P066D: load-dependent high-voltage fault on glow circuit 2

P066D is the cylinder-2 glow output's short-to-power diagnosis in the cited table. Its hardware fault specification depends on how much load resistance is connected to the output.

Why one resistance number is insufficient

For load above 0.65 ohm, a path below 0.5 ohm toward a normal or high supply-voltage source meets the stated power-short case. For load between 0.2 and 0.65 ohm, the corresponding path criterion is below 0.14 ohm.

Those paired conditions characterize detection, not the resistance a good replacement plug must measure. Using one of the short-path values as a blanket plug specification would confuse the fault path with the load itself.

Assess valid operation

The table enables the check during engine operation outside cranking with battery voltage in range, no glow-system supply fault and diagnostics active. Its filter is ten failed samples among twenty at 100 ms intervals, with Type B reporting and glow-lamp indication.

A useful verification confirms the correct cylinder channel and normal electrical behavior during an eligible period. A reading obtained during a separate supply fault does not establish that this monitor ran. The source cannot isolate wiring, the connected load and control electronics by code alone. Follow the exact service procedure rather than applying external power or inferring a need for immediate plug replacement.

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 1235.