All of the tests you're about to read are pretty much the standard way starter motors are tested on the car or truck in an auto repair shop. You'll be surprised just how easy they are. Not to mention the money you'll be saving by doing it yourself.
If you've already read the important tips on testing the starter on the previous page, we can now start. I'll be using a photo of a typical starter motor just for ease of explaining the tests. The starter motor on your vehicle will look similar.
Also, even tho' all of the photos show the starter motor off of the car, this is an ON-CAR Test of the starter motor.
Starter Motor Circuit Descriptions
Below are the descriptions of the main circuits that will be tested on this on car starter test:
- Number 1: This is where the battery positive cable from the battery is attached to.
- Number 2: This is the S terminal of the starter solenoid. This is where the START/CRANK wire is attached to and the one that delivers the 12 Volts from the ignition switch when you turn the key to START.
- Some vehicles will use a nut to attach this circuit to the starter solenoid.
- Other vehicles (mainly Japanese cars & trucks) will have a female spade terminal instead that mates to a male spade terminal.
- Number 3: The grounding point. The starter motor is grounded thru' its case.
Start With The Battery First
The battery's condition is the most important part of the starter tests and the first thing that has to be checked.
There are two parts to this test. Visually checking that the battery terminals for obvious problems and testing the battery's voltage with a multimeter.
- Eye-balling the battery:
- The battery terminals should not be full of corrosion (like in the photo).
- The battery terminals should not be loose or broken.
- If these conditions are present, then clean or replace the battery terminals.
- Battery voltage test:
- With a digital multimeter or an analog multimeter test the battery's voltage.
- A good working battery will show 12.6 Volts. The bare minimum will be 12.3 Volts.
- Any battery voltage below 12.3 Volts, and you'll need to charge the battery first, or use a battery jump box during the tests, or replace it with a known-good battery.
- Having a good working battery is important to test the starter on the vehicle.
After cleaning, or repairing the battery terminals, or replacing a BAD battery, or charging a discharged battery the car or truck may start. If this is the case, well good for you. Further testing is not required.
TEST 1: Testing The START Signal From The Ignition Switch
As mentioned before, the circuit labeled by the number 2 in the photo is commonly known as the S terminal of the starter solenoid. Attached to this S terminal is the wire that comes from the ignition switch via the neutral safety switch. This is a 12 Volt signal.
When the key is turned to crank the engine, juice flows from the ignition switch, thru' the neutral safety switch and onto the S terminal of the starter solenoid.
On a good and working starter motor, as soon as this 12 Volt signal is received, the starter motor comes alive and cranks the engine.
This test verifies the presence of these 12 Volts and indirectly tests the ignition switch and the neutral safety switch. You'll only get one of two results from this test: you'll either get 12 Volts or not. Let's get started:
Raise and support the vehicle on jack stands (if applicable).
The starter motor must remain connected to all of its cables/wires.
Attach the BLACK multimeter lead (with an appropriate tool) to the negative terminal of the battery.
With a wire-piercing probe or a suitable tool, pierce the wire that is attached to the S terminal of the starter solenoid. This terminal is labeled with the number 2 in the photo above.
Or if you have enough room, touch the S terminal with the multimeter lead.
Put the multimeter in Volts DC mode. Have an assistant turn the key to the START position and have him or her hold it there while you observe the multimeter's voltage reading.
Your multimeter should register 10 to 12 Volts DC as your helper turned the key to crank the engine.
Let's take a look at what your multimeter test result means:
CASE 1: The multimeter DID NOT register any voltage. Then the starter motor is not the cause of the ‘does not crank’ condition. Without these 12 Volts here (when the key is turned to the START position) the starter motor will not come out to play. Possible causes for this missing voltage are:
- Bad ignition switch.
- Bad neutral safety switch.
Your next step is to go to: TEST 2: Adding 12 Volts To The S Terminal Circuit.
CASE 1: The multimeter DID register 10 to 12 Volts. Then the START signal is being received. The presence of this voltage confirms that:
- The ignition switch is good.
- The neutral safety switch is good.
The next step is to make sure the starter motor is getting plenty of batter power. For this test, go to: TEST 3: Voltage Drop Testing The Power Circuit.