Battery and Starting System Diagnosis and Repair
Battery Fundamentals
Candidates must know battery construction, ratings (CCA, reserve capacity, amp-hour), and state-of-charge versus state-of-health. A battery can show 12.6 V at rest and still fail a load test-voltage alone does not prove capacity. Understand that surface charge must be removed (headlights on briefly or a load applied) before an accurate open-circuit voltage reading. Know the correct charging procedure and that a deeply discharged battery may need a slow charge to recover.
Testing the Battery
Be able to describe a conductance/capacitance tester and a load test (typically half the CCA rating for 15 seconds, watching for voltage to stay above about 9.6 V at room temperature). Recognize that temperature affects results and that a battery must be at least 12.4 V before load testing.
Starting System Diagnosis
Understand the starter control circuit: ignition switch, neutral safety or clutch switch, starter relay, and solenoid. Know the difference between a no-crank, slow-crank, and crank-no-start complaint and how each narrows the fault. Test the control circuit for voltage at the solenoid S terminal and the high-current path with voltage drop. A clicking solenoid with no crank often indicates low battery, bad connections, or a faulty solenoid, not necessarily a bad starter.
Traps and Rule of Thumb
Questions confuse the solenoid's two jobs-pulling the drive into mesh and closing the high-current contacts. A solenoid that clicks but does not crank may have good control voltage but burned contacts. Rule of thumb: before condemning a starter, verify battery state of charge, perform voltage drop on both the positive and ground sides, and confirm control voltage at the solenoid.