Maintaining vehicle power during routine automotive repairs is essential to preventing needless comebacks on sophisticated modern vehicles. Fortunately, performing this task is very simple on the majority of vehicles tire dealers service. In my last column, I explained that disconnecting the battery in a modern vehicle is similar to losing power to your personal computer (PC). If a passing storm knocks out the power to your building and you haven't saved the latest data you entered into your PC, that data is lost.
Likewise, some of the memory inside automotive computers (ECM's, TCM's or PCM's) is lost when the vehicle's battery goes dead or is disconnected for any reason. Losing this memory (commonly called ``learned'' or ``adaptive memory'') can cause various performance problems.
Suppose the customer brings a vehicle in for a new battery or other repairs seemingly unrelated to the electrical system. What he or she didn't know is that many repairs require disconnecting the battery cables for safety or serviceability reasons.
For instance, good technicians disconnect a battery cable to prevent accidental arcing and sparking during routine repairs. Or a tech may have to disconnect a negative battery cable because it's either attached to or literally obstructing access to the component he's replacing.
All the customer knows is that his car acts strangely after he leaves your tire dealership. When he returns screaming that his car didn't act like that until your techs touched it, he's not lying!
Many service personnel have learned the hard way that talking your way out of this situation is difficult, if not impossible.
To make matters worse, the consequences of a disconnected battery vary a great deal from vehicle to vehicle. Many techs will contend that the only consequences of disconnecting a battery are resetting the car's clock and radio station selections—until he or she encounters the ``disconnect from hell!''
I think the following suggestions are practical ways to address the battery disconnect issue. First, consider making it shop policy to safely connect back-up power to a vehicle before disconnecting its battery for any reason. When in doubt, always follow the vehicle manufacturer's recommendations.
However, the general trend in providing back-up power has been to connect a fully charged automotive battery to the vehicle's cigarette light socket or auxiliary power port. In case you haven't noticed, many vehicles have a cigarette lighter-shaped socket somewhere on the dashboard or console that provides 12-volt power for accessories such as cellular telephones, radar detectors, etc.
On most vehicles, the lighter or auxiliary power sockets are ``live'' all the time, so it's a simple matter of connecting a spare battery to the socket with a safe, convenient adapter sold by any of the mobile tool dealers that call on your dealership.
Many service shops keep relatively compact, lightweight and rechargeable ``power packs'' handy for jump-starting batteries of stranded customers. These power pack devices are ideal back-up power sources.
In the unusual case where the lighter socket isn't constantly live, the tech must locate an alternative hook-up point that is.
Years ago, some techs used an adapter to connect a 9-volt battery to the lighter socket. Although a 9-volt battery will maintain the presets on an electronically tuned radio, it doesn't have enough energy to provide the back-up power needed for today's vehicles. Reportedly, using a 9-volt battery for back up can cause accidental air bag deployment!
If you don't connect back-up power beforehand, at least write down the radio station selections so you can reset them afterward. Furthermore, allow time for adequate road testing after the battery is reconnected. The only way to restore learned or adaptive memory after the battery goes dead or is disconnected is to drive the vehicle.
Experience shows that ECM's, TCM's and PCM's can re-learn adaptive values within 20-30 miles of driving.
If a tech, service writer or helper restores the radio station presets and road tests the vehicle, everything should appear normal when the customer drives off. Just remember: They don't like unpleasant surprises after the repair.