Readers react to issues from disconnected battery

An ounce of prevention is worth a pound of cure. This old adage aptly sums up a sensible approach to disconnecting batteries from unfamiliar vehicles.

My columns in recent issues of Tire Business (March 4, March 18) describe the potential perils of disconnecting a battery from a vehicle without providing auxiliary power to it beforehand.

A battery disconnect may erase some of the memory inside on-board computers temporarily, causing strange symptoms after a technician reconnects the battery to the vehicle.

In my March 18 column, I described a technique for providing auxiliary power to a vehicle prior to disconnecting its battery for any reason.

Some readers have responded to these topics with interesting questions.

First, a fellow asked about the consequences of disconnecting the battery on a 1993 Cadillac that he stored for the winter. An educated guess on my part — a hunch — is that disconnecting the battery on a relatively simple 1993 vehicle shouldn't cause much trouble.

Of course, he would have to reset the car's digital clock. Thereafter, this car probably would perform fine after he drove it for a short time.

However, I'm reluctant to make hard, fast judgments — especially on unfamiliar vehicles. Battery disconnect has fooled me.

For example, I'm doing homework on a car at a service shop or tire dealership. A task requires disconnecting the battery; I gamble that a simplistic-looking vehicle won't suffer if I disconnect its battery without attaching auxiliary power to it first.

But after I reconnect the car's battery, the automatic transmission shifts late and harshly.

Then it takes 30 minutes of road testing to normalize the transmission again. This extended road testing enables the car's transmission computer to "re-learn" its normal values for shift timing and shift quality.

Recently, I saw a flummoxed customer return to a shop with a 2017 Subaru WRX.

Ordinarily, briefly touching the power window button in the up direction made the window rise completely. Momentarily touching the button in the down direction lowered the window completely.

But following the repairs the shop performed, this automatic up / down feature didn't work. Instead, the owner had to hold the button in the up or down direction to raise or lower the window completely.

Fortunately, a Subaru specialist buddy of mine clued us to a simple reset procedure for the windows' automatic function following a battery disconnect.

But mind you, this is just one example on one modern vehicle. What other surprises are out there?

Another reader inquired about connecting auxiliary power directly to a battery's terminals instead of the diagnostic connector under the dashboard.

You see, since 1996, a typical vehicle has an industry-standard diagnostic access connector somewhere under the left side of the dashboard.

The connector's terminal 4 is chassis ground; terminal 16 is battery power. Adapter cables are available that neatly and quickly link your auxiliary power source to these terminals inside the diagnostic connector — and therefore, to the car's electrical system. Sliding the appropriate adapter onto the underdash connector is a snap.

This fellow wanted to connect auxiliary power directly to the battery's terminals with jumper wires and alligator clamps.

Although this approach is technically correct, it may be awkward and counterproductive. You see, a battery's location and terminal type (top or side terminal) may make it difficult to keep alligator clips securely connected during the battery disconnect / reconnect procedures.

I've watched techs accidentally dislodge the alligator clips from the battery terminals during these maneuvers.

In my experience, linking auxiliary power to the underdash diagnostic connector with the appropriate slide-on adapter cable is the easiest, most-secure method.