P037F: glow feedback above the documented 5 V limit

P037F monitors glow-system sense feedback for an excessive value in this GM implementation. The threshold column specifies feedback voltage greater than 5 V.

Scope of the electrical finding

The monitored quantity is the feedback signal, not a direct statement that every glow plug receives more than 5 V. Applying the threshold to a different circuit would misinterpret the page. The strategy describes checking electrical integrity during glow-system operation and mentions an ECU internal fault, but it does not provide a component-isolation test.

The failure filter uses 40 failed samples over 80, with a 50 ms task and Type B reporting over two trips. A single sample above the threshold is not the complete documented reporting rule.

Verify an enabled glow event

The required conditions include key-on engine operation outside cranking, battery voltage in range and an active glow-enable interface. Existing glow-plug electrical faults, glow-system supply faults and diagnostic disable status prevent the stated assessment.

Those gates make two observations useful: whether the glow subsystem was actually enabled, and whether separate supply or plug-circuit faults were present. A test performed while either prerequisite is missing is inconclusive for this code. Use the exact vehicle's service information to identify the feedback circuit and verify its behavior; the table alone does not authorize replacing the ECU or applying external voltage to glow components.

Source and applicability

2025 GM 25OBDG04B diagnostic parameter tables; the cited monitor only. Vehicle, engine and calibration applicability must be confirmed separately. These tables describe detection logic, not a complete repair procedure or a component replacement verdict. gm-2025-04b, PDF page 1179.