P222E: Barometric-pressure sensor B changes too erratically

P222E detects a noisy or erratic barometric-pressure B signal in GM's 2015 OBDG06 table. The monitor evaluates how much the signal changes over time. It is not simply a test that ambient pressure is higher or lower than a fixed altitude-related limit.

The 100-kPa value is accumulated movement

The controller calculates the absolute difference between the current BARO2 reading and the reading 12.5 milliseconds earlier. It sums those changes across 80 consecutive readings into a quantity the table calls string length. A total above 100 kPa is the failure region.

Each resulting sample spans one second, and four failures out of five samples establish the diagnostic. Because the differences are absolute, alternating up-and-down noise accumulates even if the average pressure appears plausible. A nearly correct average can therefore coexist with a genuinely erratic signal.

Review the time trace, not only the average

Capture enough signal history to see repeated fluctuations at the relevant timescale. Distinguish a steadily biased pressure value from rapid variation around a believable value: the former and latter are different diagnostic patterns, and this monitor specifically addresses variation.

Verification should demonstrate that excessive accumulated changes have stopped and that the monitor completes after the actual cause is addressed. The table does not identify whether a sensor, connection, supply or processing issue produced the noise. Do not interpret its 100-kPa accumulated threshold as an allowable single pressure reading or a universal BARO sensor voltage specification. These details are limited to the documented GM implementation.

Source: GM diagnostic parameters, physical PDF page 537.