To test a car starter, you need to perform a systematic diagnosis focusing on electrical signals and mechanical function. The starter motor is an electric motor that cranks the engine to begin combustion. A faulty starter will often result in a single loud click when you turn the key, with no engine cranking. The most reliable method involves using a multimeter to check for power and voltage drop tests to identify bad connections.
First, ensure the battery is fully charged. A weak battery is the most common cause of starting problems. Perform a voltage test; a healthy battery should show 12.6 volts when the car is off.
Next, conduct a starter voltage test. Have an assistant turn the ignition key to the "start" position while you probe the starter's main power terminal (the large cable from the battery). You should see battery voltage (around 12V). If there's no voltage, the issue is likely a faulty starter relay, ignition switch, or a broken wire.
If power is present but the starter doesn't engage, perform a voltage drop test. This identifies high resistance in the circuit. With the key in "start," measure the voltage between the battery's positive post and the starter's main terminal. A reading above 0.5 volts indicates excessive resistance in the cable or connections. Clean the terminals and retest.
You can also test the starter solenoid's control circuit. The small wire (typically an "S" terminal) should receive a 12V signal when the key is turned. If it does, but the starter doesn't activate, the solenoid is likely faulty. If the starter motor spins but doesn't engage the engine flywheel, the issue is a faulty solenoid or a damaged starter drive (Bendix gear). For a definitive test, a bench test at an auto parts store can verify the starter's internal mechanical and electrical health.
| Diagnostic Test | Expected Reading | Indicates a Problem If... |
|---|
| Battery Voltage (static) | 12.6V or higher | Below 12.4V |
| Starter Power Terminal Test | ~12V when cranking | No voltage present |
| Control Circuit ("S" Terminal) Test | ~12V when cranking | No voltage present |
| Positive Cable Voltage Drop | Less than 0.5V | Above 0.5V |
| Ground Cable Voltage Drop | Less than 0.5V | Above 0.5V |
