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

Testing the radiator fan motor on your Honda Civic, to see if it's bad and causing your Civic to overheat, is not difficult.

There are several ways of testing the radiator fan motor. In this tutorial I will show you two different ways to do it.

One way is by bypassing the entire electrical system that controls the radiator fan motor and applying battery power and ground to the fan motor.

The other is taking advantage of the circuits that feed the fan battery power and ground.

Don't worry, it's easier than you think and I'll show you in a step by step way.

Here are the contents of this tutorial at a glance:

  1. Symptoms of a Bad Radiator Fan Motor.
  2. Honda Civic Radiator Fan Motor Basics.
  3. TEST 1: Applying Power and Ground to the Radiator Fan Motor.
  4. TEST 2: Bypassing the Radiator Fan Switch.
  5. Jumper Wire With Alligator Clips With Rubber Insulating Protectors.
  6. Where to Buy the Radiator Fan Motor and Save.
  7. More Honda Civic Test Tutorials.

NOTE: This tutorial on how to test the radiator fan motor complements this one: Radiator Fan Relay Test (2001-2005 1.7L Honda Civic).

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

Symptoms of a Bad Radiator Fan Motor

As you're probably already aware, the radiator fan motor is one of the principal components that helps cool the engine down.

When this bad boy fails on your Honda Civic, the most obvious symptom the engine is gonna' experience is overheating.

You may also see one or more of the following:

  1. Your temperature gauge will max out (as you're driving around).
  2. Your Honda 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.

NOTE: An overheating engine runs the risk of blowing its head gasket, so if your Honda is overheating, you should park it and get the problem diagnosed and repaired.

Honda Civic Radiator Fan Motor Basics

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

Your Honda Civic comes equipped with 2 fan motors. One of them is the AC condenser fan motor and the other is the radiator fan motor.

The one on the passenger side of the engine compartment, nearest to the battery, is the radiator fan motor and the one on the driver side is the condenser fan motor (see photo in the image viewer).

The radiator fan motor is controlled by the PCM and a radiator fan switch.

Here are some more specifics:

  1. The fan motor is controlled by the following important components.
    1. Radiator fan motor relay.
    2. Radiator fan switch.
    3. Fuses (both in the under hood fuse box and in-dash fuse box).
    4. PCM (Powertrain Control Module = fuel injection computer).
  2. The radiator fan switch closes above 199°F (93°C).
    1. This means that the radiator fan switch turns on the radiator fan relay... which in turns activates the radiator fan motor.
  3. When you turn on the A/C.
    1. Both fans are activated and run continuously until the A/C is turned off since the PCM bypasses the radiator fan switch.

Alright, let's get testing...

TEST 1: Applying Power
And Ground To The Radiator Fan Motor

Applying Power And Ground To The Radiator Fan Motor. How to Test Radiator Fan Motor Relay (2001-2005 1.7L Honda Civic)

The most basic test, and probably the most accurate, is manually adding battery power and chassis ground to the fan motor.

The accuracy of this test lies in the fact that it bypasses all of the fan motor's control components and circuitry and let's us know without a shadow of a doubt if the fan motor is good or not.

In case you're wondering, the components we're bypassing are: radiator fan relay, radiator fan switch, and the fuses.

IMPORTANT: This test should be done with your Honda Civic's engine completely cold or you run the risk of getting burned by the radiator or the engine's hot surfaces!

OK, this is what you need to do:

  1. 1

    Unplug the radiator fan motor from its connector. The fan motor that you're testing is the one that is nearest to the battery (fan motor on the passenger side).

    NOTE: All of the test connections will be done to the radiator fan motor's connector and not the engine's wiring harness connector.

  2. 2

    Apply ground to the connector terminal labeled with the number 1 (in the illustration in the image viewer), using a jumper wire connected to the battery negative (-) post. Terminal number 1 connects to the fan motor's BLK (black) wire.

    NOTE: If you haven't already, please read the section: Jumper Wire With Alligator Clips With Rubber Insulating Protectors.

  3. 3

    Apply power (12 volts) to the connector terminal labeled with the number 2, using a jumper wire. Terminal number 2 connects to the BLU (blue) wire of the fan motor.

    IMPORTANT: Be careful and don't touch this ‘power’ jumper wire to any metal surface on your Honda... or you'll short circuit the jumper wire!

  4. 4

    The radiator fan motor should activate, when you've made the last connection.

    Let's take a look at your specific test results below.

CASE 1: The radiator fan motor came on. This test result tells you that the radiator fan motor is good.

Since the fan motor isn't activating on its own... the next step is to check the radiator fan motor switch. For this test, go to: TEST 2: Bypassing the Radiator Fan Motor Switch.

CASE 2: The radiator fan motor DID NOT come on. Double check your test connections and repeat the test once again.

If the fan motor still does not activate, then you've confirmed that the radiator fan motor is fried and needs to be replaced.

If you need to buy the fan motor, check our my suggestion on where to buy it here: Where to Buy the Radiator Fan Motor and Save.