Electrical Problems on a Mazda

Well, I took my car (2009 Mazda 3 GT, Auto) to a highly reviewed shop nearby to have some routine maintenance done. They replaced the brakes (new rotors) in front, did a transmission flush, new air filters and an oil change. When I picked up the car, I noticed the car door ajar light was on even after I repeatedly assured myself that every door was latched tight. Also, the auto headlights no longer worked and the power lock on the doors did not work. I told the technician right away, and he said that they are probably just frozen (note: this visit to my local mechanic coincided with a fierce arctic blast and the temperatures have barely climbed above zero in the last 4 days). If things didn’t change the next day, I should contact them. Well the next day I needed a jump from my neighbor. I thought perhaps the door ajar light was a slow drain on the battery, but then I couldn’t start the car just three hours later. So, I went ahead and got a new battery, as mine was four years old and a gas station nearby had Interstate Batteries on sale for $69. I had hoped that connecting a new battery would reset the electrical system and fix the other problems, but no.

Any thoughts on what could be causing this? Should I never trust this mechanic again?

With the heavily computerized cars we have today, a problem like this may require a visit to the dealer. I am just assuming, but it sounds like you have a failure in the convenience module, although each car maker tends to call it by a different name, and it may require specialized equipment to determine that. This equipment I know the dealer should have, but most independent shops may not. These modules are supposed to control the auto-headlight system, courtesy lights and door sensors, and other functions. A bad module can drain a battery. A simple mistake, like a voltage spike during a jumpstart, can damage these modules.

Thanks for the help. For the time being, it seems to have resolved itself.