P2123: Accelerator pedal sensor 1 signal exceeds the reference-scale limit

P2123 is an excessive APP1 signal diagnosis in the reviewed GM monitor. The source identifies the first accelerator pedal position channel, whereas the generic name uses sensor D. That distinction helps keep pedal-input testing separate from throttle-position testing.

What high means here

The failure boundary is APP1 above 95% of the reference scale; the table defines the full scale as five volts. It does not mean that pressing the pedal beyond 95% travel is a fault. The controller is evaluating the electrical signal's permitted range.

Monitoring requires run/crank voltage above 6.41 V and no associated reference-voltage fault, identified as P06A3 in the row. An apparently missing test result under low supply voltage or with a reference fault is not proof that the APP circuit is healthy.

Use the timing evidence

The strategy detects continuous or intermittent short-high behavior. It counts either 19 failures in a 39-count window or 14 continuous failures, at 12.5 milliseconds per count. Capturing a brief high excursion is therefore more useful than relying exclusively on a steady reading obtained after the event.

Correlate the electrical APP1 data with reference status before deciding that the pedal assembly is responsible. The table establishes the abnormal signal direction, not the location of the electrical fault. Verify repair by observing a permitted APP1 signal throughout the relevant operation and confirming that the enabled diagnostic no longer recurs. This documented Type A, one-trip behavior is calibration-specific.

Source and applicability

This explanation is limited to the documented 2025 GM monitor; its thresholds are not universal vehicle specifications. GM diagnostic table, PDF page 598.