What causes relays to buzz? [Archive] - DSM Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum: DSMtalk.com

: What causes relays to buzz?

07-21-2003, 04:35 PM
I thought I would try a more general approach to my relay question since I'm not getting any responses in the detailed approach.

So what would cause a relay to buzz?



ATF 2GTalon
07-22-2003, 01:54 PM
That's like asking why power lines hum. They hum because of the frequency of the electrons moving thru the wire. And also the fact that electric currents create electromagnetic fields around the wire causing anything magnetic (ie polarized air) to line up and move in a certain direction which causes furthur disturbance in the air thus creating a hum. I tried to simplify as much as I could.

07-22-2003, 03:30 PM
The buzzing is quite loud... like a door buzzer. It also prevents me from starting my car.

It is the ASD/MFI relay. I know a situation can occur when a certain amount of current flows, the electromechanical armature on a normally closed relay will open, breaking the circuit and the armature closes again. Then the cycle repeats causing the buzzing sound.

What I don't know is:

Is it because the ECU is seeing a problem with the crank or cam sensors and is trying to open the circuit (which would cause the car not to start) or if this a voltage probem I.E. too much voltage or not enough.

Appreciate the input

07-26-2003, 07:16 PM
If your relay itself is humming very loud it is obviously bad(hence the car not starting), i have had a few different relays do that to me on different things, it could be mosture it could have recieved a short, or it could just be bad,, i had one do that to me and if you taped it on something it would work.. until next time..

Have you tried replacing it. (i know that sounds like a dumb question but that will ussually work,)

07-26-2003, 08:01 PM
if this a voltage probem I.E. too much voltage or not enough.

Since I do this everyday at work, I can tell you they will hum(buzz) at undervoltage and lock it tighter at higher voltages til the coils open and die.

I don't know what relay you are talking about so I can't help you more.

07-27-2003, 03:39 AM
It is the ASD/MFI relay

08-03-2003, 08:21 AM
a DC relay will hum due to the undervlotage that 95tsiawdgst talked about... this could be caused by a short circut on the load side of the realy, the short pulls the voltage down enough to let the contacts open, which birngs the voltage back up and the whole cycle keeps repeating.

or it could be a bad connection in the wire going to the coil, the coil could cause the bad connection to heat up, the resistance goes up with heat, and the voltage goes down

08-06-2003, 06:46 AM
also as a side note, it could be the coil "aging" since it does heat up and causes the varnish to wear thru allowing certian parts of the coil to short, thus decreasing the number of turns and length of the conductor, depending on how sever it is it could drop voltage below the minimum allowed in design, or just low enough that the coil can not produce a high enough of a magnetic field to pull and hold the contact in place, hense the chatter. Best thing to do.

Ensure via a DMM you have correct operating voltage going to the spade style contact. (where it plugs in). then find a local DSMer buddy who will let you borrow his. If his makes it go away, try cleaning your contacts first with alcohol or a pencil eraser. If its still there, then replace.

My evap solienoid does it, as well as the more annoying power antenna, so I am stuck listening to CDs all the time. but that gives me the chance to convert from power to solid non adjusted mast style antenna and save a little weight.

Let us know how things go.

08-06-2003, 07:47 PM
Thanks for posting guys. I've replaced the relay with a brand new one (I also tried a used one but since it was used I couldn't trust the results) and the relay still chatters. Not really sure what else to do. I've checked as many connectors and wires as I could find but found nothing. I did the fuel pump rewire, I didn't really expect this to fix the probelm. Any other ideas?

Thanks again

08-08-2003, 08:58 PM
Hrmm... all I know to do would be trace the wireing back (the electrical diagram in the service manual would be helpful) to any switch, connection ect. and see if anything is loose, or in any way a bad connection.