Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsStarting System Diagnosis and RepairEasy
A technician is diagnosing a no-crank, no-click condition on a vehicle. The battery is fully charged and tests good. When the key is turned to the 'START' position, the technician measures 12.6 volts at the starter motor's main power terminal and 0 volts at the starter solenoid's S-terminal. What is the most likely cause of this condition?
- AAn open circuit in the starter control (S-terminal) wire
- BA short circuit in the starter motor windings
- CA faulty starter motor
- DA discharged battery
Show answer & explanationAnswer & explanation
Correct answer: A. An open circuit in the starter control (S-terminal) wire
No voltage at the S-terminal indicates that the starter solenoid is not receiving the signal to engage, despite the battery being good. An open circuit in this wire would prevent the signal from reaching the solenoid.
Why the other options are wrong
- B. A short circuit in the starter motor windings would likely draw excessive current, but the S-terminal would still receive voltage.
- C. A faulty starter motor would typically still receive voltage at the S-terminal and may click, but not crank.
- D. The problem states the battery is fully charged and tests good, eliminating this as a cause.
S-terminal Voltage Test
Measuring voltage at the starter solenoid's S-terminal (control terminal) to confirm if the starter is receiving the command signal from the ignition switch or starter relay.
- 0 volts indicates no command signal is reaching the solenoid.
- Battery voltage indicates the command signal is present.
- Used to differentiate between control circuit issues and starter motor/solenoid issues.
Memory trick: Key turns, no power, no sound, check the S-terminal wire now!