P27A8 code meaning
Pressure Control Solenoid B Data Incompatible
Powertrain system Generic code P27xx codes Check engine light
What P27A8 means
With P27A8 the TCM rejects the stored characterization record of pressure control solenoid B. GM's 2016 eight-speed table 16OBDG03 ties B to clutch 2 (CB12345R) and logs the code within one trip when that record is marked as not programmed. From 2017 on (17OBDG04, 18OBDG04, 20OBDG04) the letter stands for the converter clutch valve of the nine-speed, clutch C2 of the ten-speed and the primary pulley of GM's CVT, checked once during controller initialization and rated Type A. A blank or mismatched block nearly always follows a module swap or valve body job where the part-number-based download was skipped. Expect the MIL; lock-up or shift quality may suffer until the data are written.
P27A8 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 P27A8
- MIL illuminated
- Converter lock-up shudder or no lock-up on the nine-speed
- Uneven upshifts involving the affected clutch
Common causes of P27A8
- Most likelyCharacterization download skipped after TCM or valve body replacement
- PossibleData loaded for the wrong valve body part number
- Less likelyTCM non-volatile memory corrupting the stored block
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Pressure control solenoid bTCM
What each part of P27A8 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. |
| A8 | The exact fault in that area. |
What to do next
- Note P27A8 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 P27A8
What does P27A8 mean?
P27A8 means "Pressure Control Solenoid B Data Incompatible". With P27A8 the TCM rejects the stored characterization record of pressure control solenoid B. It is a generic code, so it means the same on every make.
Is it safe to drive with P27A8?
Drive gently and only to a workshop. With P27A8 the car can go into limp mode (reduced power) to protect itself.
Will P27A8 fail an emissions test?
Yes, it can. P27A8 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 P27A8 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 P27A8 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.