P0674: cylinder 4 glow output open-load monitoring conditions

The documented P0674 monitor checks the cylinder-4 glow output for an open electrical load. It relies on hardware assessment of the circuit connected to the controller.

Preserve the supply context

No glow-system supply fault may be present, battery voltage must be in range and the engine must be running outside cranking. Duty cycle must lie above 2.50% and below 97.50%, with diagnostics enabled. A test conducted while the common supply is faulty cannot establish that this individual-cylinder monitor has passed.

The filter requires ten failures among twenty samples on a 100 ms task. Type B reporting over two trips and glow-lamp indication are listed.

What the resistance statements do and do not mean

The table describes open-load detection at 200 kilohms and no open-load detection below 16 ohms. It does not publish every boundary between those points or identify either as a normal plug resistance specification.

For verification, establish the correct cylinder-4 channel and normal circuit loading during an eligible period. If a service test finds an open path, further isolation must determine where it lies; the code alone does not prove the heating element is the disconnected component. This summary provides no direct-power, removal or drilling procedure. Physical glow-plug service requires the applicable vehicle instructions and suitable equipment.

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 1241.