The ECU controls shift solenoids by sending an electrical current through a coil of wire that is wrapped around the plunger mechanism inside the solenoid. If the computer detects an unusually low voltage situation somewhere along the shift solenoid C control circuit, it will store a P0979 DTC.
How Serious is the Code?
The P0979 diagnostic trouble code gets triggered when the ECU is having problems controlling the C (a.k.a. number three) shift solenoid. The transmission problems related to this OBDII code may not be very severe at first. But they will continue to get worse, and eventually render a nonworking transmission.
Symptoms of a P0979 include:
- Unusually harsh
- Transmission may not shift into gear
- Low transmission fluid level
- Dirty transmission fluid/filter
- Corroded/broken connectors and/or damaged wiring
- The shift solenoid has malfunctioned
How to Diagnose the Code?
Diagnosing a P0979 OBDII code should begin with a check of the transmission fluid. If it’s dirty or low, this OBD2 code will be triggered. Damage wiring or broken/corroded connectors can also cause problems with a solenoid. If none of these issues are present, then the shift solenoid C itself will need to be tested.
What Repairs Will Fix P0979?
- Service the transmission
- Replace or repair damage wiring/connectors
- Replace shift solenoid
- P0978 – Shift Solenoid “C” Control Circuit Range/Performance
- P0980 – Shift Solenoid “C” Control Circuit High