ASE A1 Engine RepairEngine Electrical Systems (General)Medium
A technician is performing a starting system voltage drop test on the negative side of the circuit. A multimeter is connected with the positive lead to the battery negative post and the negative lead to the engine block. During cranking, the meter reads 0.8 volts. What does this reading indicate?
- AThe starter motor is drawing too much current.
- BThe battery is severely undercharged.
- CThe reading is within normal operating specifications.
- DThere is excessive resistance in the negative battery cable or engine ground.
Show answer & explanationAnswer & explanation
Correct answer: D. There is excessive resistance in the negative battery cable or engine ground.
A voltage drop of 0.8 volts on the negative side (battery negative to engine block) during cranking is excessive. The maximum acceptable voltage drop for this circuit is typically 0.2-0.3 volts. This indicates high resistance in the negative battery cable or the engine ground connection, impeding current flow and potentially causing slow cranking.
Why the other options are wrong
- A. Excessive current draw by the starter motor would show up as a high voltage drop on the positive side or a significantly reduced battery voltage, but this test specifically targets the negative circuit's resistance.
- B. While an undercharged battery could cause slow cranking, the voltage drop test specifically points to resistance in the ground circuit, not the battery's state of charge.
- C. A normal voltage drop for the negative battery cable/engine ground circuit should be much lower, typically below 0.3 volts. 0.8 volts is well outside normal specifications.
Negative Side Voltage Drop
Negative side voltage drop testing measures the resistance in the ground path from the battery negative terminal to the engine block or chassis, ensuring a low-resistance return path for current.
- Evaluates the integrity of ground connections.
- Excessive drop indicates poor ground or cable resistance.
- Typical maximum drop is 0.2-0.3V during cranking.
Memory trick: Negative drop is high? 'Ground' your suspicion or the current will fly!