|06-25-2008, 09:59 PM||#1 (permalink)|
So many times, I see people have starting problems with their car, and they are quick to blame the battery or the starter. Other times, I see people say, "no, it can't be the starter, it's gotta be the solenoid."
Here is some testing you can do with a Digital Multimeter ( ) or Digital Volts/Ohms Meter (DVOM). This article is about testing on a Vulcan Taurus but most starting systems are very similar and these basic tests can usually be performed the same way. Remember to have the red lead of your meter in the volts port and the black lead in the common port. Also, be sure to set the meter to volts.
It is easier to get at the starter from underneath, so you can jack the car up if you want, but it doesn't need to be jacked up.
First, look at your symptom.
Is it a slow crank or a no crank? If it is a slow crank, you know that the solenoid is working properly. You can eliminate the possibility of the start circuit from the ignition switch being bad. If there is a no crank, listen for a loud "click." This click is from the solenoid. If you can hear that click, you can eliminate the start circuit. If the solenoid does not click, first test the battery voltage and make sure it's fully charged. Hold the red meter lead to the positive terminal and black lead to the negative terminal.
If the battery has less than 12.4 volts, it will need to be charged before these tests can be performed. If it has 12.4 volts or more, you may proceed. One more thing to remember is, if you are testing a slow crank, disable the fuel by pulling out the fuel pump relay or disconnecting the inertia switch. Your best bet is to disconnect the inertia switch with a Ford because some Ford's power the through the fuel pump relay and the is needed to allow the car to crank on most newer models.
To do an available voltage test on the start circuit, place the negative lead on the negative battery terminal and the positive lead on the start terminal on the solenoid. On many cars, the start terminal is the smaller of the three and can have a meter lead with a gator clip easily attach to it. However, on the Taurus (not sure about all model years, but the third gens have this), there is a plastic connector in place of a normal terminal. This will need to be backprobed with a pin (do not backprobe the connector with a large pin, it needs to be skinny or you will damage the connector). While watching your meter, have a buddy try cranking the motor, you should read somewhere close to battery voltage (a volt or two less is normal as there is usually a massive draw on the battery when starting). If you see less than that, there is excessive resistance in the start circuit and it must be located and repaired. The start circuit varies from car to car and further diagnosis will require some more electrical skill and a wiring diagram.
If the start circuit is ok, and you can hear the solenoid click on, then you may proceed to the rest of these steps. Please remember to make sure that the battery has more than 12.4v before each individual test is performed. If the solenoid does not click on, the solenoid may be bad or it may not be getting a good ground. Refer to the ground side checks later in this article.
Here is a look at the terminals on the starter solenoid:
The 2 big terminals may be underneath a plastic cover like this:
Be sure to check the battery posts and all those terminals for dirt and corrosion and clean dirt and corrosion out of the terminals before moving on. A simple bad connection could have been causing your issue the entire time. Don't forget to make sure that the little strap that goes from the starter terminal to the starter isn't damaged or broken.
Once that is out of the way, start by checking battery voltage again, except this time, have a buddy try to crank the motor. If the voltage drops below 9.6v, it is very possible that your battery is bad. Bring it to Autozone, Advance Auto Parts, or another auto parts store that does free battery testing. A battery load test will tell you for sure if the battery is truly bad.
If the first test passes, it's time to do a voltage drop test between the actual battery post and the terminal on the battery cables. Place the red lead on the positive post and the black lead on the positive cable terminal and have a buddy try to crank.
Then, repeat the test on the negative terminal. This time, putting the black lead on the negative post and the red lead on the cable terminal. On both these tests, almost no voltage should be dropped. Any more than .2v is excessive and even that is pushing it. If excessive voltage is dropped, clean any dirt and corrosion from the battery posts and terminals and retest.
Once that test is passed, it's time to do a voltage drop test of the positive cable. Do this by placing the red meter lead on the positive battery terminal:
Then, clip the negative lead to the B+ (Battery Positive) terminal on the solenoid:
Once both leads are connected, have your buddy try to crank the motor. If you read a voltage drop of .5v or more, then there is excessive resistance in the cable and it needs to be replaced. Before you replace the cable though, double check the B+ terminal on the solenoid to make sure it isn't full of dirt and corrosion. If it is, clean it out, reconnect it, and retest to make sure that it really was the cable that was dropping the voltage.
If that test passes, you will do a voltage drop between the B+ terminal and the Starter terminal on the solenoid (the 2 big terminals). Place the red lead on the B+ terminal and the black lead on the starter terminal and have a buddy try to crank the motor:
You should see no more than .2v dropped. If you do, clean the terminals of any dirt and corrosion and retest. If you still have an excessive voltage drop, then the contacts are worn out in the solenoid and the solenoid must be replaced.
If that test passes, you can move on to a voltage drop test of the ground side. If you were skipping ahead because the solenoid would not click, but the start circuit was good, this is where you want to start testing the ground side. This test is very simple to peform. Place the black lead on the negative battery terminal:
and then touch the red lead up against the starter case and have a buddy try to crank. You need a clean surface with no paint on the starter. If the starter is painted, you'll have to scratch a small spot off to touch bare metal. My starter has some of the paint conveniently chipped off of it:
You should see no more than a .2v drop. If that is the case, check all your grounds (including the starter bolts) and make sure they are all clean and tight. Clean any dirt and corrosion out of your ground connections and retest. If you skipped to the ground side test because the solenoid wouldn't click and it still will not click, the solenoid is bad and needs to be replaced.
If the solenoid does click, and all other tests pass, then the starter is bad and needs to be replaced. Double check yourself and have it tested at an auto parts store before buying a new one. You wouldn't want to buy a starter only to find that you made a mistake when doing the starter voltage drop tests.
Also, remember, if the solenoid clicks rapidly. It usually means that there is a bad connection at the battery terminals, the battery has a low charge, or the battery is bad. Check the battery terminals and have it charged and load tested at your local auto parts store.
I figured this would be good for the "Solutions to common problems and How To" forum, if there are any major errors that I overlooked, please point them out. I'm pretty tired right now and could easily have overlooked a mistake.
Currently driving a 2009 Focus SE Sedan w/5-Speed!
1997 Geo Prizm
1996 Ford Taurus G
Formerly "Mr. X"
|06-26-2008, 01:27 AM||#2 (permalink)|
Crazy Devoted Member
Here are some printable PDFs I got off AutoZone's webiste on starter testing. Pretty much the same steps.