The hydrogen gas has nothing to do with anything electrical. It could be the reason the battery exploded. You have to understand an exploding battery is extremely rare because we warn about safe handling practices all the time. Any conscientious mechanic is going to want to know why that happened before he worries about anything else. Batteries don't explode for no reason. Next, when you have corrosion on the cables, the battery is on its way out and is about to fail. The coatings you spray on don't stop the corrosion, they just neutralize it. As the lead flakes off the plates, which happens in all batteries, there is less plate material left to absorb the current coming in so they get warmer and make the acid bubble. The bubbles reach the top of the battery case and forces acid out next to the posts. It builds up there forming the corrosion you see. That's why it only happens to older batteries that are about to fail within the next six months or so.
As for your park / neutral switch, there are two possibilities. Most commonly there are multiple parts to the switch. One part allows the starter to crank the engine in "park" or "neutral". A different part may tell the engine or transmission computer which gear is selected. A second potential problem could be that one time you didn't have it solidly in park when you tried to start the engine. Simply moving the shift lever a little would solve that seemingly insignificant problem but that would be enough to be detected and set a fault code. If that is the case, you should be able to erase the code and it won't come back. If the code does come back for that switch, it is likely not related to the starter circuit part of it. The Check Engine light is supposed to turn on when any stored code is related to a problem that could have an adverse effect on tail pipe emissions. The Engine Computer may be changing ignition timing or fuel metering in park to give a smoother idle, for example. If the computer doesn't know when it's in gear it might continue to supply too much fuel while you're driving. That would increase emissions. The point is, it might be detecting a problem that is not related to the starter circuit.
As for the alarm, start by checking the fuses and electrical connectors near the battery. If acid sprayed on them there is no way to know what damage was caused. Diagnosis of that might have to be done by the dealer. Also, sometimes fuses blow just from installing a new battery. The current surges from the computers' memory circuits charging up can cause blown fuses. That's actually pretty common. Once replaced, those circuits work fine.
Wednesday, March 9th, 2011 AT 5:32 PM