Electrical - Battery Replacement Precautions

Replacing a Battery? Don't Disconnect the Cables

With the

Engine Running

When replacing a battery, many service techs disconnect the battery cables with the engine running to keep the data alive in volatile memory. This practice worked fine back in the day when vehicles were pretty much a box on wheels, but with so many of today's vehicles sporting a impressive array of cool, high tech hardware, it's not recommended. Here's why:

^ The battery works as a capacitor to prevent sudden swings in voltage. With the battery cables disconnected, the alternator voltage regulator tries to stabilize the system voltage, but it can only do so by turning the alternator on and off.

^ When solenoids or relays are turned on and of{ they produce a very high voltage spike that travels through the 12-volt system. This voltage spike can fry sensitive solid state components or corrupt the data that's stored in volatile memory for such components as the gauge control module, the radio, and the various control units.

The best way to keep data alive in volatile memory when replacing a battery is to hook up a Honda Computer Memory Saver to the 16P data link connector (DLC). This portable tool works as a secondary 12-volt source. It saves you the hassle of writing down your customer's audio presets, resetting the clock, or even doing the idle learn procedure.





The Honda Computer Memory Saver is indeed a real time saver, but here's a word of caution: Don't let the positive battery cable touch any body ground. It will cause a short that will either blow the fuse in the tool or cause a drop in system voltage resulting in the loss of any data that 5 in volatile memory.

The Honda Computer Memory Saver is available through the Honda Tool and Equipment Program. To order one, just call and ask for FZRMS4000H.