This tutorial is a step-by-step guide to testing the starter motor to see if it's good or bad.
All four tests are performed without removing the starter motor from the vehicle and do not require expensive diagnostic tools.
NOTE: The starter motor test in this tutorial is an on-car test. The photos I'm using show the starter motor off of the vehicle only to explain the test connections better.
Contents of this tutorial:
- Important Testing Tips.
- Symptoms Of A Bad Starter Motor.
- Tools Needed To Test The Starter Motor.
- TEST 1: Applying 12 Volts To The S Terminal.
- TEST 2: Verifying The 12 Volt Start Signal.
- TEST 3: Voltage Drop Testing The Battery (+) Cable.
- More 2.5L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Motor De Arranque (1987-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.5L Chevrolet S10 Pickup: 1987, 1988, 1989, 1990, 1991, 1992, 1993.
- 2.5L GMC S15 Pickup: 1987, 1988, 1989, 1990.
- 2.5L GMC Sonoma: 1991, 1992, 1993.
Important Testing Tips
TIP 1: The battery must have a full charge before starting any of the tests in this tutorial.
TIP 2: The battery cable terminals and the battery posts should be clean and corrosion-free before starting the tests.
TIP 3: Read the entire article first to familiarize yourself with the tests.
TIP 4: Use jack stands for safety. Don't trust the jack alone to keep your vehicle up in the air while you're underneath it!
TIP 5: Take all necessary safety precautions. Use safety glasses while working underneath the vehicle. Be alert and think safety all of the time.
Symptoms Of A Bad Starter Motor
In my many years of experience (as an automotive technician), I've noticed that a starter motor typically fails in two ways:
- The starter motor fails and no longer cranks the engine.
- The starter motor fails intermittently. In other words, the starter motor works most of the time, but sometimes doesn't
NOTE: If the starter motor is failing intermittently, you must test it when it isn't cranking the engine.
Tools Needed To Test The Starter Motor
The starter motor test doesn't require any expensive diagnostic equipment. Here's a list of the things you'll need:
- A jack.
- You'll need to raise your vehicle to access to the starter motor.
- Jack stands.
- A remote starter switch.
- If you'd like to see what a remote starter switch looks like, you can follow this link: Actron CP7853 Remote Starter Switch For 6V And 12V Automotive Starting Systems
- You can either buy this tool online, or you can buy it at your local auto parts store (AutoZone, O'Reilly Auto Parts, Pepboys, etc.).
- A multimeter or a 12 Volt automotive test light.
- If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
- A wire piercing probe.
- This tool is not an 'absolute must-have tool,' but I can tell you from experience that it makes it a whole lot easier to probe the S terminal wire for the Start Signal.
- If you'd like to see what this tool looks like, you can find out more about it here: Wire Piercing Probe Tool Review (Power Probe PWPPPPP01).
- A helper.
TEST 1: Applying 12 Volts To The S Terminal
The first thing we'll do to determine if the starter motor is good or bad is to apply 12 Volts directly to the S terminal of the starter motor solenoid.
If the starter motor is working properly, applying 12 Volts directly to the S terminal will activate the starter motor.
If the starter motor is defective, applying 12 Volts to the S terminal will have no effect on the starter motor.
The easiest and safest way to apply 12 Volts to the S terminal is with a remote start switch, which you can purchase or borrow from your local AutoZone or O'Reilly Auto Parts store.
You can see an example of a remote start switch and where to buy it here:
IMPORTANT: Remove the key from the ignition switch for this test. If your Chevy S10 (GMC S15 pickup, GMC Sonoma) is equipped with a standard transmission, place it in neutral.
OK, let's get testing:
Raise the front of your vehicle and place it on it's jack stands (to gain access to the starter motor).
Disconnect the battery negative (-) terminal.
You'll reconnect it back in one of the following steps; for now, it's a safety precaution as you set up the test.
Attach one end of the remote starter switch to the battery positive (+) post.
Attach the other end of the remote starter switch to the S terminal of the starter motor solenoid.
This is easier said than done, so take your time and make sure the connection is on the S terminal of the starter motor solenoid.
Also, in case you're wondering, you can leave the starter motor solenoid's S terminal wire connected to the engine's wiring harness connector or not, the test will work either way.
Reconnect the battery negative (-) cable to the battery negative post.
Apply 12 Volts to the S terminal wire of the starter motor starter solenoid with your remote starter switch.
You'll get one of two results:
1.) The starter will activate and will turn over the engine.
2.) The starter motor won't do a thing.
Let's see what your test results mean:
CASE 1: The starter motor cranked the engine. This is the correct and expected test result and confirms the starter motor itself is functioning correctly.
Since the starter motor isn't cranking the engine when you turn the key to crank it, the next step is checking it's receiving an activation signal. Go to: TEST 2: Verifying The 12 Volt Start Signal.
CASE 2: The starter motor DID NOT crank the engine. This test result usually tells you that the starter motor is bad and needs replacement.
Before replacing the starter motor, your next step is ensuring that the cable connecting the starter motor to the battery positive (+) terminal is OK. Go to: TEST 3: Voltage Drop Testing The Battery Cable.