Unpleasant consequences of disconnected battery

Date: Mar 6, 2019

Disconnecting a vehicle’s battery may create costly, unpleasant surprises for tire dealers and service shop operators.

In this column and my next one, I’ll discuss the potential pitfalls of battery disconnect and recommend sensible precautions.

Blithely detaching a battery cable or cables may erase memory — commonly called learned values — which on-board computers have accrued during normal driving.

When these values are erased, a vehicle may run poorly after a technician reconnects the battery cable(s). Worse yet, a technician and/or shop foreman may not realize why the car runs worse than it did when it arrived.

Remember that re-establishing these learned values could require considerable road testing.

Usually it’s difficult to charge for this additional time on any given repair job. Plus, demanding the additional time may look suspicious to the car owner.

However, the costliest aspect of this procedure may be the fact that it upsets your service department’s already-tight appointment schedule.

For openers, proper procedure for certain repairs dictates disconnecting the vehicle’s battery first. Naturally, disconnecting one or both battery cables shuts down the entire electrical system — including all the vehicle’s on-board computers.

Years ago, there were only two adverse effects of disconnecting a battery. First, a technician had to reset the clock on the dashboard.

Second, he had to reset the station selections on a customer’s electronically tuned radio. But electrical systems aren’t quite that simple today.

For example, the more-common vehicles that your techs service these days may have a multitude of on-board computers.

The greater the number of computers, the greater the potential risk of losing learned values after a battery’s disconnected.

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