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Comprehensive Guide to Checking Your Car’s Charging System

February 14, 2024

Maintaining the charging system is vital for any vehicle’s reliability. This streamlined guide covers the essential steps for a thorough evaluation.


Required Tools:

  • Multimeter with DC voltage, min/max, and AC modes
  • Alligator clips

Battery Voltage Check:

  1. Switch the multimeter to DC voltage mode.
  2. Attach the red lead to the positive terminal and the black lead to the negative terminal of the battery.
  3. A 12.6V reading signifies full charge; below 12.4V requires recharging.

Starter Motor Voltage Drop Test:

  1. Activate the min/max feature on the multimeter.
  2. During engine cranking, the voltage should not fall below 9.7V.

Charging Voltage Test:

  1. Start the engine and turn on high-demand electrical components (e.g., blower, headlights).
  2. Increase the engine speed to 1500-2000 RPM. The charging voltage should not surpass 15.5V.
  3. Normal charging voltage is 13.5-14.5v.

Alternator Diode Test:

  1. Change the multimeter to AC mode.
  2. At idle, AC voltage should remain under 0.5V, indicating functional diodes.

Parasitic Draw Test:

  1. Adjust the multimeter to Amp DC mode for current measurement.
  2. Make sure to swap the leads on your multimeter to COM and A (for Amps).
  3. Disconnect the vehicle’s negative battery cable. Connect the multimeter’s negative lead to the negative battery post and the positive lead to the negative cable. This creates a series circuit through which any current draw by the vehicle’s electrical system will pass, allowing the multimeter to measure it.
  4. A reading under 25 milliamps suggests no significant parasitic draw.

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