P1318 — IG. COIL 3 - LOW OUTPUT

Diagnostic algorithm

1. Retrieve DTCs and freeze frame; note engine conditions (RPM, load, temp) when fault occurred.
2. Check battery voltage and charging system; ensure good battery connections. Low system voltage can reduce coil output.
3. Visually inspect ignition coil 3 and harness for damage, oil contamination, loose or corroded terminals. Repair as needed.
4. With ignition OFF disconnect coil 3 connector and check for continuity to ECM pins and to ground; check for shorts to power/ground.
5. Measure coil 3 primary and secondary resistances and compare to factory specs. If out-of-spec, replace coil.
6. Swap coil 3 with another cylinder's coil (if coils are identical). Clear codes and run engine. If misfire/code moves to swapped cylinder, replace the coil.
7. If coil tests OK, backprobe coil primary with a DVOM or oscilloscope while cranking/running to verify proper pulse, voltage, and current. Check dwell/pulse width and amplitude.
8. If no primary pulse or weak pulse from ECM, inspect driver supply fuses/relays and wiring to ECM. Check ECM ground connections.
9. If wiring and coils are good but no proper driver signal, suspect faulty ignition driver in ECM — verify with manufacturer procedures before ECM replacement.
10. After repair, clear codes and road-test under conditions similar to freeze-frame; re-scan to confirm the fault is cleared.