P27AC code meaning
Pressure Control Solenoid F Data Incompatible
Powertrain system Generic code P27xx codes Check engine light
What P27AC means
P27AC reports invalid calibration data for pressure control solenoid F. On GM's 2016 eight-speed this is the line pressure solenoid, and the TCM logs the fault in one trip once the data are found unprogrammed. Later GM tables assign F to the nine-speed's C4 clutch, the ten-speed's C6 clutch and the CVT's binary pump; the 2025 table 25OBDG03A still carries the check, with the same start-up test and Type A rating. Because line pressure or pump control rides on this valve in some layouts, a bad record can affect every gear, not just one shift. Typical triggers are a replacement controller or valve body installed without the data download; a faulty solenoid coil sets circuit codes instead.
P27AC 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 P27AC
- MIL on
- Firm or soft shifts throughout when line pressure depends on valve F
- Possible fixed-gear substitute mode
Common causes of P27AC
- Most likelyTCM swapped and solenoid F data never loaded
- PossibleRemanufactured valve body with a new ID not entered into the TCM
- Less likelyData block damaged by a voltage drop during programming
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Pressure control solenoid fTCM
What each part of P27AC 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. |
| AC | The exact fault in that area. |
What to do next
- Note P27AC 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 P27AC
What does P27AC mean?
P27AC means "Pressure Control Solenoid F Data Incompatible". P27AC reports invalid calibration data for pressure control solenoid F. It is a generic code, so it means the same on every make.
Is it safe to drive with P27AC?
Drive gently and only to a workshop. With P27AC the car can go into limp mode (reduced power) to protect itself.
Will P27AC fail an emissions test?
Yes, it can. P27AC 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 P27AC 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 P27AC clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.