P0871 Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance

P0871 indicates range or performance trouble in transmission fluid pressure sensor or switch C. The pressure signal is wrong for expected operating conditions.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not assume the pressure sensor is bad from a range code; actual hydraulic pressure faults can look the same.

Symptoms of P0871

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0871

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Compare pressure sensor C data with commanded pressure, gear state, shift timing, slip data, and fluid temperature.
Inspect fluid condition, filter restriction, valve-body issues, pressure sensor wiring, and connector condition.
Check companion ratio, pressure-control, and solenoid codes that can explain the pressure mismatch.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.