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How To Test Your Main Relay

Testing the Main Relay in Honda Cars

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Main relay diagram for testing reference.

Refer to this chart detailing the terminals of a Honda main relay.

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NOTE: If the car starts and continues to run, the main relay is okay.

Before you start replacing this or that, if you suspect you have a bad main relay in your Honda, you should perform this test to be sure. Most parts suppliers don't take returns on electrical components, so buying a part you don't need will really hit you in wallet with this one. If your Honda is suffering from hot start problems, this diagnostic test might be helpful, too. The steps below make references to the illustration below, so you might even want to print it out for 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 OK; 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.
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