I think you'll be surprised at how easy it is to troubleshoot the starter motor to determine if it's good or bad.
In this tutorial, I'll explain the three tests you need to do on the starter to determine if it's good or bad. All three tests are performed without removing the starter motor from the vehicle.
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:
APPLIES TO: This tutorial applies to the following vehicles:
- 2.8L Chevrolet S10 Pickup: 1988, 1989, 1990, 1991, 1992, 1993.
- 2.8L GMC S15 Pickup: 1988, 1989, 1990.
- 2.8L GMC Sonoma: 1991, 1992, 1993.
Important Testing Tips
TIP 1: Ensure the battery has 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
A starter motor that is malfunctioning will cause one of two problems:
- An engine no-crank problem that won't be resolved until the starter is replaced.
- An intermittent engine no-crank problem. In other words, the starter works properly most of the time, but sometimes it doesn't.
NOTE: It's important to remember that if your vehicle has an intermittent engine no-crank issue, the starter motor will need to be checked or tested when the no-cranking issue occurs.
Tools Needed To Test The Starter Motor
No expensive diagnostic equipment is required to test the starter motor. 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 starter motor receives a 12 Volts activation signal when you turn the key to crank and start the engine.
This 12 Volts enable signal is provided to the starter motor solenoid S terminal.
In this second test section, we'll apply 12 Volts directly to the starter solenoid S terminal.
The purpose of this test is to bypass the 12 Volts enable signal from the ignition switch and see if the starter motor will activate and crank the engine.
I recommend that you use a remote start switch to easily and safely apply 12 Volts to the S terminal of the starter motor solenoid. You can purchase or rent this tool at 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 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.