P06C7: cylinder 3 glow-plug performance judged by resistance

The reviewed GM P06C7 row calls the test a cylinder 3 electrical-resistance rationality check. The generic “glow plug incorrect” wording is broader than the actual evidence: the controller has judged calculated operating resistance to be outside its permitted range.

Measurement and qualification

Resistance is derived from the ratio of measured voltage to measured current. GM prints an allowed parameter window of 0.23 to 2.00, but this page does not explicitly attach a unit to the expression. The values are useful for understanding the controller's comparison; they are not a substitute for the vehicle's component-test specification.

The monitor waits until the plug has been commanded on for a calibrated time. It also requires no individual plug electrical fault and no glow-plug voltage-feedback fault. These prerequisites mean that a simple electrical failure may stop the performance calculation from being evaluated. Absence of a new P06C7 while such a prerequisite fault exists is therefore weak evidence of recovery.

What should be verified

Battery voltage must be acceptable, diagnostics enabled, and the engine running with cranking excluded. The failure logic counts 15 samples out of 25 at a 100-millisecond update interval; the listed lamp class is Type B over two trips.

A meaningful confirmation checks that the commanded-on interval and prerequisite checks were completed, then reviews cylinder 3's rationality result. Neither the code title nor this table establishes that a replacement glow plug is required. These calibration facts apply only to the documented monitor until the vehicle's model and engine application are verified.

Source: GM monitor, PDF page 1252.