Testing a 'does not crank' problem can sometimes be a challenge since so many things can can cause it.
With this case study, I'll explain some of the basic testing/troubleshooting steps that are usually done to test for a DOES-NOT-CRANK condition (this is a condition in which the engine does not turn over). You should be able to see that:
- These tests do not require expensive tools or testing equipment.
- That they are very easy to perform.
- These testing guidelines apply to any vehicle you may be driving or repairing.
- The different causes of a DOES NOT CRANK Condition.
- How to test a BAD STARTER MOTOR and by extension how to eliminate a BAD BATTERY as the cause of the problem.
Although the test steps in this case study were done on a 3.8L GM vehicle, the basic troubleshooting applies to any type of vehicle.
Contents of this tutorial:
You can find this tutorial in Spanish here: Pruebas Cuando No Arranca -Estudio De Caso (GM 3.8L) (at: autotecnico-online.com).
Alright, let's get started. Here's how it all happened:
Is It The Battery Or The Starter Motor?
It's bad enough you're having to run around all day long doing errands (on a cold day to top it off) and in the middle of it all; the car dies on you as you're driving down the road, yeah, the icing on the cake! Lucky you, you were able to coast into a parking lot where you try to get the car to start but it won't cooperate.
If this were to really happen to you, I'd say, the first thing to go thru' your mind would be that the starter went bad. Well, I take that back, maybe that wouldn't be the first thing, 'cause I'm sure (if I were in your situation) there would be some other very choice thoughts/words come in and out first.
Well, getting over the initial 'Why me?' frustration, you ask yourself- Is it the starter or is it the battery.
Not knowing what's going on, you finally decide it has to be the battery. After asking a thousand people to help you to jump-start the car you finally find a good Samaritan to help you. After thirty minutes of trying to jump-start the car, it still won't start. The engine will not turn over. Why can't this stuff happen on a beautiful and very sunny 70 degree (°F) day?
Out comes the cellphone and after what seems like an eternity, finally the tow truck arrives (kinda' like our friendly boys in blue, never around when you really need them but always there to man a speed trap).
This is exactly what happened to a customer, of the auto repair shop where I work, involving his 1998 Oldsmobile Intrigue. This case study has a twist to it, since the problem was neither the battery nor the starter motor.
There are many things that can cause a 'no-crank no-start' condition. In this article, I'll tell you what I did to narrow down the search for the 'truth' and arrive at the correct conclusion. The test method I'll be describing is simple and can be applied to the majority (if not all) of cars on the road today. So read on my friend.
A NO CRANK-NO START CONDITION is usually one of the easiest problems to test and solve and with this case study, I'll show just why this is. Not to mention that having the right info (no baloney) makes a difference in testing the starter motor. Lets read how it all happened.
But before I go on, let me just say that the biggest reason (that these are the easiest problems to solve) is that there's a specific flow of: step 1 test this, step 2 test that, and so on and so forth that are performed to arrive at the correct conclusion. So, keep reading and I'll show you how it works:
In The Bay, Troubleshooting Starts
The customer's 1998 Olds Intrigue rolled off the tow truck and into my bay. I thought to myself that this was gonna' be the easiest job of the day. A case of a bad battery or a bad starter, the diagnosis and repair would be like taking candy from a baby (boy was I wrong). The owner had already provided us with the story of how it happened and when it happened. Now it was up to me to find out the 'what happened' part of it.
The very first thing I needed to know was the state of charge of the battery. I whipped out my trusty multimeter and tested the voltage of the battery. And the voltage was at 12.7 Volts and not only that, the battery was brand new. Now knowing the battery was fully charged, I got into the vehicle and tried to start the engine.
I heard the starter solenoid activating but not much of anything else. The engine was not turning over. Battery or starter? Now the fun was gonna' start 'cause the reason the car is in front of me is to make sure I replace the correct part and the customer spends the money on a solution and not a guess.
Whether it's the owner or a service writer selling the job, the last thing he or she wants to know is that after replacing the part or parts I recommended, the vehicle still has the exact same problem. Oh the pressure of it all!
Voltage Drop Test
OK then, I called out to one of the guys to come over and help me out by turning the ignition switch to the START position while I did a voltage drop test on the starter's voltage input wire. This is the heavy gauge wire that comes directly from the battery.
I placed my multimeter in Volts mode. I attached an alligator clip adapter to one of the multimeter's leads (it doesn't matter which because the polarity of the leads does not matter) and connected this to the battery positive (+) terminal bolt (this is a GM vehicle with a side terminal type battery). With the other multimeter's probe I touched the center of the big stud coming out of the starter solenoid (this is where the battery positive cable is fastened to). I then had my buddy CRANK the engine and again, just the loud click from the starter but the multimeter showed no voltage drop.
This test told me that full battery voltage and thus current were reaching the starter motor. I didn't have to worry about oxidation in this circuit diminishing the current to the starter.
Just to tie up any loose ends and since I was already testing one starter motor circuit, I tested (with my Power Probe) the starter signal coming from the ignition switch. This circuit too, was getting it's full complement of voltage. On the next test.
I then did the voltage drop test on the Ground circuit of the starter motor by placing one end of the multimeter's lead on the battery negative (-) terminal bolt (using the alligator clip adapter) and the other on the starter motor body (the starter is Grounded thru' its case). And once again, had my buddy turn the ignition switch to the START position. Remember, a voltage drop test has to be done with the component in action! The test showed that the Ground was good.
So far nothing, yet any automotive diagnosis is simply a process of elimination. With the above tests I had just eliminated quite a few components/circuits. The specific components/circuits I had just eliminated above where: the battery, the power and Ground circuits of the starter, and the circuit between the ignition switch and the starter.
Knowing that the battery was good. The next test was to bench-test the starter.
