P27A9: Solenoid C calibration data fails completeness or integrity checks

P27A9 is a stored-characterization diagnosis for pressure-control solenoid C in the reviewed GM transmission table. The listed functions are GF9 C1 CB123456 clutch control, GR10 C3 C23457910 clutch control, or CVT line control. Confirm the actual transmission before attaching a physical function to the letter C.

A checksum fault is different from a circuit fault

The controller compares the characterization region's calculated checksum with the value established when it was programmed. A mismatch makes the programming status invalid. This finding concerns data integrity; a passing solenoid continuity check does not answer it.

Other documented paths are unprogrammed or incomplete data, a solenoid-class mismatch, and axis values that do not remain nondecreasing. P27A9 alone does not reveal which of these paths failed, so preserve any additional programming or diagnostic detail available.

Match data to the installed assembly

The source states that characterization is associated with the valve-body assembly part number at manufacture and is programmed accordingly after valve-body service. Reviewing that identity is therefore more directly relevant than assuming every calibration code means the controller hardware has failed.

The monitor runs once during normal power-up initialization, before the regular control loop. Verification should include that startup opportunity after the applicable data problem is resolved.

Accepted characterization and no returning initialization fault are the relevant outcomes. The table lists Type A, one-trip behavior but does not establish hydraulic line pressure, clutch condition or a required solenoid-C replacement.

Source and applicability

Confirm the vehicle, transmission variant and relevant module before applying this monitor description. GM diagnostic table, PDF page 1202. GM diagnostic table, PDF page 1203.