Why you should remove the negative battery terminal before doing ANYTHING!!!!

I personally have seen a bunch of blown ECU's caused by wiring shorts, mostly fuel pumps, but other things too.

Sure the ECU is 'protected' by a diode, but no one sells the damn diode to replace the blown one nor do many 'authorized' places exist to fix them. Half are sunk in a block of plastic also.

I have repaired a few by using a cheap diode with a +/- 10 to 15% tolerance so they fell close to the original specs. Close enough to work.

If the dome light is on a timer, it is connected to some kind of computer....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > I was lokking thorugh the Subaru manual to find out where the thermostat

First you said that the bulb was in pieces, not that the glass was broken. Was it really broken? I have seen several times that the glass part of a bulb can separate from its socket but still hanging by the leads it may still work. And I have also seen that the ends of a broken lamp filament can dangle together and get get kind of welded together, so it works again, but usually not for long. What may kill an ECU is the very very short transients in voltage when a cirquit somewhere in the system is abruptly opened or closed, especially when it is high current (a short) and/or repeated many times. If he made a momentarily short cirquit while changing the bulb that MAY be enough. That is why with modern cars we are advised not to use jumper cables without transient suppressors.

Asbjørn

Hello:

This might seem odd to you but, newer cars use bulbs that are a specific impedance. A 2157 is the same candle power as an 1157, but the impedance is higher. That's why if you use a 2157 in place of a 3057 for argument's sake.

You'll get a check eng>

excellent. and it's /well/ below any level that could /possibly/ impact the ecu!

indeed.

You seem to forget that the dome light is 'live' all the time using a ground as a switch.

They can have the glass fall out of the base and the loose internal connecting wire(s) can and will cause a short circuit. This happens all the time with bulbs such as the 1157 in taillights.

Short circuits can do nasty things to computers like blow the input diode 'before' the fuse has a chance to blow.

It's not like the designers of modern vehicles are just BSing when they say to unhook the negative before working on them.....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08

Hachiroku ???? wrote: \

I don't buy it. ECUs are actually *very* well protected against intermittent faults, voltage spikes, etc. (Zener diodes are a wonderful thing). 99.9% of the "failed" ECUs people pull out of cars are actually fine and the problem lies elsewhere. There's no WAY you can hurt one just changing a light bulb.

That much is not true in all cases. Any care that has "theater fade" interior lights, for example, has them powered from a computer module (not necessarily the engine controller, but a "body controller" or some other computer module.)

And on all of THAT, I agree completely!

Think "fuse" in this case.... unless it was one of those Chinese-made fuses from Harbor Freight... ;-)