Automotive Service Excellence (ASE) A8 Engine PerformanceIgnition System Diagnosis and RepairHard
A technician is performing a diagnostic check on a vehicle experiencing a no-start condition. Using a spark tester, they confirm that there is no spark from any of the ignition coils. A scan tool shows no communication with the Engine Control Module (ECM). All fuses related to the ECM and ignition system are checked and found to be good. What should the technician check NEXT to diagnose the no-start condition?
- AThe fuel pump relay operation.
- BPower and ground supply to the ECM.
- CThe resistance of the crank position sensor.
- DThe exhaust system for blockages.
Show answer & explanationAnswer & explanation
Correct answer: B. Power and ground supply to the ECM.
If there's no spark and no communication with the ECM, the primary suspect is a non-functioning ECM. Before condemning the ECM, it's crucial to verify that it's receiving both power and ground. Without proper power and ground, the ECM cannot operate, communicate, or command spark.
Why the other options are wrong
- A. The fuel pump relay is related to fuel delivery, not directly to spark or ECM communication.
- C. While a faulty crank sensor can cause no spark, if the ECM isn't communicating, it's a more fundamental issue than a sensor input.
- D. An exhaust blockage would cause a no-start or poor running but wouldn't prevent ECM communication or spark output directly.
ECM Power/Ground Check
A diagnostic step to verify that the Engine Control Module (ECM) is receiving proper electrical power and ground connections when symptoms indicate a non-functional or non-communicating ECM.
- Essential for ECM operation and communication.
- Check before condemning ECM.
- Use wiring diagrams to locate correct terminals.
Memory trick: No spark, no comm? Check ECM's home (power/ground).