During a starting current draw test, a technician measures 350 amps with the engine cranking at 150 RPM. The manufacturer's specification for this engine is 180-250 amps at 200 RPM. The battery is fully charged and tests good. What does this measurement most likely indicate?
- AExcessive resistance in the starter motor.
- BA short circuit in the starter motor windings or engine mechanical drag.
- CInsufficient battery capacity.
- DA normal starter motor current draw for this application.
Show answer & explanationAnswer & explanation
Correct answer: B. A short circuit in the starter motor windings or engine mechanical drag.
A current draw of 350 amps is significantly higher than the specified 180-250 amps, especially when cranking at a lower than specified RPM (150 RPM vs 200 RPM). High current draw with slow cranking points to either a short circuit within the starter motor windings (e.g., shorted armature or field coils) or excessive mechanical drag on the engine (e.g., seized engine, internal engine problem). Since the battery is good, it's not a supply issue.
Why the other options are wrong
- A. Excessive resistance in the starter motor would cause a LOWER current draw and slow cranking, not a higher one.
- C. Insufficient battery capacity would result in a lower current delivery and weaker cranking, not an excessively high current draw.
- D. 350 amps is well above the specified range of 180-250 amps, indicating an abnormal condition.
High Starter Current Draw Diagnosis
Diagnosing a condition where the starter motor draws significantly more current than specified, often accompanied by slow cranking, indicating either an internal starter fault or excessive engine mechanical resistance.
- Measured with an inductive amp clamp around the main battery cable.
- High current draw + slow/no crank = shorted starter windings or engine mechanical issue.
- High current draw + normal/fast crank = unlikely, usually means the starter is working hard but efficiently.
Memory trick: Current too high, engine too low, a short or drag is where to go.