TEST 1: Applying Power And Ground To The Radiator Fan Motor
The first thing we'll do is apply power (12 volts) and ground to the radiator fan motor and bypass the radiator's control circuits (these are: radiator fan relay, radiator fan switch, and the fuses).
By directly applying power and ground to the radiator fan motor, we'll be able to eliminate the fan motor as bad or not.
IMPORTANT: This test should be done with your Honda'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:
Unplug the radiator fan motor from its connector.
NOTE: All of the test connections will be done to the radiator fan motor's connector and not the engine's wiring harness connector.
Apply ground to the connector terminal labeled with the number 2 (in the illustration in the image viewer), using a jumper wire connected to the battery negative (-) post.
NOTE: If you haven't already, please read the section: Jumper Wire With Alligator Clips With Rubber Insulating Protectors.
Apply power (12 volts) to the connector terminal labeled with the number 1, using a jumper wire.
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!
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.
TEST 2: Bypassing The Radiator Fan Motor Switch
If you've reached this test step, you've confirmed that the fan motor DOES activate when you directly apply power and ground to the radiator fan motor (yet it doesn't activate on its own when your Honda is overheating).
In this test, we're gonna' indirectly test the radiator fan motor switch by bypassing it with a jumper wire.
With this test, we'll able to see if the radiator fan motor switch has failed or not.
This is a very simple test but it does require one very important safety precaution:
PRECAUTION: The engine and the radiator on your Honda must be completely cold to avoid getting burned.
OK, this is what you need to do:
Disconnect the radiator fan motor from its pigtail connector.
Remember: Your Honda's engine should be cold.
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.
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).
The radiator fan motor should activate, as soon as you turn the key to the On position (KOEO).
Let's interpret the test results:
CASE 1: The radiator fan motor came on. This is the normal and expected test result.
This test result tells you several important things:
- The radiator fan motor relay is good (otherwise the fan would not have come on).
- The radiator fan motor and fan motor relay fuses are NOT blown (otherwise the fan would not have come on).
- The wires between the fan switch and radiator fan motor relay are not shorted (otherwise the fan would not have come on).
- The wires between the radiator fan motor and radiator fan motor relay are not shorted (otherwise the fan would not have come on).
Therefore, 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:
- The radiator fan motor.
- The radiator fan motor switch.
Although it's beyond the scope of this particular tutorial... you're next step is to check the radiator fan motor relay. You can find the radiator fan relay test tutorial here: How To Test The Radiator Fan Relay (Honda 2.2L, 2.3L).