by Keith Hamburger

Created on: April 23, 2008

If you are having trouble starting your Honda the first step to take is diagnostic and, possibly, replacement of the main relay. Design improvements after around 1995 has made this relay more reliable and, after around 2005, the main relay was divided into two parts. However, if your Honda is much older than about ten years, this is a common problem area.

The main relay in Honda automobiles is essential to your car's operation. Actually two relays in one, the main relay controls power to the car's computer and to the electric fuel pump. Diagnostics and replacement of the relay is quite simple, especially if you have a little bit of experience with electrical troubleshooting. The only tools that should be necessary for this would be an electrical meter capable of measuring voltage and resistance and a pair of jumper wires, preferably with alligator clips on the end.

In addition, since the specific terminals vary for different years and makes you should have a shop manual with a wiring diagram for the car. It might be possible to search the Internet for the specifics on your vehicle but that's not guaranteed. You could skip the resistance troubleshooting portion of this diagnostic but if you do you might end up spending between $50 and $100 replacing a part that wasn't the problem.

When you turn the ignition key to on, but before you try starting your car, you should hear two solid clicks from the relay. One is turning on the ECU and the second powers the fuel pump. Before you turn the key to start you might hear a softer click after two seconds. This is the fuel pump turning back off after it pressurizes the system. When you turn the key to start and crank the engine you should hear a third click. Since the starter will be cranking at this point you may actually need to put your hand on the relay and feel this one.

If any of these actions are missing there is a good chance that the relay has failed. If all are missing you may wish to check for a failed fuse.

The better test for the function of the relay is to provide power to the proper terminals to activate each portion of the relay and check for a closed circuit. This diagnostic isn't particularly difficult but if you don't have the diagrams to tell what terminals are the correct ones, or if you've never done this type of testing, you can likely skip this test. If the relays are working properly in this case you will need to check elsewhere to diagnose your problems.

Removal of the relay is quite simple. It is

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