P037B: A high wait-to-start lamp circuit does not prove excessive glow-plug power

P037B concerns a high condition in the glow/heater indicator control circuit. The cited GM monitor checks the wait-to-start lamp pin for a connection toward a normal or high operating-voltage source. Its subject is the indicator circuit, rather than the current delivered to the engine's glow plugs.

Confirm the lamp circuit is actually being monitored

The configured lamp-present flag and diagnostic enable must both be true. Run/crank supply must be active and above 11 V, while the engine must not be cranking. A lamp observation during starting can therefore occur outside this monitor's stated evaluation window.

The hardware interface performs the electrical test. The table lists a 0.5 Ω reference for the power-short classification and eight failures within ten samples, with a 100-millisecond sampling interval. These are internal monitor facts; they do not identify a test terminal or establish a direct external-power procedure.

Interpret a repeated high result in context

Retain the lamp configuration, supply condition and whether the event occurred outside cranking. A high reading without that context does not establish the same eligible fault the controller reported. A normal lamp appearance also cannot independently prove that the electrical integrity monitor passed.

Further circuit work must distinguish the control connection from unrelated heating circuits using the correct wiring information. The source does not identify the exact failed component, give a universal repair cost or support replacing glow plugs solely because P037B is stored.

Source and applicability

2025 GM 04A documented monitor only. Vehicle, engine and controller calibration applicability must be established separately; no model fitment is inferred from the file. GM PDF, physical page 943.