My 2005 Max has a buzzing relay every time I start the car in the morning when the engine is cold. The buzz disappears after the engine is running. The relay, blue and white in color is located on the passenger side under the glove compartment near the door side. When the relay makes noise, the starter does not want to work as if there is not enough juice even though I have a new Optima battery installed a few months ago. I tried to identify the source of the problem but so far cannot determine why it makes a buzzing sound except that when I pull out the fuse from the fuse box under the hood on the passenger side that says "AT CONT," that relay stops making noise. Another thing I notice is that when this relay is buzzing, all controls relating to air/heat and fan are not functioning. Does anyone experience similar problem? Do you know what this relay is for and the meaning of the label AT CONT? This problem just happened about a week ago and cannot be duplicated when the engine is warm.

 

Guessing: Automatic Temperature Control? There is a door that controls the amount of fresh air coming in.

On the passenger side is the ECU and the tramsmission control module. No other relays are listed on the diagrams.

If you have the patience you can search through the service manuals.
Download from http://www.vq35de.com/ESM/Nissan/

 

Thanks for the info re AT CONT. That gives me a good start to troubleshoot the problem. The relay is buzzing like crazy before the engine starts. Once I was able to start the engine, the relay stopped, and the buttons controlling vent, aircond, fan, heater etc can be operated upon. Maybe something is stuck. I'll find out. Thanks again.

 

The problem continue to happen and today the care does not start. I pull the fuse labeled as AT CONT and try 7 times before the engine is alive again. The problem cannot be duplicated until the next morning so dealer would not be able to identify the problem. I could not find out the name of that relay in the manual. Does anyone who is an electric guru could identify what this is all about. I hope the problem to be a malfunction relay but have no way of testing it. Any help would be greatly appreciated.

 

Finally I put my old OEM battery back and the buzzing problem is gone. I measured the voltage of the red top optima and it was 12.1 volts. Purchased less than 8 months ago at Costco this 720 cca is defective! I went to Costco today and exchanged for the new one, no problem. Installed to the Max and it is running fine. I'll wait for a few days to make sure the problem is truely gone. By the way, I weighted both batteries. The OEM is 40 lbs, and the Optima is 34 lbs.

 

A lot of folks here praise OPTIMA, but IMO, no matter what the brand is, some car batteries will be defective. Just shows OPTIMA is not perfect either. Glad it solved your problem.

 

I have a 2004 maxima and after driving for a while when i come to a stop i hear a buzzing sound which seems to be coming from under the hood. But when i turn my car off and then start it again the noise is gone. Has anyone had this happen, and if so can you tell me what it may be?