280 Warning Horn Keeps Coming On

[wagoetzmann]

I have a 2005 Mercury 280 OS. The warning horn has started coming on once I run the engine up past 5K-6K rpm. When the rpm's are decreased the horn goes off. The water pressure is 15 psi and water is coming out of the tale tell hose. The head temperature reads 135 F. The engine starts and runs fine. Sometimes I can shut the engine off and when I restart it the problem goes away. Yesterday this did not work however. It seem when the horn comes on power is reduced automatically by the computer? What could the problem be?

(This is the same post as in the General Discussion section.)

[Chummy]

Hook it up to a CDS and see what it says....if the horn went off it logged a fault.

[wagoetzmann]

Where can I buy a CDS?

[Chummy]

You can't you have to take it to a Mercury Servicer... most of them will usually scan it and just let you know what fault it was for little or no charge.

[chad202]

Sounds like it could be just a faulty sensor.

[hydrostream1]

You can use the DDT scanner as well,providing the scanner has the smartcraft cartridge in it.There`s a code in it,could be oil sensor related,water in the fuel filter on the engine it has a sensor in the bottom.

[flabum1017]

There are several thing it CAN be. I had an Optimax that had similar symptoms and it turned out to be a bad teriminal connection it the oil pump sensor plug. If you're not real familiar with these, your best bet is to let a pro check it for you.