P089B: Alpha 2 shifter position fails path or disagreement limits

P089B identifies a performance problem with the second X-position channel of the gear lever. GM labels the measured value Alpha 2. The reviewed monitor has an outside-path branch and a separate branch for percentage disagreement at or above the calibrated Alpha limit.

Channel number is part of the diagnosis

The code names sensor 2; P082A in the same document covers sensor 1. Those assignments help identify which reported channel is involved, but neither code alone proves that the named physical sensor is the sole cause of a correlation discrepancy. The measurement and its comparison context still matter.

The Alpha limit is a position-dependent percentage map, not one universal tolerance. The supporting values range from 7% to 20%. Applying the loosest value to every position could overlook a disagreement that the controller judges excessive in a tighter region.

Confirming the performance check

Calibration must enable the monitor, and 10 failures out of 12 samples qualify the fault. The row lists Type B, two-trip reporting without specifying the sample interval.

For verification, review Alpha 2 across the relevant movement path and compare disagreement against the correct map coordinates. A single normal endpoint reading is weaker evidence than successful traversal of the area where the fault occurred. The source gives no fixed sensor-voltage limits, wiring procedure or replacement instruction. The explanation is bounded to the documented 2025 GM shifter monitor; model and calibration coverage require vehicle-specific confirmation.

Source: GM monitor, PDF page 657; GM monitor, PDF page 1635.