit is open.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open sensor
- Connector pins corroded - high contact resistance
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and check live sensor C data to confirm the high signal and identify the gear or conditions when it occurs.
- Inspect sensor C's connector and harness for unplugged connections, broken wires, damaged insulation, or contact with a power feed.
- Check connector pins for corrosion or looseness and confirm the connector is fully seated.
- Use the wiring diagram to test the C signal wire for a short to battery voltage and check circuit continuity against the manufacturer's specification.
- If the harness and connections pass, test pressure sensor/switch C for an internal open or failed output using the vehicle's specified procedure.
Common fixes
- Reconnect and secure a loose sensor C connector.
- Repair damaged wiring or a signal wire shorted to battery voltage.
- Repair corroded or loose terminals that interrupt the C circuit.
- Replace pressure sensor/switch C if it has an internal open and the wiring is sound.
Can I keep driving?
Avoid towing, hard acceleration, and extended driving if shift quality is poor or the transmission slips or enters limp mode. Incorrect C-channel feedback can impair shift control, and slipping can cause further transmission damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.