Powertrain, generic (extended)

P27A7 Pressure Control Solenoid A Data Incompatible

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

P27A7 means the transmission controller holds no usable calibration curve for pressure control solenoid A. Each valve body is measured at the factory, and GM writes its current-to-pressure data into TCM memory; at every start-up the module checks that record. GM's 2020 table 20OBDG04 flags it when the data are missing after a replacement or brand-new TCM is fitted, belong to another solenoid class, fail the checksum, or contain axis points that fall instead of rise, rated Type A after one trip. On the nine-speed valve A is line pressure, on the ten-speed clutch C1, on the CVT the secondary pulley; the 2019 hybrid table 19OBDG01 lists it in the HPC1 too. The MIL comes on, and shifting is usually rough until the data are reprogrammed.

Likely causes

New or service TCM installed without loading the solenoid characterization data

Valve body replaced but the data for its part number not written to the TCM

Data set for a different solenoid class or valve body entered

Programming aborted, leaving a corrupted block (checksum error)

Symptoms

MIL on right after start-up
Harsh engagements or firm shifts from imprecise line pressure
Transmission may run a substitute program

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 atcm

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