TEST 2: Verifying The 12 Volt Start Signal
As stated in TEST 1, when you turn the key to crank and start the engine, the starter motor receives a 12 Volts activation signal.
Now your next step, and the focus of this test section, is to verify that the activation signal is present in the wire connected to the S terminal when your helper turns the key to the START position.
You'll verify the presence of the activation signal with a multimeter voltage test.
NOTE: You can perform this test with the 'S' wire connected or disconnected to the 'S' terminal.
These are the test steps:
Raise and place the front of the vehicle on jack stands (if it isn't already).
Place your multimeter in Volts DC mode.
Ground the black multimeter test lead directly on the negative (-) battery terminal using a jump start cable.
You can also Ground it on the engine, if you can find a clean, unpainted and rust-free spot of metal.
Connect the red multimeter test lead to the 'S' terminal wire using an appropriate tool.
Don't know which wire is the 'S' terminal wire? This is the one that connects to the smaller of the three studs on the starter motor solenoid.
The 'S' terminal wire (circuit) is the one that delivers the Start (Crank) signal from the ignition switch.
Have your helper turn the key to crank the engine when the test is setup.
Your multimeter should read 10 to 12 Volts DC.
OK, let's see what your test results mean:
CASE 1: Your multimeter registered 10 to 12 Volts. This is the correct and expected test result and it confirms that the starter motor is receiving its activation signal.
Now, in most cases, you could stop here and replace the starter motor and be done. But, I suggest one more test so that you can be absolutely sure there isn't another issue to deal with.
Your next test is to voltage drop test the battery positive (+) cable. This is a very easy and simple test to do. Go to: TEST 3: Voltage Drop Testing The Battery (+) Cable.
CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This test result lets you know that the starter motor isn't receiving an activation signal.
Although finding out why this activation signal is missing is beyond the scope of this tutorial, the most likely causes are:
- A bad starter motor relay.
- A bad park-neutral safety switch.
- A bad clutch pedal switch.
- A bad ignition switch.
- An anti-theft system fault (if equipped).
TEST 3: Voltage Drop Testing The Battery (+) Cable
As you already know, the starter motor draws all the current to crank the engine from the battery.
The wire that supplies this power to the starter motor is the heavy gauge cable that attaches to the BAT terminal of the starter motor solenoid.
In the photo above, the arrow with the "+" symbol indicates the BAT connection of the solenoid.
A common problem is the battery cable's terminals corroding on one or both ends, causing a false-contact connection problem.
Corrosion developing on either terminal end will prevent the starter motor from receiving all of the battery's current and won't crank the engine.
So, in this test section, you'll perform a simple multimeter voltage drop test to check the condition of the cable. The result of your voltage drop test will show if the starter is getting the battery's full power.
Place your multimeter in Volts DC mode.
Attach the red multimeter test lead to the positive (+) battery post. The positive (+) battery post must be clean and corrosion-free.
You may need two helpers for this test step, since someone will have to hold the red multimeter test lead onto the battery positive (+) terminal bolt and someone else inside the vehicle (to crank it when everything is set up).
Place the black multimeter test lead on the starter motor solenoid stud that connects to the battery positive (+) cable (see illustration above).
The orange arrow with the plus (+) sign, in the illustration above, points to this stud.
Maintain the black multimeter test lead in this position throughout the next step.
When everything is ready, have your helper turn the key to crank the engine.
Although the starter motor won't crank the engine, your helper has to turn the ignition switch to start the engine for the voltage drop test to work.
The multimeter should register 0.5 Volts or less (0.5 V = 0 Volts).
If there's a problem in the wire, your multimeter will register some voltage, usually 5 Volts or more.
Let's take a look at what your results mean:
CASE 1: Your multimeter indicated NO voltage drop (which is 0.5 Volts or less). This is the correct test result and it confirms the starter motor is receiving full battery power to crank the engine.
You can conclude that the starter motor is bad and needs replacement if you have:
- Confirmed that the starter motor does not crank the engine (TEST 1).
- Confirmed that the starter motor is receiving an activation signal (TEST 2). If you haven't done this test yet, please do so now.
- Confirmed, in this test section, that the battery positive (+) cable does not have a voltage drop issue.
Now, before you remove the starter motor, do one more important thing:
- Turn the engine manually (using a 1/2 ratchet and the appropriate socket on the crankshaft pulley bolt). This will check to see if the engine is mechanically locked up (or not).
If you'd like to bench test the starter motor (after removing it). You can find the step-by-step instructions here:
CASE 2: Your multimeter registered 5 Volts or more. This result confirms that the starter's battery wire has corrosion or a false-contact issue (and that's not a good thing).
The issue causing the voltage drop in the wire will prevent the battery's total amperage output from reaching the starter motor.
You should thoroughly clean both ends of the battery positive (+) cable to solve this problem.
I recommend using sandpaper to clean the cable's terminals. Once both ends of the battery positive cable are clean, reconnect everything and try cranking the engine.
If cleaning the cable ends solves the voltage drop issue, the starter motor will now crank the engine.
More 3.1L Chevrolet And Pontiac Diagnostic Tutorials
You can find a complete list of 3.1L Chevrolet Cavalier and Pontiac Sunbird tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The Fuel Pump (1990-1994 3.1L V6 Chevrolet And Pontiac Vehicles).
- How To Test The TPS (1990-1994 3.1L V6 Chevrolet And Pontiac Vehicles).
- How To Test The Alternator (1990-1994 3.1L V6 Chevrolet And Pontiac Vehicles).
- How To Test The Engine Compression (3.1L V6 Chevrolet And Pontiac Vehicles).
If this info really saved the day, buy me a beer!