SPN 653 is the injector for cylinder 3. FMI 5 indicates the ECM detects an open circuit or current below the expected minimum on the injector control circuit when the injector is commanded. Detection typically occurs during injector actuation when the driver current does not rise as expected.

Inspect the injector connector at cylinder 3 for oil intrusion, backed-out pins, or heat damage. Check the under-valve-cover harness and pass-through connector for chafing, pin tension, and oil contamination. Wiggle-test while monitoring current or voltage. Oil leakage into the injector connector is a recurring cause of open-circuit codes.

Injector coil resistance typically 0.3–1.5 Ω depending on platform and injector type — measure cold and compare to other cylinders. Continuity from ECM driver pins to injector connector. Current waveform or peak current during actuation should be present and consistent with sibling cylinders. Open circuit reads infinite resistance.

Repair or replace open wire/harness section $100–300; clean or replace oil-soaked connector $50–150; replace failed injector if coil is open $300–700. Total typical $150–700 depending on whether the injector itself is required and access difficulty.