cooling fan problem (please see the bold font especially)

[dudemaaan]

well yesterday a couple wires somehow shorted out at the front harness near my passenger headlight. I got the wires repaired, one was a large blue wire the other a brown/white wire and the 3rd was a green/yellow wire.

Afterwards my fans wouldnt come on with the Power FC settings. They would come on immediately if i turned the A/C switch on, and ive been running them this way to keep the engine cool. The 4th relay that looks different then the other 3 i believe is the one that is controlled by the A/C switch its working fine.

I was trying to test the other relays and they appeared to be working at first, at least 2 of the 3. Then i got a little confused as to which was which and then they all seemed like they checked out, then i dont know if i did something but none of the 3 seemed like they were working correctly after that. So maybe i messed them up or something.

I'm going to try to get new relays but i need to know a couple things after i get them.

One of the relays has a Large black wire, after putting a voltmeter on it, i discovered this black wire is a ground, or is grounding out. I dont know which is the case, so i need to know is this wire supposed to be grounded or supposed to have positve voltage?

Reading the workshop manual it said to apply voltage to relay terminals C and D then check continuity between a- b. Well my black wire is on terminal D and its grounded out, so if i connect power to this wire it just get sparks. (thats how i found out it was grounded, i then did a continuity test between it and ground to verify)

I would like to test to make sure the ECU is sending the signal to turn the fans on. I will set the fans to 0 and then test whichever wire(s) i need to. On the ECU what wire(s) is this and at the relays which wire/wires is this?
_________

[scotty305]

Here is a diagram that should be more intuitive. The solid lines should be +12V and the broken lines should be 0V (ground).








Relay No.1 is only controlled by the 'Heater Control Unit,' which is the A/C and fan control switch on the dash. Relay 1 is only powered when the Ignition switch is on, it cannot run after the car is shut off.

Relays No.2 and No.4 are peforming the exact same function. Think of them as one relay. Connecting the dashed green line to ground will turn the relays on, which will give power to both fans. There are a few different things that can enable these relays, including the Data Link Connector, ECU pin 3D, and the Coolant Fan Control Module on post-recall cars. Relays 2 and 4 are always powered by the battery, they can activate the car even when the key is not in the ignition.

Relay No.3 switches a second ground to both fans. This will change the speed from low>> medium or from med>> high. Relay 3 is always powered by the battery, it can increase the fan speed even when the key is not in the ignition. The line that I marked with dotted pink is going to be ground when the solenoid is on. When you measure it, you should be seeing 0V on your multimeter when the relay is switched on. You might never see 12V on this wire during normal operation





Here's a table showing how the relays work together to control the fan speed:



To turn a relay on, ground the signal wire (bottom-left on each relay in the diagram). For instance, to turn on Relay No.1, connect the thin Violet/Pink wire to ground. I used a piece of stereo wire, connected to the negative battery terminal. You'll hear a click when the relay turns off or on. Relays No.2 & No.4 are activated with a thin Green/Black wire, and relay No.3 turns on with the thin Blue/Green wire. Remember that most of the relays can activate the fans even if the key is not in the ignition.

-s-

[dudemaaan]

thanks for that diagram, i had found a very similar diagram in the fsm, or one of the mazda wiring books. I traced everything back and marked the relays (1,2,3,4). i found my relays are definitely bad.

I managed to figure out answers to most all my questions except,
i discovered the relays controlled by the ECU, (2 and 4) the green and black wires that get the signal from the ECU (i believe they first go to the blue connector in the kickpanel) are turning the voltage on and off with the PFC like normal, but its only 5 volts, not 12 volts, is this normal? This is how i tested them.

I unplugged the relays to test the wires individually. I set the PFC to 0 for temperature then put a multimeter on the G/B wire of relay 2 and 4. got a positive 5 volts. Turned the temperature back up to 100 on PFC tested wires again 0 volts just like it should.

I expected that the voltage would be 12v, but i know alot of signals the ecu sends and receives are actually 5 v so maybe its normal?

[dudemaaan]

Here is the diagram i found. If you notice my diagram shows section 30 for the G/B wires of relays 2 & 4,(see the circled number right next to the left fan) the other diagram posted above shows section 29. When i went to find section 30 it was for something else, but right next to section 30 was section 29 which showed the cooling fan relays. So Whoever made my diagram (mazda?) had an error in this diagram. I thought that was odd.

[dudemaaan]

ok well i got the relays in, and my problem is still there. i tested the relays and they all work. i discovered my old ones were working too. all but one of them anyways.

The problem seems to be the ECU is not grounding out the GREEN/Black wires on relays 2 and 4. What could the problem be?

If i unplug the relays, the green/black wires on relays 2 and 4 will receive power from the ECU 5v's positive voltage when i set the power fc to turn the fans on at 0. if i set them to a higher temperature then what the water temp is the voltage goes to 0. I'm under the impression that it's supposed to ground out the G/B wire, so why am i seeing 5v positive?

[dudemaaan]

ok i tested at my ecu and found that pin 3d is not grounding out at the ECU. the ecu still displays the temperature of the water on my datalogit. DO the fans use the same sensor or is it a different one? Im trying to narrow down if its my ECU or a thermo sensor that tells the ecu when to ground out. There is also mention of the powertrain module or something what does it do in all of this?

[Chadwick]

If your car has had the cooling TSB done, look for an extra grounding strap coming from the black box’s wiring harness behind the ECU. A lot of people fail to hook this up when they swap out the computer. Don't confuse it for the black and yellow wire that has a spade connector, which is a constant 12v wire.

Dan

[dudemaaan]

yes thats hooked up

[scotty305]

The ECU only uses one sensor to measure water temp, if it is displaying temperature properly then it should know when to activate the fans. Does the PFC have some sort of parameter in the software to tell you it is trying to activate the cooling fan?

It sounds like there could be one of three things wrong:

1.) Relay doesn't work properly.
2.) Relay is not wired properly to power, signal, or to the ECU (which will be GND when activated). You should be able to measure +12V on the wires I've outlined in solid colors, or 0V on the wires I've outlined in dashed colors.
3.) Something inside the ECU is damaged and it isn't able to ground the relay properly.


By the way, I'm not a PFC expert but I don't think you should see +5V on the G/B wire. It should be about 12V or 0V. If your car will run OK with the stock ECU, maybe you should try that and see if it activates the fan. If not, see if you can get ahold of a friend's PFC or try your PFC in another car to see if things work differently with that car's wiring and/or relays.

[dudemaaan]

yeah i think the PFC must have something damaged that controls the fans.
i'm using a variable thermostat to control relays 2/4 now. I just wired it into the stock relays. Works well