Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A technician is diagnosing a vehicle that intermittently fails to start. When the ignition key is turned to the 'START' position, the technician observes that the starter motor does not engage, and there is no click from the starter solenoid. Further testing reveals that the battery voltage is 12.6V, and the voltage at the starter solenoid's S-terminal (control wire) is 12.0V when the key is in the 'START' position. What is the MOST likely cause of this condition?
- AA discharged battery
- BA faulty ignition switch supplying insufficient current
- CAn open circuit in the starter motor's main power feed
- DWorn or pitted starter solenoid contacts
Show answer & explanationAnswer & explanation
Correct answer: D. Worn or pitted starter solenoid contacts
If the battery voltage is good (12.6V) and the solenoid is receiving proper control voltage (12.0V) when the key is turned, but the starter does not engage and the solenoid does not click, it indicates an internal failure of the solenoid. Worn or pitted contacts within the solenoid are a common cause for this symptom, preventing the high current flow to the starter motor windings.
Why the other options are wrong
- A. The battery voltage of 12.6V indicates a fully charged battery, so a discharged battery is not the issue.
- B. The 12.0V at the S-terminal indicates the ignition switch is supplying sufficient voltage to activate the solenoid, ruling out an insufficient current issue from the switch itself.
- C. An open circuit in the starter motor's main power feed would prevent the starter from cranking, but the solenoid would still click if it were receiving control voltage and attempting to engage.
Starter Solenoid Failure
A starter solenoid can fail internally, preventing the starter motor from engaging, even when it receives the correct control voltage from the ignition switch.
- Commonly caused by worn or pitted internal contacts.
- Symptoms include no starter motor engagement and no solenoid click.
- Requires solenoid or starter motor replacement.
Memory trick: Key turns, power flows, but the solenoid's silent show.