P24EF: Control-module wake-up output is open in its off state

P24EF identifies a control-module wake-up circuit/open fault. The 2018 GM HPC2/BSM monitor evaluates the output wake-up path while its command is off. It is a circuit diagnostic rather than a direct declaration that one named module has stopped communicating.

Why a middle voltage can identify an open

The documented open-circuit band is 2.82–7.04 V. The diagnostic must be enabled, and 480 failed samples among 560 are required. Samples occur every 12.5 milliseconds, producing a listed seven-second evaluation. GM classifies this implementation Type A, one trip.

A voltage inside that band is meaningful only in the appropriate circuit and command state. It should not be treated as a universal acceptable logic level or tested at an assumed connector pin.

Wake-up faults and communication faults are related questions

A module's availability can depend on its wake-up path, but P24EF does not identify a failed remote module. Preserve the off command, output feedback and any associated communication history. The exact vehicle's diagram is needed to establish which devices share the monitored output.

Following a circuit correction, confirm that the off-state diagnostic executes successfully and that the vehicle's required wake-up sequence works. A module answering a scan request at one moment does not necessarily validate the entire output circuit. The source provides monitor logic, not a replacement instruction or a method for manually powering sleeping modules.

Source and applicability

This explanation follows the documented GM monitor, not a verified application to every vehicle with this code. Confirm the vehicle, reporting module and calibration in current service information. GM diagnostic table, physical page 1259.