Mazda Fan Starts With Accelerator

[simpleone]

Friends.

My car is Mazda Familia BJ5P. Whenever I accelerate, both the radiator fan and the AC fan start. This happens even before the coolant temperature reaches fan starting point. I got a person to remove and check the alternator since he said it could be the alternator IC. Replaced the IC but still I'm seeing the issue. Anyone can think of a reason? Or is this normal?

Thanks

[The Don]

Friends.

My car is Mazda Familia BJ5P. Whenever I accelerate, both the radiator fan and the AC fan start. This happens even before the coolant temperature reaches fan starting point. I got a person to remove and check the alternator since he said it could be the alternator IC. Replaced the IC but still I'm seeing the issue. Anyone can think of a reason? Or is this normal?

Thanks

On the BJ5P if I'm not mistaken the fan circuit is operated by the thermostat only when the AC is not on. The work is run by one relay which on default position is energised by the thermostat and as soon as the thermostat breaks the signal it turns the radiator fan on. You can test this function by checking if the fan turns on when you move the ignition key to on position, and then pulling the connector out of the thermostat and the fan should start instantly.

This function is overriden when the AC is on where both the radiator fan and the condenser fan is turned on with the AC switched on.

If the fan comes on randomly, you need to check the relay and the wiring to the relay.

[simpleone]

Thanks. I also think something must be wrong with relay. And the same electrician guy told me to get the ECU scanned since most of the Mazda functions run through ECU. I will get both checked and post if there is any update.

[Rumesh88]

Thanks. I also think something must be wrong with relay. And the same electrician guy told me to get the ECU scanned since most of the Mazda functions run through ECU. I will get both checked and post if there is any update.

Do they (both fans) start in the same manner that you have explained soon after a cold start (ie like when you start the car first time in the morning) with AC switched off? or is it when the temperature gauge pass beyond 1/4 mark or so? Has anyone meddled with the AC/dashboard or nearby wiring? In addition to this did you have any issue with battery charging recently? It is unlikely you would find a fault even if you do a ECU scan, unless you get at least an intermittent CEL indication.

[simpleone]

Do they (both fans) start in the same manner that you have explained soon after a cold start (ie like when you start the car first time in the morning) with AC switched off? or is it when the temperature gauge pass beyond 1/4 mark or so? Has anyone meddled with the AC/dashboard or nearby wiring? In addition to this did you have any issue with battery charging recently? It is unlikely you would find a fault even if you do a ECU scan, unless you get at least an intermittent CEL indication.

Both fans start as soon as the accelerator is pressed even in the morning cold start with AC off. I'm not sure whether the previous owner has done something to the wiring but he has not treated the car well for a fact. I didn't notice any battery charging problem and the voltage is in optimum levels as per the battery guys.

However when both the fans start, other electricals like the lights and fans go dim for a split second to negotiate the sudden draw of power.

[Rumesh88]

Both fans start as soon as the accelerator is pressed even in the morning cold start with AC off. I'm not sure whether the previous owner has done something to the wiring but he has not treated the car well for a fact. I didn't notice any battery charging problem and the voltage is in optimum levels as per the battery guys.

However when both the fans start, other electricals like the lights and fans go dim for a split second to negotiate the sudden draw of power.

To me it looks like someone has done a modification to overcome/bypass some other issue (like overheating for example) though it is not a final conclusion. For ECU to start both fans, it must detect an AC switched on condition like The Don said above. Get an auto-electrician just to check if the wiring has been modified in someway.

[simpleone]

To me it looks like someone has done a modification to overcome/bypass some other issue (like overheating for example) though it is not a final conclusion. For ECU to start both fans, it must detect an AC switched on condition like The Don said above. Get an auto-electrician just to check if the wiring has been modified in someway.

I will do a check and update this thread. Probably it will take a couple of weeks to get a free day to do so. Fuse box is the place to start I beleive.

[simpleone]

Update: Got the ECU checked and the person said it is different than what originally comes to the model. I need to take the car to him again some other day for a full check since he was bit busy that day.

[The Don]

Update: Got the ECU checked and the person said it is different than what originally comes to the model. I need to take the car to him again some other day for a full check since he was bit busy that day.

When somebody says something like this, always get a second opinion before you do anything.

Also ask him for the original ECU part number vs the ECU part number that is actually installed.

[simpleone]

When somebody says something like this, always get a second opinion before you do anything.

Also ask him for the original ECU part number vs the ECU part number that is actually installed.

Agreed. Even previously I trusted the guy when he said alternator IC should be replaced. He burnt one in the very minute and got another one. Second one gave the same results of the original one before replacement. (aiyo salli)

Edited January 7, 2015 by simpleone

[Davy]

Agreed. Even previously I trusted the guy when he said alternator IC should be replaced. He burnt one in the very minute and got another one. Second one gave the same results of the original one before replacement. (aiyo salli)

Shouldn't have trusted the same guy with your ECU when he couldn't even work on an alternator carefully.

Anyway, do the fans come on even when the accelerator is slightly pressed? Or do you have to rev a bit hard to get them to turn on? Why I'm asking is because when the brushes wear out, the fans need a small push to get going. When you rev hard, the vibration might move the fan a position where the armature makes contact with the brush and starts working.

But for this to happen, both the fans should have been wired directly (which is wrong) + both should have worn out brushes. Slim chance, yet a possibility. To check if this is the case, you can start the car and manually rotate the fan blades to see if they start working (be extremely careful).