Cooling Fan Test Proecdure and FAQ

Last updated: October 16, 1998

Date: Wed, 14 Oct 1998 08:30:08 -0400
From: "Houseman, Carl W. x1323"

[Note to all: this is the most comprehensive FAQ I've written yet on the 3rd gen fans. If I've left anything out or stated anything incorrectly, please advise.]

Wiring and Fan Motor Test:

For the following two tests the engine is not running, car is cold, ignition on and A/C switch off:

  1. Ground the TFA terminal in the diagnostic connector. Do the fans run? That should be "low" speed. If the fans don't come on at this speed during normal operation it could be an ECU or temp sensor problem.

  2. Remove the ground from TFA and locate the fan circuit test lead by the ECU in the passenger footwell kick panel (black/yellow-stripe wire not connected to anything). Ground it. Wait 2 minutes and the fans should come on. This is "medium" speed. If the fans never run at this speed in normal operation it could be a problem with the 226F coolant switch (different from the temp sensor).

    [If you can't find the fan circuit test lead near the ECU, you may not have the coolant recall fan modifications.]

  3. Now repeat tests 1 and 2 with the A/C switch engaged and blower motor at speed 1. Fans should come on immediately at low with A/C switch engaged. You'll then hear medium for test 1 and high speed for test 2.

    If the fans don't run under the test conditions above then there's a relay or wiring problem.

Operational Test:

[Note/disclaimer: run the following test at your own risk. I am not responsible for overheating your engine! See WARNING note at the end.]

Start the engine and let it idle with A/C off and watch the temp gauge. Within 5-10 minutes after reaching operating temperature on the temp gauge, the fans should come on at the same low speed you heard at the first test 1. If not, or if the fans come on eventually at medium speed, there is a problem with the engine temp sensor or ECU.

WARNING: If you see the temp gauge start to go up after it stays at the "middle" point for a long time, either turn on the A/C to get the fans running - assuming that works - or shut off the engine immediately. Neither of your temp sensors are working or the ECU is unable to control the fans. If the temp gauge doesn't go down immediately after the A/C fans come on, shut off the engine immediately then turn on the ignition to keep the A/C fans running.


Q: My fans are running, then I shut off the engine and they don't keep running. Why not?

A: The coolant recall fan mods must be installed and the 226F coolant temp switch must sense high coolant temp for 2 minutes or more at the time of key-off in order to keep the fans running. For this to happen naturally _generally_ requires running the car hard in hot weather followed by an immediate shutdown (without any cooldown period).

Q: How can I tell if the coolant recall fan mods have been done?

A: Look for the black/yellow-stripe wire near the ECU, not connected to anything. Then run test 2 above. If you can't find the wire, the mods are probably not done or not done correctly.

Q: When the fans stay on after ignition off, how long do they run?

A: 10 minutes.

Q: When I shut the engine off, the fans were not running. Shortly after that I turned the ignition on but didn't start the car and the fans came on. Why?

A: The fan circuitry works the same whether the engine is running or not, when the ignition switch is on. After you turn the engine off, coolant stops circulating. Without circulation, it heats up to the point of tripping the temperature sensors that run the fans. So when you turn on the ignition, the sensors say "run the fans" and the ECU complies.

Q: Why do the cooling fans come on when turning on (a) the headlights, (b) the fan blower to position 3 or 4, (c) the parking lights, (d) as a result of other electrical loads.

A: This seems to be a designed-in anomaly in the 93s and possibly some early 94's. At some point the 94 models stopped coming with this feature and I suppose no 95's do this. It makes no sense to turn on the fans due to a high electrical load.

Q: Where can I get the wiring diagrams for the fans?

A: The post-coolant-recall diagrams are online at (this site, go to How-to --> Cooling System --> Fan Circuit (Post-Fuel-Recall)).

Q: How can I get the fans to run after shutdown even if the coolant recall circuitry doesn't require it?

A: Go to How-to --> Cooling System --> Cooling Fan Modification.

Q: Do both fans run at once or does one fan run for low speed and the 2nd fan come on for higher speeds?

A: Both fans run at the same time, and the same speeds, always. They are wired in parallel.

Q: Why does one fan have 5 blades and the other 4?

A: Mazda wanted us to waste time discussing such trivia. Perhaps it has something to do with greater airflow on one side of the radiator vs. the other, but how much difference it makes has got to be minimal... certainly not worth the tooling costs for two different parts IMHO.


Date: Wed, 14 Oct 1998 09:47:32 -0500
From: tom

The fans have different numbers of blades to reduce odd noises that would result from the "beats" that would occur when the frequencies of 2 fans with the same number of blades got really close and then varied a bit, kind of like when tuning a guitar.

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