Electrical noise when car is off.

[josiahrock]

when my car is off there is a electrical noise that sounds like a motor thats coming from below the engine by the radiator. my radiator fans turn on and off when i turn the ac on and off, so i dont think its coming from the radiator. I used a microphone to locate where the noise is coming from and its loudest by the circular wheel with rubber sides located in the middle right of the attached pic. what is that called? i also see wires going into it or underneath it. any ideas of what it might be would be awesome. thanks
heres a link to the pic http://www.flickr.com/photos/josiah-pat ... 006111281/

[tigersharkdude]

I think what you are showing by "circular" is your motor mount. Its probably your fans mang. Seriously, your fan can stay on for like 10 minutes after you turn off

[loystock]

If you have electronic engine mount, then it's showing symptoms (whirring/buzzing sound) that it is on the way out. The bad part is that when it eventually shorted out, it can fry the ECU (expensive to replace). You have to disconnect the electrical connector for that particular engine mount. You can leave the other engine mounts as is.

[parksmopar]

What are the purpose of the electronic engine mounts?

[tigersharkdude]

I want to know too. Never heard of one

[the converted]

Softens up when your cruising on the highway and stiffens up when you get on it. It was a way for Nissan to try and make the ride nicer. I'm not sure if they continued onto the 6+ gens, but they started in the 5th's and only on auto cars.

[loystock]

AFAIK, the electronic engine mounts are designed to reduce vibration at idle, especially on a cold engine. The ECM commands the mount to soften at idle and stiffen beyond 1500 RPM. The FET power transistor (by NEC) is inside the ECU. Unfortunately, when the electronic engine mount is short circuited, aside from blowing the NEC power transistor in the ECU, it may also cause the other FETs in proximity (like the FET for Idle Control) to fail. You may end up with a troublesome P0505 trouble code. And dealer will usually recommend replacing the ECU, IACV and motor mounts... OUCH!

A short circuit in the IACV stepper motor or Electronic Motor Mount may 'kill' the ECU. If you are good with soldering, you can probably replace the 'fried' component(s) yourself. But too much heat may impair the transistor while a 'cold solder' may render it erratic.

Disconnecting the electronic engine mount connector will revert it like a regular mount. No trouble code will be generated as it is an open loop (command sent by the ECU to the mount is not monitored). You may not even know the difference, especially if your engine is in good condition.

[parksmopar]

Thanks man.. I was wondering about that.

[BLAXIMA_78]

AFAIK, the electronic engine mounts are designed to reduce vibration at idle, especially on a cold engine. The ECM commands the mount to soften at idle and stiffen beyond 1500 RPM. The FET power transistor (by NEC) is inside the ECU. Unfortunately, when the electronic engine mount is short circuited, aside from blowing the NEC power transistor in the ECU, it may also cause the other FETs in proximity (like the FET for Idle Control) to fail. You may end up with a troublesome P0505 trouble code. And dealer will usually recommend replacing the ECU, IACV and motor mounts... OUCH!

A short circuit in the IACV stepper motor or Electronic Motor Mount may 'kill' the ECU. If you are good with soldering, you can probably replace the 'fried' component(s) yourself. But too much heat may impair the transistor while a 'cold solder' may render it erratic.

Disconnecting the electronic engine mount connector will revert it like a regular mount. No trouble code will be generated as it is an open loop (command sent by the ECU to the mount is not monitored). You may not even know the difference, especially if your engine is in good condition.

I had the same issue with my 1992 GXE. it would buzz after i turned the key off and it would drain my battery. when i put a stethacope up to the car, it sounded like it was coming from inside my transmission bell housing. my car also stays in third gear and doesnt shift...any clues?

[BLAXIMA_78]

i had an electrical short to power near the front relay box. installed a 50AMP fuse and now the transmission shifts near perfect. next is the slow transmission flush, pulling the injectors for a rebuild, a new exhaust flex pipe and the alignment. yay me. i love people who sell cars without EVER doing any maintenence...sheer bliss.