P067C: cylinder 5 glow-plug low circuit and inrush faults

The documented GM implementation of P067C monitors the cylinder 5 glow-plug circuit for a low-side electrical condition. Its definition includes both a ground-short detection path and an excessive-inrush-current path. Consequently, finding the code does not establish that a permanent short to ground is present.

Two ways to fail

The hardware criteria list a ground-short detection impedance of 0.11 ohm and state that a ground short should not be detected above a circuit impedance of 0.19 ohm. The table also allows the fault when the initial current profile exceeds its specified envelope. That inrush check occurs at key-on, once per driving cycle; the actual profile is not reproduced on this page.

A normal measurement after the initial activation can therefore miss the event responsible for the stored code. Conversely, the listed impedances should not be treated as a complete resistance-test procedure for an unpowered plug.

What a valid retest needs

For the operating check, GM lists engine running with cranking excluded, battery voltage in range, no glow-system supply fault, and duty cycle above 2.5% but below 97.5%. The diagnostic must also be enabled. Its failure counter requires 10 samples in a 20-sample window with 100-millisecond updates; reporting is Type B over two trips.

Separate the startup inrush event from the running electrical check when reviewing captured data. A sustained running test alone does not repeat the once-per-cycle branch. The source establishes monitor behavior, not a replacement recommendation or confirmed model coverage; use the applicable vehicle procedure for isolation.

Source: GM monitor, PDF page 1246.