P27A9 code meaning
Pressure Control Solenoid C Data Incompatible
Powertrain system Generic code P27xx codes Check engine light
What P27A9 means
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.
P27A9 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P27A9
- 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
Common causes of P27A9
- Most likelyReplacement TCM fitted without solenoid C data
- Most likelyValve body or solenoid assembly swapped without updating the TCM
- Less likelyStored data corrupted, checksum no longer matches
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Pressure control solenoid cTCM
What each part of P27A9 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 7 | Area: transmission. |
| A9 | The exact fault in that area. |
What to do next
- Note P27A9 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P27A9
What does P27A9 mean?
P27A9 means "Pressure Control Solenoid C Data Incompatible". P27A9 concerns solenoid C. It is a generic code, so it means the same on every make.
Is it safe to drive with P27A9?
Drive gently and only to a workshop. With P27A9 the car can go into limp mode (reduced power) to protect itself.
Will P27A9 fail an emissions test?
Yes, it can. P27A9 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P27A9 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 1.5 hours of work. This is a job for a workshop.
Will P27A9 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.