2007 Ford Mustang electronics

It will not damage anything, but there are some things to be aware of. On a lot of newer cars like yours, the engineers cleverly designed in a lot of tricks to force you to go back to the dealership. VW in particular has multiple computers that lock up simply from disconnecting the battery to replace it. The transmission won't come out of "park", and if the engine starts, it won't rise above idle speed. You have to drag them off the hoist and onto a flatbed truck for a trip to the dealership to have the computers unlocked. To add to the misery, for liability reasons, almost every repair procedure you can think of starts with, "disconnect the battery".

GM used to be famous for this too with their radios locking up. Now that is also common on almost all import vehicles. There are a number of cars that we have been warned about where this is NOT a problem, but it is something you want to consider.

Also be aware that a battery that is allowed to remain discharged will start to sulfate. Hard lead sulfate will build up on the plates. That will prevent the flow of current through those plates, and you may never be able to bring the battery back to where it can reliably crank the engine. A better alternative is to connect a small float charger or a small solar panel battery maintainer. If you don't want to do that, disconnect the battery's negative cable to prevent the many computer memory circuits from discharging the battery. The industry standard, unless specified otherwise, is those computers can be allowed to draw a maximum of 35 milliamps, (.035 amps). At that rate, a good battery will be able to crank the engine fast enough to start after sitting for three weeks.

I have to correct a couple things here. I work at a shop that specializes in Euro cars and there is nothing intentionally built into these vehicles that will "lock out" computers. It is possible that having an extended period with no battery power cold cause isolated modules to lose their programming but that rarely prevents the car from starting or operating. The car will lose memory for personalized options like driver preferences and auto windows may have to be initialized again but that can be done without any equipment. Honda radios will go into security lock but the owner only has to enter their unlock code.

GM radios are programmed with the VIN# of the vehicle they belong to so they cannot be installed into a different vehicle but they can be removed and replaced within the same vehicle with no problem. That also applies to dead batteries in that vehicle.

I admit that disconnecting batteries, especially for extended periods can SOMETIMES cause havoc with programmed electronic modules but nothing is intentional and many Independent repair shops are capable of resolving these issues.

Hi Wrenchtech. You're the second person to put my mind at ease.

The story I got was from six years ago from a Carquest instructor who owns a shop in Jolliet, IL that specializes in the one out of a hundred cars all the other shops have given up on. Their main customers are other shops. They network with manufacturer-based instructors all over the country as well as other people who put on these high-level classes. When they gather enough information about a model or system, they develop a class for the mechanics from independent shops who don't have the chance to get factory training. Those classes used to cost $1200.00 for 12 two-night classes. Much of what he covered was over my head, and I had a hard time remembering all the details, but one of the things that stood out was a Volkswagen they got in his shop. After disconnecting the battery and reconnecting it, it wouldn't come off idle, (throttle-by-wire system), it wouldn't come out of park, and it had to dragged off the hoist and skidded onto a flatbed truck for a trip to the dealer to have the computers unlocked. That instructor is much smarter than I can ever hope to be, so I'm sure he had already checked fuses and things like that. The point is he spent a lot of time describing how the systems worked, and he stressed the importance of using a memory saver.

I haven't run into a module losing its customer settings yet, although I'm sure it's possible. Exovcds is another VW expert here. He was the first person to say I was wrong about the dirty tricks some manufacturers dream up, but he also admitted in one of his conversations that a locked transmission was possible. I forgot what the fix was, but it did result after the battery was disconnected and some other work was done. Thanks, Wrenchtech, straightening me out.

We all know crazy thing can result from disconnecting power from electronic systems but it's not intentional.