While it sounds obvious, the battery is often overlooked when dealing with an electrical problem. Actually, the battery should be more of a maintenance item than a repair issue. I have to think by now all successful import specialist shops are relying on maintenance work to keep their bays profitable. Checking and servicing the battery should be part of that maintenance program. Things like dirty battery cables and a low fluid level should never be a problem on a car that is serviced regularly. Of course, we do see cars that have these problems. When you do, don’t hesitate to use it as an opportunity to point out the value of a good maintenance program. It’s important to remember that a good battery and charging system is critically important to the operation of the electrical system.
Like everything else in this business, we’re seeing some computer-based battery/charging testers that will perform many tests with the push of a button. I’m sure these machines work as advertised and, if you have one, by all means use it. But we know they’re not absolutely necessary to perform an accurate diagnosis of the systems we’re examining. Follow along as we diagnose the charging and starting system on a Mazda using a DVOM and a two-wire test light.
STARTING SYSTEM DIAGNOSTICS
The first step is to confirm the battery condition. Start by checking the battery with a hydrometer. If the hydrometer test shows a good state of charge, disable the ignition system and crank the starter for about 30 seconds, noting the voltage. It shouldn’t drop below 8 volts and return to the 12.5 you should have started with. Reconnect the ignition and start the engine. You’re looking for the alternator to increase the voltage by 1.5 to 2 volts; no increase means that system is not charging. If it is, the next step is to put the system under load by turning on electrical accessories like the heater fan, rear defrost and high-beam headlights. At 2,000 rpm, the alternator shouldn’t allow voltage to drop below the 12.5 volts you had with the KOEO.
This is also a good time to check for proper operation of not only the charging system warning lamp but also all of lamps. Be sure the battery lamp lights in the KOEO position and goes out when the engine is started. While it’s no guarantee the system is charging, it can make the diagnostic process easier if it’s not. It also lets you know that the customer would have no warning if it were an intermittent problem. The importance of the other warning lights operating properly is obvious.
For this example, we’ll use a 1997 626, but before you do any testing, be sure to refer to your service information. While the strategy of all the systems is similar, execution will differ by model. For example, the Prot