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Charging system issues and fixes

Monday, April 2, 2018 - 06:00
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To prevent problems and save time, it’s wise to look up the specifications in service information and verify voltage at the control module with a scan tool, not just by placing a multimeter across the battery terminals before and after the vehicle starts and check that the voltage is 12.0 and goes up to 14.0 when it’s running. It’s important to verify that the control module sees correct battery voltage and isn’t commanding loads be shed or reduced.  

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It’s also still important to check voltage drop across the heavy cables and also pin grip at the smaller terminals in the system when diagnosing charging system faults – female connectors can lose grip after being disconnected and reconnected as few as three times. In other words, it doesn’t take much to cause a problem and paying careful attention to details is the best way to quickly and accurately find the cause. It’s that attention to detail that makes the difference now. 

Also be sure to check fuses and fusible links for problems if something seems strange – all of them. We had a Honda Civic towed to the shop completely unresponsive, and it wouldn’t be boosted or power up. Turns out the main fusible link was blown. The customer tried to boost the vehicle themselves – backwards, which they didn’t mention – and the vehicle needed not only a battery but the fusible link replaced as well (the fusible link did its job and did indeed protect the rest of the system from damage). Sadly, customer behavior just doesn’t seem to change even though their vehicles sure do. 


Despite what’s currently posted online, the days of removing the negative battery cable while the vehicle is running to diagnose a faulty alternator have been over for a very long while (and let’s be honest, that was never a good test or a good idea to start with) and the days of accepting 12 volts across the battery terminals before cranking and 14 volts at the battery with the vehicle is running (measured with a voltmeter) as proof that the charging system was problem-free are gone as well. Diagnosing charging system problems on newer vehicles requires service information and the proper diagnostic tools – and a bit of experience knowing what to look for and where. But if you’re ready for it, diagnosing and repairing charging systems can help those diagnostic tools pay for themselves quickly. 

It’s definitely worth learning about what’s new with charging systems over the past few years to prevent headaches and reduce diagnostic time – and maybe even prevent some embarrassing situations from ever occurring. Charging systems are more critical than ever, and there’s certainly money to be made repairing them – which is still important, indeed.

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