TEST 3: Bypassing The Radiator Fan Switch

How To Test Radiator Fan Motor Relay (Honda 2.2L, 2.3L)

In this test step... we're gonna' test all of the circuits of the fan relay by bypassing the radiator fan switch with a jumper wire.

This is a very simple test but you do need to take one very important precaution and it's to use a small diameter jumper wire (gauge-wise).

This is to prevent the jumper wire from damaging the radiator fan switch's pigtail connector's female terminals.

NOTE: On 1998-2001 Honda Accords, the radiator fan switch is located on the thermostat housing.

OK, this is what you need to do:

  1. 1

    Disconnect the radiator fan motor from its pigtail connector.

    NOTE: The radiator fan relay must be in its place on the under-hood fuse box for this test to work. Also, your Honda's engine should be cold to avoid burns.

  2. 2

    Jumper the pigtail connector's 2 terminals.

    IMPORTANT: Use the smallest diameter wire to jumper these two circuits. If you use anything thicker (gauge-wise) you could permanently damage the female metal terminals.

  3. 3

    Turn the ignition switch to the On position, but don't start the engine (this test is done with the Key On Engine Off -KOEO).

  4. 4

    The radiator fan motor should activate, as soon as you turn the key to the On position (KOEO).

Let's examine your test result:


CASE 1: The radiator fan motor came on. This is the normal and expected test result.

This test result tells you several important things:

  1. The radiator fan motor relay is good (otherwise the fan would not have come on).
  2. The radiator fan motor and fan motor relay fuses are NOT blown (otherwise the fan would not have come on).
  3. The wires between the fan switch and radiator fan motor relay are not shorted (otherwise the fan would not have come on).
  4. The wires between the radiator fan motor and radiator fan motor relay are not shorted (otherwise the fan would not have come on).

Therefore, if your Honda Accord is overheating (and the radiator fan motor is not coming on), you can correctly deduce that the fan motor switch is bad and needs to be replaced.

CASE 2: The radiator fan motor DID NOT come on. Recheck your jumper wire connections and retest.

If the fan motor does not come on, then you have eliminated two important components as bad:

  1. The radiator fan motor.
  2. The radiator fan motor switch.

You can deduce that the radiator fan relay is bad since you have:

  1. Done TEST 1 and you have power in the relay socket terminals #1 and #3.
  2. Done Test 2 and the fan came on when you jumpered the relay socket terminals #1 and #2.

Suggestion: If I where in your shoes, I would now swap this relay with another on the fuse box and repeat this same test. If the fan motor now comes on, I now know that the radiator fan relay is truly fried.

TEST 4: Bench Testing The Radiator Fan Relay

How To Test Radiator Fan Motor Relay (Honda 2.2L, 2.3L) How To Test Radiator Fan Motor Relay (Honda 2.2L, 2.3L) How To Test Radiator Fan Motor Relay (Honda 2.2L, 2.3L)

If you still have doubts that the radiator fan relay is good, you can bench-test it by manually applying power and ground to it and seeing if circuit #1 and #2 show continuity (as tested with a multimeter).


Image 1 of 3 and image 2 of 3, in the image viewer, are an actual example of how your jumper wire and multimeter test lead connections should look like.

NOTE: The power and ground source that you'll be using is your Honda's car battery.

These are the test steps:

  1. 1

    Connect male spade terminal #4 to ground, using one of your jumper wires.

  2. 2

    Connect male spade terminal #3 to the battery's positive (+) terminal. This will energize and activate the relay. This can be confirmed by the audible click the radiator fan relay will make.

  3. 3

    Measure the resistance across the relay's terminals #1 and #2 with your multimeter in Ohms mode (as seen in the photo).

  4. 4

    Your multimeter should show continuity. If it doesn't show continuity, recheck all your connections and retest.

  5. 5

    Remove and reconnect the jumper wire to terminal #3 several times, as you eye-ball the multimeter.

    When the jumper wire IS NOT connected to power, the multimeter should show NO CONTINUITY.

    When the jumper wire is connected to power, the multimeter should show continuity.

Let's examine your test results:


CASE 1: Your multimeter showed continuity. This test result tells you that the radiator fan relay is good.

CASE 2: Your multimeter DID NOT show continuity. Recheck all of your test connections and retest. If your multimeter still doesn't show continuity... then the radiator fan relay is fried and needs to be replaced.

More Honda Accord Tutorials

You can find a pretty big list of Honda Accord tutorials in this index: Honda 2.2L, 2.3L Index of Articles.

Here's a small sample of the tutorials you'll find in the index:

  1. How To Test The Radiator Fan Motor (Honda 2.2L, 2.3L).
  2. How To Avoid A Blown Head Gasket (Honda 2.2L, 2.3L).
  3. How To Test For A Blown Head Gasket (Honda 2.2L, 2.3L).
  4. How To Test For A Broken Timing Belt (Honda 2.2L, 2.3L).
  5. How To Test The Igniter, Ignition Coil Accord, Civic, CRV, and Odyssey (at: easyautodiagnostics.com).