P227C: BARO sensor C reports pressure below its allowed range

P227C is the low-pressure plausibility check for the BARO C channel in the reviewed GM table. The channel's pressure reaches the ECM through the MAF sensor over LIN, so the diagnostic is not simply a conventional low-voltage test at an external BARO signal wire.

Identify the C channel before testing

The source describes a pressure transducer whose output is proportional to absolute pressure, followed by digital reporting through the MAF sensor. Established LIN communication is a prerequisite. The failure criterion is reported BARO C below 50 kPa.

The C designation identifies the monitored channel; this summary does not establish a physical location or prove that a separately displayed BARO value is the same signal. Confirming that parameter mapping is an important first decision when scan data includes multiple pressure values.

A sustained reporting problem

The controller evaluates one sample every 25 milliseconds and requires 160 failures out of 200. This persistence rule means a fleeting displayed value cannot automatically be equated with the completed diagnostic.

Compare the correct absolute-pressure reading with an appropriate ambient reference and retain LIN status. A low value arriving in valid messages is different evidence from missing communication or a mislabeled scan parameter. These comparisons guide investigation without locating the failed component by themselves.

Verification should establish credible BARO C reporting during an enabled monitor window. The source documents Type A, one-trip behavior, but provides no pinout, universal analog-voltage limit or mandatory MAF replacement.

Source and applicability

Use these facts only after confirming the documented system and calibration for the vehicle. GM diagnostic table, PDF page 633.