P0979Shift Solenoid C Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Low-voltage fault, usually a short to ground, in the control circuit of shift solenoid C. GM uses it mainly on the Allison 1000 six-speed of its heavy pickups and chassis cabs: in 2016 a ground short of 0.22 ohm or less, stricter than the 0.42 ohm for SS1 and SS2, or an open of 200 kOhm or more counts after 10 samples (250 ms, Type A). From 2022 the open moves to P097C and P0979 needs an intrusive low-side test (120 ms, MIL after one trip). The Allison PS3 pressure switch test (P0872) also points to P0979 when its fault is electrical. Ford uses it for SSC short to ground beside P0760 open; on 6R80 and 6F, SSC drives the CB26 clutch. High side is P0980.
- What you may notice
- MIL on after the first faulty trip
- Transmission holds a default gear
- Rough or delayed shifts involving the affected clutch
- Likely causes
- LikelySolenoid C control wire shorted to ground
- PossibleInternal short of solenoid C inside the valve body
- PossibleOpen coil on GM 2016 Allison calibrations, which report opens under this code
- RareFaulty low-side driver in the control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.