P0978 Shift Solenoid C Control Circuit Range/Performance

P0978 indicates range or performance trouble in shift solenoid C control circuit. The commanded solenoid response does not match expected shift behavior.

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 an electrical failure when the code says performance; hydraulic response and fluid condition must be checked.

Symptoms of P0978

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 P0978

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 shift solenoid C command with actual gear ratio, shift timing, input speed, output speed, and pressure data.
Inspect fluid condition, valve-body sticking, solenoid response, control wiring, and connector condition.
Review whether the fault occurs hot, cold, during one shift, or under heavy throttle.

Related OBD-II codes

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