P02A9: Cylinder 4 leakage detection excludes an electrical injector fault

P02A9 is the cylinder 4 injector-leakage code. In the cited GM implementation, an electrical injector fault is an exclusion condition, which is important when several injector-related codes appear together. The leakage assessment is intended to interpret a different failure pattern.

A qualified mechanical-failure hypothesis

The controller looks for more than 100 misfire counts on cylinder 4 together with a rail-pressure-control minimum error. It describes that combination as evidence for an injection valve failing open. This is a diagnostic hypothesis based on operating results, not a direct visual confirmation of leakage.

The five-second monitor is bounded by engine speed above 1,520 and below 6,000 rpm and relative air charge below 100 percent. Statistical inhibition, general enable conditions and other faults also influence whether it can run.

Keep the fault sequence intact

Record whether the injector electrical diagnosis was clear when P02A9 was evaluated, along with the cylinder 4 counter and rail-control status. An electrical failure that prevents the leakage monitor from running changes the meaning of a later non-returning code.

The same detection pattern is used for other cylinders, but their counters cannot substitute for cylinder 4’s evidence. Confirm engine-specific cylinder numbering before following a service branch. The table’s two-trip classification does not establish a safe operating condition or authorize injector replacement. Verification requires the matching high-pressure fuel-system procedure and suitable equipment.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 706; GM diagnostic table, PDF page 707.