Magazine for the auto service professional
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22 | ASP June 2016 Technical interior lights and their control unit were still drawing current. Battery test Once the current drain is found and fxed, you need to determine if the battery can still be trusted. But before you test it, there are a few other things to consider. If properly cared for, a battery can live twice as long as its warranty rating. Te useful life of a battery is afected by heat, vibration and depth of discharge. Consider the vehicle and how it's typically used, and consider the age of the battery and what kind of abuse it may have sufered. Does this vehicle live in a hot climate? Is it used of-road? Is it a kid hauler used mostly for short trips by a busy parent who can't always make sure all the lights are switched of? Sometimes you can make the decision without testing the battery. Two diferent tools can be used to test a battery; a load tester and an electronic conductance tester. Te load tester directly measures the battery's ability to deliver current, while the conductance tester measures the ability of each plate to conduct electricity. Either tool can tell you if the battery is OK or if it should be replaced, but only when it's used according to the tool maker's instructions. If you don't have those instructions, go to the company's website and get them. Using these tools incorrectly will produce inaccurate test results and you'll either condemn a good battery or, even worse, send a customer away with a bad battery. Te most common reason for inaccurate battery test results is incorrect identifca- tion of the battery. Te tester compares the battery's measured performance with its expected performance, which is expressed as cold cranking amps (CCA), reserve capacity (RC) or amp hour (Ah) rating. Te tester may also consider the battery's group size, the physical dimensions of the battery, which has an infuence on the battery's performance over time. If you can't accurately provide the information the battery tester needs, you won't get an accurate test. Battery replacement Once you've decided to replace the battery, be aware that you may need to use a scan tool for a charging-system-relearn procedure. Also, it's absolutely critical to install the correct battery for that vehicle, especially if the vehicle has a stop/start system. Te PCM controls the charging system, and it's programmed for specifc features like battery technology (fooded or absorbed glass mat), group size and sometimes even the electrical equipment spe- cifc to that VIN. Installing the wrong battery may prevent the charging system from working correctly and/or generate charging system fault codes. Driveability issues or problems with the gauges on the instrument panel are other signs of a mismatch between the battery and the charging system. Battery technology is advancing rapidly, but the diagnostic techniques described here will always be useful for testing a battery that powers the starter. Since it only takes two minutes, practice the DVOM min/max test on every car that comes through your bay so you can learn what known-good looks like. One of most useful tools you have is your own experience. ■ With the circuit operating a standard 1156 light bulb, we measured a voltage drop across this fuse of 10 millivolts probing these two points. The chart indicates a current fow just shy of 3 amps. Jacques Gordon has worked in the automotive industry for 40 years as a service technician, lab techni- cian, trainer and technical writer. He began his writing career writing service manuals at Chilton Book Co. He currently holds ASE Master Technician and L1 certifcations and has partici- pated in ASE test writing workshops.