Keyless Entry Module blew up, Need INFO

[shoon]

Driving along yesterday and my radio and clock crap out... so I replace fuse #8, and it blows 5 seconds later. Hmm.. thats weird.

So, I pop the trunk to check the trunk light wiring hoping maybe a wire got pinched and that's it... until I see a cloud of smoke coming out of my keyless entry module!

I opened up the module and found there is a black capacitor "MOV1" that exploded. Can anyone give me the writing off the front of it so I can try replacing it? And if that doesn't work, and I were to replace the module does that mean my keyless code will have changed?

So WTF?

Oh, just prior to the second fuse blowing I also noticed that when I hit the unlock button, my headlights turn on, but the lock button still works. So is it likely a short in the module or the wiring? Right now the module is unplugged so I can at least have a radio... no interior lights, or power locks, or trunk light

Anyone had this happen to them?

 

[Pro*banshee]

No but can you get a picture of the offending area? Looking at the circuit I'll be able to tell you if you need a specific value capacitor, or if it's just a power-filtering cap that can be substituted with anything

 

[hawkeye18]

"MOV1" is not a capacitor. It's a Metal Oxide Varistor. MOVs are used as last-ditch fuses for when current is shorted to ground. When they blow, something is seriously wrong.

They also have a lifespan, and will blow just because they are getting old. One would need to figure out the value of the MOV in order to replace it, otherwise you won't get the protection that it's meant to provide.

 

[shoon]

Getting a GOOD picture might be a bit tough with my cellphone, I traced back the one leg of the capacitor, and it connects to the + side of 3 diodes paralelled together (I think its positive, its the side of the diode opposite the silver line).

so, I'm thinking its just a filter capacitor. Any idea what would cause one to blow? cracked ceramic / voltage spike?

EDIT:

Hawkeye, is it possible to substitute the MOV for a glass fuse of some sort? And is it more probable something is shorted, or more likely just blew because of age?

 

[shoon]

Doing some more research, pins 4 and 5 are keypad ground / signal ground and pin 1 is Battery +.

Right now the MOV is shorted 0.1 ohms.. meaning this mov is shorted straight to ground.

Now im wondering, did the MOV fail because of age, and by hitting the unlock button and having the headlights come on, was that a result of the spike from the shorted MOV or is it likely something else?

I removed the MOV, and pins 1 - 4,5 are no longer shorted together. I'm skeptical about plugging this back in, any ideas?

OH, found this on MOV's http://www.americanelectriclighting.com/Products/DTLtechdocuments/photocontrolsurgeprotect.asp

They are supposed to be high resistance.


EDIT:

Well, went out and plugged it in after chopping off the MOV and everything works perfectly!

 

[hawkeye18]

Your RKEM is now unprotected against circuit spikes. You'd better hope the MOV failed due to high age.

 

[shoon]

Yea, I originally thought the module was a goner; obviously the MOV was installed for a reason, so I'll leave the module unplugged for now.

Come to think of it, it wasnt until I was pulling out of a drive thru that I noticed the radio was dead, the surge from rolling my window down might have done it.

If anyone has a spare Keyless entry module they can crack open, can they please let me know what the MOV is rated for so I can replace it?

TIA,

Shaun

 

[Storm-Chaser]

I agree with Jason (hawkeye) that you're taking a big risk here.

I too would simply replace the module. You may end-up spending as much on replacing the MOV, as you will buying a used Keyless Entry Module. The 5-digit code will be prominently displayed on the module itself, and it's very easy to reprogram it to your key fob.

Since you mention two of the keypad circuits appear shorted-to-ground, I would pull the door panel and disconnect the keypad as part of trouble shooting the problem. If it is shorting-to-ground, you'll likely blow either the replacement MOV or module, whichever you end-up replacing.