P0870 Transmission Fluid Pressure Sensor/Switch C Circuit

P0870 points to transmission fluid pressure sensor or switch C circuit. The controller detected a fault in another pressure feedback channel.

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 replace transmission hydraulic parts before verifying pressure sensor C circuit and actual pressure behavior.

Symptoms of P0870

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 P0870

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, and other pressure sensor channels.
Inspect sensor C wiring, connector condition, reference voltage, ground, internal harness, and transmission case connector sealing.
Review fluid level and condition plus pressure-control, ratio, or shift-solenoid codes that may explain pressure readings.

Related OBD-II codes

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