P0673: cylinder 3 glow circuit appears electrically unloaded

P0673 is an open-load check of cylinder 3's glow-plug circuit in this source. The hardware monitor judges the electrical load connected to the controller output during operation.

Electrical loading is not a direct heat test

The source's 200-kilohm detection condition and below-16-ohm nondetection statement describe the open-circuit monitor. They do not establish how rapidly a healthy plug heats or provide a complete resistance-versus-temperature specification.

A circuit can therefore require further assessment even after its load is recognized, while an open-load result still does not pinpoint the disconnected element. Keep those distinct questions separate when reviewing the code.

Verify within the duty window

The check requires duty cycle above 2.50% and below 97.50%, valid battery voltage, no glow-system supply fault and engine running outside cranking. Diagnostics must be enabled. Ten failures among twenty samples at 100 ms intervals meet the documented filter, with Type B reporting and glow-lamp indication.

A test at an excluded duty-cycle extreme does not reproduce this monitoring condition. Verification should confirm valid cylinder-3 loading with the correct prerequisites, using the vehicle's service procedure to distinguish the plug from its connections and controller circuit. The table supplies no pinout, replacement command or permission to apply uncontrolled battery power to the glow element.

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 1240.