Help! I'm not a mechanic

[chrisrad]

Yesterday, I did the most intelligent thing. I disconnected the battery cable while my toyota was running to test the alternator (a common practice when I was younger and taking car advice from friends and my dad). This morning I read that I could destroy my computer, stereo, alternator, etc by doing that. How would I tell if I have messed up something. I have not had to work on a car since my 1984 trans am and things have apparently changed drastically since then.

Your thoughts would be greatly appreciated!

Chris

[V-8Fan]

Well, try out all the stuff you mentioned, and if it all still works, and you don't have a check engine light, you probably hurt nothing.

I would like someone to explain to me how doing what you did could damage anything though, because I can't imagine how it would.

[Polygon]

Everything being computer controlled, cutting the energy suddenly could be damaging. Though not likely it is a possibility. They are just covering their butts.

[V-8Fan]

Yes, I agree. Computers need to be turned on and off via a switch to prevent surges and transients from damaging them. But if you remove the battery leads, as chrisrad described with the engine running, then the alternator is providing power for the computer the very instant the battery is disconnected. I do not see how the computer would ever know at all that the battery had been taken out of the circuit.

[Moppie]

Its possible to creat a surge in the system when you remove or reconnect the battery leads, its the same with jump starting a car with any kind of computer controlled engine mangment system.

And it dosnt take much to destroy or badly damage an engines ECU, and they are not cheap to replace.


When jump starting any ECU equiped car you should always use leads with a surge protector fitted, or isolate the batter on the donnor vechile be removing its earth lead.
And once the car has been started, let it idle for a few minutes to even out any current flucuations between the two batteries, before disconecting them, starting always with an Earth lead.