TEST 2: Making Sure The Starter Is Getting An Activation Signal
As I mentioned in TEST 1, when you turn the key to start the vehicle, it's the 12 Volts start signal that causes the starter to crank the engine.
This start signal can easily be checked with a multimeter or a 12 Volts automotive test light. We'll do that in this test section.
NOTE: You can use a multimeter or a 12 Volt automotive test light (although the following test steps assume you're using a multimeter).
OK, here's what you'll need to do:
Lift the vehicle and place it on jack stands (if it isn't already up in the air).
Connect the red multimeter test lead to the S terminal wire of the starter motor.
You can either test for this signal with the S terminal wire connected to the starter motor or not, your choice.
Connect the black multimeter test lead to the battery negative (-) post.
Now, have your helper crank the engine.
The engine won't turn over, but the idea is to verify that the starter motor solenoid is getting the 12 Volt start signal from the ignition switch.
Your multimeter will register one of two results:
1.) A voltage between 10 to 12 Volts DC.
2.) No voltage at all.
OK, let's make sense of the readings that your multimeter recorded in the test:
CASE 1: Your multimeter registered a voltage between 10 to 12 Volts. This test result lets you know the starter solenoid is receiving the start signal (crank signal).
This means we can forget that the safety-neutral switch and ignition switch are faulty. OK now the next test is a very simple and easy voltage drop test. Go to: TEST 3.
CASE 2: If your multimeter DID NOT register 10 to 12 Volts. This result exonerates the starter motor. Your starter motor is not bad.
Here's why: Without that 10 to 12 Volts start signal, the starter will not crank the engine. While it's beyond the scope of this article to test the neutral-safety switch or the ignition switch, you've eliminated the starter motor and that means saving money by not buying a part your vehicle doesn't need.
TEST 3: Voltage Drop Testing The Battery (+) Cable
One of the things I've seen quite a bit in my long years in the trenches as an automotive technician is corrosion on the battery terminals, causing a voltage drop that leads to an engine no-crank problem.
Now in case you're wondering what the heck a voltage drop is in the case of the starter motor (and any other electrical circuit), it's anything that causes some or all of the voltage and current flowing into the circuit NOT to reach its final destination.
I'm sure you've probably already cleaned the battery cable terminals and battery posts, but there's still a good chance that hidden corrosion (on the positive battery cable) is preventing full battery power from reaching the starter motor.
The absolute best way to rule out this possibility is to do a simple multimeter voltage drop test of the positive battery cable (which attaches to the large stud on the starter solenoid).
OK, to get started, this is what you need to do:
Place your multimeter in Volts DC mode.
Attach the red multimeter test lead to the center of the positive (+) battery terminal.
If the positive battery post isn't clean, then clean a spot right on the top of it. It's important that the multimeter test lead make contact right in the center of the positive battery post.
NOTE: 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 and someone else will need to crank the vehicle while you perform the next step.
With the black multimeter test lead, touch the center of the starter solenoid stud to which the big battery cable attaches to.
NOTE: You'll maintain the black multimeter test lead in this position throughout the next step.
Now, have a helper turn the key to crank the engine from inside the vehicle.
This is important, since a voltage drop test has to be done while the component in question is working (or trying to work).
Your multimeter should register 0 Volts (0.5 Volts is still 0 Volts).
If there's a voltage drop, your multimeter will register voltage (usually above 7 Volts DC.)
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: Your multimeter registered 0 Volts (no voltage drop). This result indicates that the starter motor is receiving all of the battery voltage and amperage it needs to crank the vehicle.
This also means that the starter motor is bad, and here's why:
- In TEST 1, you confirmed that the starter motor does not activate when you apply power to the starter motor solenoid S-terminal wire.
- In TEST 2 you have confirmed that the starter motor receives a crank signal.
- In this test step you have confirmed that no voltage drop exists on the battery positive (+) cable.
These 3 test results taken together indicate that the starter motor is defective. Replacing the starter motor should resolve your engine's no-crank problem.
I'll give you two more recommendations.
- Before removing the starter motor, manually rotate the engine using a 1/2 ratchet wrench and appropriate socket on the crankshaft pulley. This is just to make sure the engine or A/C compressor is not locked-up and causing the no-crank problem.
- Bench-test the starter motor after removal. This is a super easy test and you can find the tutorial here: How To Bench Test A Starter Motor (Step By Step) (at: easyautodiagnostics.com).
CASE 2: Your multimeter registered 5 Volts or more. This result tells you that a voltage drop does exist and this is not a good result.
The good news is that this is easily corrected as a voltage drop is always caused by some sort of corrosion problem on the positive (+) cable or the battery positive (+) post.
The solution is to thoroughly clean the battery positive (+) post and the battery positive (+) terminal (both the end that connects to the battery and the end that connects to the starter solenoid).
After cleaning, try cranking the engine. If it cranks and starts, no further testing is required.
More 1.8L Nissan Sentra Tutorials
You'll find a complete list of 1.8L Nissan Sentra tutorials in the following index:
Here's a small sample of the articles/tutorials you'll find in the index:
- How To Test Engine Compression (2000-2006 1.8L Sentra).
- How To Test For A Blown Head Gasket (2000-2006 1.8L Sentra).
- Mass Air Flow (MAF) Sensor Test Nissan Sentra 1.6L (1995-1999) (at: easyautodiagnostics.com).
- How To Test The 2000-2002 Nissan Sentra 1.8L MAF Sensor (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!