Auto Service Professional

JUN 2016

Magazine for the auto service professional

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14 | ASP June 2016 Technical Battery testing 2.0 Tat clicking sound doesn't always mean a bad battery By Jacques Gordon S ometimes diagnosing a no-crank/ no-start problem can be more difcult than diagnosing a driveability problem. Te average passenger car or light truck has at least two dozen electronic control units on-board, and luxury vehicles can have three times that many. Some of those tiny electronic brains can make a decision that will drain the battery almost overnight. For driveability diagnostics, we at least have the advantage of OBD II trouble codes that are the same on every vehicle. Electrical systems and electronic equipment can be diferent from one vehicle to the next, even on the same model in the same model year. Tis makes it harder to answer the two questions you face with every no-start: Why is this battery dead, and should it be replaced? One of the most common tools in your shop can help you fnd the answers to battery questions: a digital volt-ohm meter (DVOM). You'll need more than this to test the battery itself, but you can test everything that draws current from the battery with a DVOM, and that can tell you if the battery's demise was natural or premature. Opening shot Usually the frst sign of battery trouble is slow cranking speed during starting. Tat Let's face reality. Most drivers don't know their car bat- tery is going bad until their car doesn't start. That's when being a professional can separate you from the DIYer who simply replaces the battery without any diagnostic test- ing. Remember to ask the driver of the vehicle probing questions to see if the problem is really just a worn-out battery, or if something else is happening. At this point, it's time to do your diagnostic check, and also explain why this is important to prevent a comeback. Make sure the customer knows you provided a service, and didn't just replace the battery. Take your readings directly from the battery posts, not the clamps. This ensures a more accurate reading.

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