P0878 Transmission Fluid Pressure Sensor/Switch D Circuit High

P0878 points to pressure sensor or switch D circuit high. The D pressure input is above the expected range, open, or shorted to voltage.

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 the sensor before confirming whether the high signal is caused by wiring or connector faults.

Symptoms of P0878

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 P0878

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

Check sensor D signal voltage, ground, reference circuit, open-circuit faults, short-to-voltage faults, and connector terminal tension.
Compare pressure sensor D data with pressure-control command, shift feel, actual pressure if available, and related sensor codes.
Inspect transmission case connector, internal harness, fluid intrusion, and wiring disturbed during recent transmission service.

Related OBD-II codes

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