P057C: low brake-position samples and the zero-position fallback

P057C is the low-input brake-pedal position monitor in both cited GM tables. The strategy describes detection of a short to ground and uses a sampled low-value decision. It does not provide a complete circuit test or prove which physical part caused that low value.

Read the threshold correctly

Both examples show a failure threshold of 5.00 and a decision of 20 failing samples out of 32. The row does not label the threshold as volts, so treating it as a 5-volt test limit would invent a unit. The supported conclusion is that enough samples fell below the monitor's calibrated lower boundary.

A momentarily low displayed value is consequently weaker evidence than a repeated low signal during conditions in which the diagnostic is enabled. Conversely, a normal reading after the event does not erase a previously accumulated failure. Capture the original status and signal history when available.

Fallback changes interpretation

The documented action sets brake-pedal position to zero percent. That substituted value can resemble a released pedal even when it is not an independent measurement. Distinguish the raw sensor information, where the service tool exposes it, from a calculated or substituted brake-position value.

Both examples classify P057C as a one-trip Type A fault. Correct verification requires the low-input condition to be absent and the relevant diagnostic to pass, not merely a convincing-looking zero-percent PID. Because this input concerns braking, circuit assessment belongs within the applicable professional service procedure; do not bypass it to regain another function.

Source and applicability

Documented monitors in gm-2025-03a, gm-2025-04b, model year 2025. These are module/calibration examples; vehicle, engine and transmission applicability must be confirmed independently. GM 2025-03a, page 342. GM 2025-04b, page 561.