Powertrain, generic (extended)

P27A8 Pressure Control Solenoid B Data Incompatible

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

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.

Likely causes

Characterization download skipped after TCM or valve body replacement

Data loaded for the wrong valve body part number

TCM non-volatile memory corrupting the stored block

Symptoms

MIL illuminated
Converter lock-up shudder or no lock-up on the nine-speed
Uneven upshifts involving the affected clutch

Repair estimate

DifficultyShop_onlyWorkshop job

Parts and labour€100–400

Time0.5–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

pressure control solenoid btcm

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com.