P27A9Pressure Control Solenoid C Data Incompatible
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P27A9 concerns solenoid C. GM's controller compares the calibration it holds for this valve with the valve body actually fitted; if the block for C is absent, of the wrong device class, damaged or non-monotonic, the fault is stored at power-up and lights the MIL in that same trip (Type A in 20OBDG04 and in the 2025 table 25OBDG03A). Valve C feeds clutch C1 (CB123456) in the nine-speed, clutch C3 in the ten-speed and line pressure in the CVT; on the 2016 eight-speed it is clutch 3 (C13567). Without valid data the module cannot turn a pressure request into the right current, so clutch fill and shift timing for that element drift. The cure is loading the matching valve body data, not a new solenoid.
- What you may notice
- MIL on in the first drive after the fault
- Slipping or harsh application of the clutch fed by valve C
- On the CVT, unstable line pressure and belt slip risk
- Likely causes
- LikelyReplacement TCM fitted without solenoid C data
- LikelyValve body or solenoid assembly swapped without updating the TCM
- RareStored data corrupted, checksum no longer matches
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.