P0978: Shift Solenoid C Control Circuit Range/Performance
Standardized SAE J2012 code · P09xx — Transmission
What does P0978 mean?
Range/performance fault in the drive circuit of shift solenoid C. GM's 2007 Allison 1000 table used it for an open SS3 circuit, but only while the commanded gear is not reverse trim, 5th or 6th; the table even prints the label Circuit Low beside an open-circuit test, an apparent typo. FCA lists P0978 among the four codes that the 2014–2016 9-speed transaxle set under old software when the range sensor harness had poor crimps. Ferrari's DCT bulletin uses it for a missing signal from the actuator 4 engage position sensor. Ford and GM six-speeds do not use it. Low/high are P0979/P0980, the current open code P097C.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
Symptoms
- MIL or transmission warning on
- Sudden neutral or default gear while driving
- Erratic or missing shifts
Common causes
- High Intermittent high resistance at crimped harness terminals (FCA 9-speed)
- Medium Open coil of shift solenoid C (Allison-type usage)
- Medium Transmission software that predates the manufacturer's fix
- Low Faulty driver stage in the transmission control module
Likelihood is a general estimate across vehicles; your make and model may differ.
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