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

In this tutorial, I'm gonna' show you how to test the fan relay and, more importantly, how to test the radiator fan relay's circuits in the under-hood fuse box.

The results of your tests will help you troubleshoot the reason your Honda Accord's radiator fan motor isn't working.

Although this info applies to any 1998-2001 4 cylinder Honda Accord, the basic testing procedure (in each test step) can by applied to any Honda.

Since in this tutorial we're only troubleshooting the fan relay and its circuits, you'll find the radiator fan motor test here: How To Test The Radiator Fan Motor (Honda 2.2L, 2.3L).

Symptoms Of A Bad Radiator Fan Relay

If the radiator fan motor relay fails, the most obvious symptom that your Honda Accord will experience is overheating due to radiator fan not coming on.

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

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

The Basics Of The Radiator Fan Relay

The radiator fan relay is located in the under-hood fuse box (see the illustrations in the image viewer).

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

The radiator fan relay 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.
   • Battery power for the radiator fan motor.
   • Power provided by fuse #57 (20 Amp) of the under-hood fuse box (see image 3 of 4).
   • Hot (+) all of the time.
2. Circuit labeled with the number 2.
   • Circuit that channels the battery power to the radiator fan motor when the relay closes.
3. Circuit labeled with the number 3.
   • Battery power for the radiator fan relay's coil.
   • Power provided by fuse #4 (7.5 Amp) of the left side dash fuse box (see image 4 of 4).
   • Hot (+) only with Key On Engine Off (KOEO) or Key On Engine Running (KOER).
4. Circuit labeled with the number 4.
   • Circuit that feeds the radiator fan switch's ‘On’ or ‘Off’ signal to the radiator fan relay.

OK, let's get testing.

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