Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsBattery Diagnosis and ServiceHard
A customer repeatedly experiences a 'no-crank' condition, especially when the weather is cold. The technician performs an open-circuit voltage test, which reads 12.6 volts. What is the MOST likely cause of the no-crank condition in this scenario?
- AA faulty starter motor or solenoid.
- BAn excessive parasitic draw.
- CA deeply discharged battery.
- DA shorted cell within the battery.
Show answer & explanationAnswer & explanation
Correct answer: A. A faulty starter motor or solenoid.
An open-circuit voltage (OCV) of 12.6 volts indicates a fully charged battery. If the battery is fully charged but the engine still won't crank, the problem is most likely with the starting system itself, such as a faulty starter motor, solenoid, or associated wiring/relay. A cold weather 'no-crank' can exacerbate a weak starter.
Why the other options are wrong
- B. An excessive parasitic draw would lead to a discharged battery (lower OCV) over time, not a fully charged one with a no-crank.
- C. 12.6 volts indicates a fully charged battery, not a deeply discharged one.
- D. A shorted cell would result in a significantly lower OCV (e.g., ~10.5V for a 12V battery), not 12.6V.
Open-Circuit Voltage Interpretation
Open-circuit voltage (OCV) indicates a battery's state of charge. 12.6V or higher means fully charged. If a fully charged battery cannot crank the engine, the issue lies elsewhere in the starting system.
- 12.6V = 100% charged.
- OCV alone doesn't test cranking ability under load.
- No-crank with high OCV points to starting circuit.
- OCV below 12.4V indicates discharge.
Memory trick: Full Battery, No Crank? Look Beyond the Power Bank!