Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisHard
A technician is diagnosing an intermittent starting issue. The starter motor occasionally fails to crank, but all dashboard lights illuminate brightly. A voltage drop test on the starter motor's main positive cable (from battery to starter) shows 0.1V during a successful crank. When the no-crank condition occurs, the technician measures 12V at the starter solenoid's S-terminal (control wire). What is the MOST likely cause?
- AA discharged battery.
- BA faulty starter solenoid or starter motor.
- CA poor ground connection for the starter motor.
- DExcessive resistance in the starter motor's main positive cable.
Show answer & explanationAnswer & explanation
Correct answer: B. A faulty starter solenoid or starter motor.
If the battery is good (bright lights), the main positive cable shows low voltage drop (0.1V is excellent), and the solenoid's S-terminal receives 12V (indicating the control circuit is working), but the starter still doesn't crank, then the fault must be within the starter assembly itself. This points to either a faulty starter solenoid (not engaging or passing high current) or an internal issue with the starter motor.
Why the other options are wrong
- A. Bright dashboard lights indicate a charged battery, ruling this out.
- C. A poor ground would cause a high voltage drop on the ground side, which wasn't tested, but the other tests rule out primary power issues.
- D. A 0.1V drop on the main positive cable is excellent, ruling out excessive resistance here.
Starter No-Crank Diagnosis
When a starter fails to crank despite proper battery voltage and control signal to the solenoid, the fault is typically within the starter motor assembly itself (solenoid or motor).
- Verify battery voltage first.
- Confirm solenoid control signal (S-terminal voltage).
- Check main power cable voltage drop.
- If all external inputs are good, diagnose starter assembly.
Memory trick: Battery's good, control's on, if it won't crank, starter's gone.