P050D: Incomplete combustion during the cold-start dual-pulse strategy

P050D is a cold-start rough-idle diagnostic. The cited GM strategy evaluates combustion quality while cold-start emissions reduction and dual-pulse injection are active. It counts engine cycles with incomplete combustion relative to the total qualifying dual-pulse cycles.

The observation window is narrow

The strategy requires the misfire algorithm to be enabled, catalyst temperature below 550°C, coolant above −12°C and no higher than 66°C, and barometric pressure at least 70 kPa. The initial dual-pulse conditions include runtime below twenty seconds. The test ends when dual pulse stops or the first 500 engine cycles have been reached.

Consequently, smooth warm idle is weak evidence against a fault that occurs only during this early strategy. Repeated hot restarts may never recreate the relevant window.

Use cold-start data and enabling status

The controller derives incomplete-combustion evidence from crankshaft deceleration thresholds shared with misfire monitoring. Those thresholds depend on speed/load and the specific vehicle calibration; the page does not support a universal roughness or misfire-count limit.

Preserve startup temperature, injection strategy state and cylinder/event information before clearing codes. Injector, fuel-pressure, ignition, crankshaft and other input faults can prevent this monitor from running.

Verification should include an appropriate cold-start opportunity with the emissions strategy active and a completed test. P050D alone does not identify an injector, ignition part or mechanical defect. Its value is locating the combustion problem in a specific controlled startup phase.

Source and applicability

This explanation is limited to the 2025 GM 25OBDG03A monitor on page 321, page 322, page 323, page 324. Its thresholds are calibration examples, not universal specifications. Confirm the vehicle, engine and controller procedure before applying them.