How to Test Radiator Fan Motor Relay (2001-2005 1.7L Honda Civic)

This tutorial will walk you through the process of bypassing your 1.7L Honda Civic's radiator fan relay and bench testing it (by applying battery power and ground to its internal coil).

These two are pretty easy and simple tests and I've included all of the illustrations you need to get the job done without complications.

Since in this tutorial we're only troubleshooting the radiator fan motor relay and its circuits... you'll find the radiator fan motor test here: How to Test the Radiator Fan Motor (2001-2005 1.7L Honda Civic).

Here are the contents of this tutorial at a glance:

  1. Symptoms of a Bad Radiator Fan Relay.
  2. The Basics of the Radiator Fan Relay.
  3. START HERE: The Radiator Fan Motor Relay Tests.
  4. TEST 1: Checking the Radiator Fan Relay Power Circuits.
  5. TEST 2: Bypassing the Radiator Fan Relay.
  6. TEST 3: Bypassing the Radiator Fan Switch.
  7. TEST 4: Bench Testing the Radiator Fan Relay.
  8. Where to Buy the Radiator Fan Relay and Save.
  9. More Honda Civic Test Tutorials.

En Español You can find this tutorial in Spanish here: Relé Del Ventilador Del Radiador (1.7L Honda Civic) (at: autotecnico-online.com).

Symptoms of a Bad Radiator Fan Relay

Since the radiator fan motor relay is one of the main components that gets your Honda Civic's radiator fan motor to run.. when it fails the most obvious symptoms that your Honda Civic will experience is overheating.

You'll also see one (or more) of the following symptoms:

  1. Your temperature gauge will max out (as you're driving around).
  2. Your Honda Civic will not re-start (once it has overheated).
  3. Coolant (or water) boiling in the radiator's overflow tank as the engine runs or when you turn off the engine.
  4. Coolant boiling in the radiator's overflow tank and the radiator fan motor does not activate.

The Basics of the Radiator Fan Relay

Your Civic's radiator fan motor relay is located in the under-hood fuse box. So that you can find its location (in the under-hood fuse box), I've painted it neon green in the illustration above.

The under-hood fuse box is located towards the rear of the engine compartment.

If you remove the radiator fan motor relay, you'll notice that its socket (in the under-hood fuse box) has four female terminals. Each terminal provides a specific signal

Since we're gonna' be testing these radiator fan relay circuits (in the under-hood fuse box), here's a brief description of each:

  1. Circuit labeled with the number 1.
    1. Connects directly to the radiator fan motor BLU wire.
    2. This circuit delivers battery power to the radiator fan motor when the relay activates.
  2. Circuit labeled with the number 2.
    1. This female terminal gets power from the #4 fuse of the under-hood fuse box.
    2. Image 2 of 2 shows you the location of fuse #4.
    3. Fuse #4, of the under-hood fuse box, is a 20 amp fuse.
  3. Circuit labeled with the number 3.
    1. Provides battery power for the radiator fan relay's coil.
    2. This female terminal gets power from the #14 fuse of the under-dash fuse box (inside your Honda Civic).
    3. Battery power is only available (at this terminal) with the key in the On position (position II).
    4. Image below identifies the location of fuse #14 of the under-dash fuse box.
  4. Circuit labeled with the number 4.
    1. This terminal provides the ground the relay's coil needs to activate and close the controlled circuit.
    2. This terminal connects to the radiator fan switch (on the thermostat housing) and the PCM.
Location Of Fuse #14 In The Under-Dash Fuse Box. How to Test Radiator Fan Motor Relay (2001-2005 1.7L Honda Civic)

START HERE: The Radiator Fan Motor Relay Tests

There are four separate tests in this tutorial and each one is designed to take the complete novice through the entire troubleshooting experience in a step-by-step way.

Depending on your level of wrenching/diagnosing experience... you can apply the tests to fit your particular situation, or start from TEST 1.

Here's a brief description of each.

  1. Checking the Radiator Fan Relay Power Circuits.
    1. We'll remove the radiator fan relay from the under-hood fuse box and check that circuits 1 and 3 have power.
    2. TEST 1: Checking the Radiator Fan Relay Power Circuits.
  2. Bypassing the Radiator Fan Relay.
    1. After confirming that the radiator fan relay is getting juice (TEST 1), the next step is to jumper circuits 1 and 2 with a jumper wire to see if the radiator fan motor comes on.
    2. TEST 2: Bypassing the Radiator Fan Relay.
  3. Bypassing the Radiator Fan Switch.
    1. Here we're gonna' bypass the radiator fan switch with a jumper wire and see if the radiator fan motor comes on.
    2. TEST 3: Bypassing the Radiator Fan Switch.
  4. Bench Testing the Radiator Fan Relay.
    1. This last test is optional and shows you how to bench test the fan motor relay.
    2. TEST 4: Bench Testing the Radiator Fan Relay.