Transmission Fluid Pressure Sensor/Switch "C" Circuit High
P0873 indicates the transmission fluid pressure sensor/switch C circuit is reading a voltage that is too high. This occurs when the PCM detects an electrical signal above the expected range, typically caused by a short to power, a failed sensor, or a wiring issue in the circuit.
What You Might Notice
- Transmission shifting abnormalities or delayed shifts
- Check engine light illuminated
- Transmission may enter limp mode or default shift pattern
- Possible harsh or erratic downshifts
- No obvious drivability issues in some cases
Most Common Causes
- 1
Short to power in signal circuit
The transmission fluid pressure sensor signal wire may be shorted directly to battery voltage, causing the PCM to read a higher-than-normal voltage.
- 2
Failed transmission fluid pressure sensor
The TFPS sensor itself has failed or developed an internal short, causing it to send incorrect high voltage signals to the PCM.
- 3
Open or damaged ground circuit
A break or poor connection in the ground circuit to the sensor prevents proper signal return, causing the circuit to read high.
- 4
Wiring harness damage or corrosion
Corroded or damaged wiring connectors in the transmission fluid pressure sensor circuit can cause intermittent or constant high voltage readings.
How to Diagnose It
- 1
Check Short to power in signal circuit — The transmission fluid pressure sensor signal wire may be shorted directly to battery voltage, causing the PCM to read a higher-than-normal voltage.
- 2
Check Failed transmission fluid pressure sensor — The TFPS sensor itself has failed or developed an internal short, causing it to send incorrect high voltage signals to the PCM.
- 3
Check Open or damaged ground circuit — A break or poor connection in the ground circuit to the sensor prevents proper signal return, causing the circuit to read high.
- 4
Check Wiring harness damage or corrosion — Corroded or damaged wiring connectors in the transmission fluid pressure sensor circuit can cause intermittent or constant high voltage readings.
How to Fix It
- 1
Inspect and repair wiring harness
Inspect the transmission fluid pressure sensor wiring and connectors for damage, corrosion, or loose connections. Repair or replace damaged sections and clean corroded connectors.
- 2
Replace transmission fluid pressure sensor
Remove and replace the transmission fluid pressure sensor C with a new OEM or quality equivalent sensor. This is the most common fix for this code.
- 3
Check and repair ground connections
Locate the ground connection for the TFPS sensor circuit and verify it has a solid connection to the engine block or chassis ground. Clean corrosion and re-secure if loose.
- 4
Verify PCM/TCM after repairs
After replacing the sensor or repairing wiring, clear the code and test drive to confirm the fix. If the code persists, the PCM/TCM may require reprogramming or replacement by a dealership.
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