Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsStarting System Diagnosis and RepairMedium
A vehicle owner reports that their vehicle starts normally when the engine is cold, but experiences a 'slow crank' or 'no crank' condition when the engine is warm. All battery and charging system tests pass. What is the most likely cause?
- AA faulty neutral safety switch
- BExcessive resistance in the starter motor windings
- CA slipping starter drive (overrunning clutch)
- DA faulty ignition switch
Show answer & explanationAnswer & explanation
Correct answer: B. Excessive resistance in the starter motor windings
When the engine is warm, the resistance of the starter motor windings increases. If the windings already have excessive internal resistance, this increase can push it past the point where the starter can effectively turn the engine, leading to slow cranking or no crank.
Why the other options are wrong
- A. A faulty neutral safety switch would prevent starting regardless of engine temperature.
- C. A slipping starter drive would result in the starter spinning but not engaging the engine, which is not described as a 'slow crank'.
- D. A faulty ignition switch would typically cause starting issues regardless of engine temperature, or intermittent issues unrelated to heat.
Heat-Related Starter Issues
Starting problems (slow crank, no crank) that occur specifically when the engine is warm, often indicating increased electrical resistance in the starter motor or related cables.
- Resistance of conductors increases with temperature.
- Internal starter motor faults (e.g., worn brushes, shorted windings) can be exacerbated by heat.
- Voltage drop tests on main battery cables should also be performed under hot conditions if suspected.
Memory trick: Hot engine, slow turn, check the starter's internal burn.