Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsStarting System Diagnosis and RepairMedium
A technician is diagnosing a no-crank condition where the starter motor spins but the engine does not turn over. The battery is fully charged, and the starter solenoid clicks audibly. What is the most probable cause?
- AAn open circuit in the starter motor field windings.
- BA faulty ignition switch.
- CCorroded battery terminals.
- DA faulty overrunning clutch (bendix drive) in the starter motor.
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty overrunning clutch (bendix drive) in the starter motor.
If the starter motor spins but the engine does not turn over, and the solenoid is clicking (indicating it's engaging), the most likely issue is a faulty overrunning clutch (bendix drive). This component is designed to transmit the starter motor's rotation to the flywheel but allow the engine to spin independently once started. If it slips, the motor spins but the engine doesn't crank.
Why the other options are wrong
- A. An open circuit in the field windings would prevent the motor from spinning, which contradicts the symptom 'starter motor spins'.
- B. A faulty ignition switch would prevent the solenoid from clicking or the motor from spinning at all.
- C. Corroded battery terminals would typically cause slow cranking or a no-crank with no or rapid clicking, not a spinning starter motor without engine rotation.
Overrunning Clutch Failure
A failure in the starter motor's overrunning clutch (bendix drive) where the starter motor spins but fails to transmit rotational force to the engine's flywheel.
- Symptom: starter motor spins freely, but engine does not crank.
- Solenoid typically engages and clicks.
- Requires starter motor replacement or overhaul.
Memory trick: Starter spins but engine stands still, the bendix drive lost its will.