P067B: cylinder 4 glow-plug high-circuit detection

P067B is an electrical-integrity fault for the cylinder 4 glow-plug output. In the 2025 GM table reviewed here, “high” means the controller detects a connection toward a voltage source. It does not describe excessive combustion temperature or prove that the glow plug itself is defective.

Why load resistance matters

The monitor uses two power-short detection limits. With load resistance above 0.65 ohm, the external connection must have impedance below 0.5 ohm to the relevant voltage source. With load resistance between 0.2 and 0.65 ohm, that impedance limit becomes 0.14 ohm. These are controller detection criteria, not a universal resistance specification for testing a removed glow plug.

This distinction matters when interpreting a resistance measurement: a single number cannot reproduce the monitor without knowing the load regime and the path being measured.

Conditions and confirmation

The diagnostic requires calibration enablement, acceptable battery voltage, an active diagnostic system, and no glow-system supply fault. It operates with the key on and engine running, excluding cranking. The table specifies 10 failing samples within 20 samples at a 100-millisecond task rate, with Type B, two-trip reporting and glow-lamp activation.

A test performed only during cranking therefore does not confirm this monitor's operating result. Review whether its enabling conditions were met and whether the high-circuit fault returns on cylinder 4 before attributing the problem to that plug. This explanation covers the documented monitor only; model and engine applicability and the circuit isolation procedure require vehicle-specific service information.

Source: GM monitor, PDF page 1245.