Battery, Starter and Charging system testing

Diagnosing a bad battery or starter can be relatively simple in most cases. A common sense approach and some simple tests can save you some money instead of needlessly "throwing parts" at a problem and aggravating yourself.

First make sure the terminals are clean and tight. Simply try to twist them and see if they will move. If so they are too loose and need to be tightened. Look for signs of corrosion which can cause a bad contact between the battery and the terminals. If so clean them. A mixture of about one table spoon of baking soda and about 6oz of hot water will neutralize and eat away most of the corrosion, but you still need to use a good Battery terminal cleaner to get a solid contact.

Turning on the headlights to see how bright they are can sometimes be a good indicator of the available voltage in the battery. Bright headlights indicate a decent charge and dim lights will mean you are probably going to need to charge the battery. I dont recommend jump starting anymore because todays vehicles with computers are just too sensitive to voltage spikes. I have seen many cars towed in to the shop with several hundred dollars worth of electrical damage because somebody hooked the jumper cables up backwards and the sad thing is it is usually the vehicle that was trying to help that gets the short end of the stick. So if you have to jump start make sure its hooked up right or there are jump boxes available now which are handy when you need one especially if there is not another car around.

A good multimeter is hard to beat for testing electrical systems. They vary in price and as always you get what you pay for, but it is usually more money, gets you more features. Make sure to read the directions and get familiar with your multimeter before you start using it. Like anything else electronic, they can be damaged easily and render them useless.

  The battery should read between 11.8 - 12.5 volts with the car not running. If your battery registers somewhere around there and it still will not try to start, then maybe it is time to take a look at the starter. If you are not satisfied at this point that the battery is not the culprit, you may want to take it and have it load tested at any local auto parts store. A load test will show the available amperage of the battery. This means they will put a load on the battery to see how much "power" it has to crank the engine, and they usually do this for free.

    Now that you are positive you have a good battery and connections, with the headlights on, have a friend try to start the engine. If it cranks over slowly or if the headlights still try to go dim then the starter may be too worn out to start the engine efficiently and may need to be replaced.With a multimeter the voltage should read about 12.5 and then drop sharply to around 10 volts when you try to start it. If it seems to have no effect on the battery, it could be the starter solenoid has an "open circuit" meaning it has disconnected itself somewhere on the inside.

  The next step would be to check the connections on the starter. Make sure they are also clean and tight. With a multimeter or a test light  check for voltage at the starter. Most starters have two wires one big one and one liitle one. The big one almost always will have voltage all the time whether the key is on or off. It is the main power cable for the starter. The little one is the control wire for the starter. Have a friend try to start the vehicle while connected to this wire. It should light up when they try to start it. If so then it is a good bet the starter has seen better days. If it does not light up or if you have no voltage while trying to start it then you need to start looking elsewhere, checking fuses would be a good start. Beyond that the starting circuits get pretty in depth and may be better left to a qualified technician.

    The alternator control circuit varies so widely on different vehicles i cannot give you the information you need to diagnose an alternator correctly. Some vehicles have an external voltage regulator. Some have an internal regulator, and then others are computer controlled and can get quite complicated diagnosing those types of charging systems. What all of this means is that if the alternator is not charging the vehicle it does not necessarily mean the alternator is bad. If the control device, like the regulator or the computer is not telling the alternator to charge, then it just simply will not charge.

   What you can do yourself is find out if the alternator is charging or not. It is fairly straight forward, with a multimeter hooked to the battery it should read 13.5 -14 Volts if it is your in good shape. If not, i highly recommend having a qualified technician diagnose the problem.

    Car batteries can be extremely dangerous. They can explode with little provocation. Hooking the jumper cables up backwards, dropping a wrench on the terminals when cleaning them and overcharging them are all ways to ruin your day. People are chemically burned by battery acid all the time, so take care not to let it get on you or your clothes (It will not wash out of your clothes, if it does you can try adding a little baking soda to the wash water to neutralize the acid.) Immediately wash it off your skin. If you get it in your eyes keep flushing them with water and call 911 immediately.