How to Test Your Honda Main Relay

DIY Honda Car Maintenance

Main relay diagram for testing reference.
Refer to this chart detailing the terminals of a Honda main relay. about.com library

From time to time, vehicles can have a wide range of electrical issues -- even those that are reliable like Hondas. One of those problems can involve the relay. You may not have to rush off to a mechanic to test to Honda main relay. Instead, just use this simple test.

What's an Auto Relay?

Just about every vehicle on the road today includes automotive relays. Basically, these components allow one circuit to switch another on or off.

 For example, if you plugged in your headlights into a headlight switch, you may surpass the amperage rating and cause an electrical blunder. The relay works as a conductor in between a low amperage circuit, allowing it to turn a higher amperage circuit on or off. These parts are vital to ensure proper electrical function -- not to mention safety -- in a vehicle.

Relays can also switch power at the same time using a single output, such as if you activate your radio and the antenna goes up at the same time. 

The main relay in a vehicle controls the fuel pump and supplies power to the injectors. Knowing how to test a Honda main relay can help you better pinpoint electrical issues in a vehicle.

How to Test the Main Relay in a Honda

There's a pretty simple way to tell if your main relay is affected. Simply turn on the vehicle and see if it continues to run. If so, the main relay is okay. Should it shut off, the main relay in your Honda could be impacted.

 

If you suspect you have a bad main relay in your Honda, you should perform this test to be sure. It can save you time, money and aggravation as most parts suppliers don't take returns on electrical components. This is why it's important to avoid buying a part you don't need.

If your Honda is suffering from hot start problems that affect cranking, this diagnostic test might be helpful, too.

These steps make references to the illustration below, so consider printing it out to help while you're working. Here's the test:

  1. Remove the main relay.
  2. Attach the battery positive terminal to the No. 4 terminal and the battery negative terminal to the No. 8 terminal of the main relay. Then check for continuity between the No. 5 terminal and No. 7 terminal of the main relay. If there is continuity, go on to Step 3. If there is no continuity, replace the relay and retest.
  3. Attach the battery positive terminal to the No. 5 terminal and the battery negative terminal to the No. 2 terminal of the main relay. Then check that there is continuity between the No. 1 terminal and No. 3 terminal of the main relay. If there is continuity, go on to Step 4. If there is no continuity, replace the relay and retest.
  4. Attach the battery positive terminal to the No. 3 terminal and battery negative terminal to the No. 8 terminal of the main relay. Then check that there is continuity between the No. 5 terminal and No. 7 terminal of the main relay. If there is continuity, the relay is just fine. If the fuel pump still does not work, keep testing down the wiring harness toward the fuel pump. If there is no continuity, replace the relay and retest.