A technician is diagnosing an intermittent starting issue. When the ignition key is turned to the 'START' position, all dashboard lights dim significantly, but the engine does not crank. The battery has been load tested and is good, and battery cable connections are clean and tight. What is the MOST likely cause of this symptom?
- AA faulty ignition switch.
- BAn open circuit in the starter motor's field windings.
- CExcessive resistance in the starter motor's ground circuit.
- DA faulty starter solenoid control circuit.
Show answer & explanationAnswer & explanation
Correct answer: C. Excessive resistance in the starter motor's ground circuit.
Significant dimming of dashboard lights during a 'no-crank' indicates a very high current draw, but the current is not effectively reaching or turning the starter motor. This points to high resistance in the high-current circuit. Since the battery and positive cable are ruled out, excessive resistance in the starter motor's ground circuit (e.g., corroded ground cable or connection) would cause a large voltage drop on the ground side, preventing the motor from getting sufficient power while still drawing excessive current from the battery, leading to the dimming lights.
Why the other options are wrong
- A. A faulty ignition switch would prevent the starter from engaging at all, without necessarily causing extreme dimming.
- B. An open circuit in the field windings would drastically reduce current draw, not cause significant dimming.
- D. A faulty control circuit would prevent the solenoid from engaging, leading to no click and no dimming, or minimal dimming if only the control circuit drew power.
High Current Draw, No Crank Diagnosis
Diagnosing a 'no-crank' condition accompanied by significant voltage drop (dimming lights) across the electrical system, indicating an excessive current draw without effective power delivery to the starter motor.
- Signifies a high-resistance fault in the high-current starter circuit.
- Common causes: corroded battery cables (positive or ground), faulty starter motor (shorted windings, seized), or worn starter solenoid contacts.
- Requires voltage drop testing on both positive and ground sides of the starter circuit.
Memory trick: Dim lights, no crank, big current, ground's the tank.