Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsStarting System Diagnosis and RepairMedium
A technician observes that when the ignition key is turned to the 'START' position, the starter motor spins freely and quickly, but the engine does not crank. What is the most likely cause?
- AExcessive resistance in the main positive battery cable.
- BA faulty ignition switch.
- CA seized engine.
- DA faulty starter drive (overrunning clutch).
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty starter drive (overrunning clutch).
If the starter motor spins freely and quickly but doesn't engage the engine, it indicates that the starter motor itself is receiving power and operating, but the mechanism that connects its rotation to the engine (the starter drive or overrunning clutch) is failing to engage or is slipping.
Why the other options are wrong
- A. Excessive resistance in the main positive cable would cause the starter to spin slowly or not at all, not freely and quickly.
- B. A faulty ignition switch would prevent the starter from spinning at all or cause intermittent issues.
- C. A seized engine would cause the starter motor to either not spin at all (no-crank, click) or spin very slowly, drawing excessive current, not spin freely and quickly.
Overrunning Clutch Failure
A malfunction of the starter drive's overrunning clutch, causing the starter motor to spin without engaging or transmitting torque to the engine's flywheel, resulting in a 'starter spins, no crank' condition.
- Symptoms include a whirring sound from the starter without the engine turning.
- The clutch is designed to disengage the pinion from the flywheel once the engine starts, preventing overspeeding.
- Failure means the pinion either doesn't engage or slips when engaged.
Memory trick: Starter spins fast, engine stands still, the clutch has lost its will.