P2227: three-sensor comparison isolates barometric-pressure disagreement

P2227 is a barometric-pressure performance code. The reviewed 25OBDG04B implementation compares BARO, manifold absolute pressure and turbocharger-inlet air pressure in a three-sensor arrangement. It identifies BARO as the outlier when it disagrees with both other sensors while those two agree.

Running and stopped tests differ

During the running check, the permitted pressure difference comes from an airflow-dependent map. The supporting values rise from 10 kPa at 5 g/s to 43 kPa at 33 g/s. Thus one fixed 10-kPa tolerance is not valid for every running comparison.

The stopped-engine branch uses a 10-kPa pairwise agreement limit and also checks BARO against 50–115 kPa bounds. It requires more than five seconds since the relevant previous running condition and excludes listed active or pending pressure-sensor circuit faults.

Interpreting a repeat test

The running branch requires engine speed below 985 rpm, requested fuel below 25 mm³, measured throttle above 90%, coolant above 60°C and relay supply above 11 volts, with relevant companion faults absent. It qualifies 240 failures in 300 samples; the stopped branch uses four in five. Both use 12.5-millisecond sampling, and reporting is Type A, one trip.

Verification should record all three pressure values and identify which branch actually ran. A lone BARO reading cannot reproduce the outlier logic. These facts apply to the specified three-sensor 2025 GM monitor, not every P2227 implementation. Vehicle applicability and any sensor-replacement decision require separate service confirmation.

Source: GM monitor, PDF page 796; GM monitor, PDF page 797; GM monitor, PDF page 1627.