Have replaced the FCM twice. First one caught fire within about an hour. put it out, replaced burnt harness, and tried a new one. Fans still running. Checked the temp sensor and it appears to work. Car will reach proper temp while running and stop midway where it usually does. Coolant full, water pump and thermostat appear fine. I am getting 12 volts at the white wire on the FCM even when turned off, so I guess it is the ECM? Car seems to run fine now, but fans always at top speed and won't cut off when I turn ignition off.

 

Keleb, just because you turn off the car does not mean that the fans are going to turn off. If you park the car and then wait outside of it for a minute or so, some cars will run their fan because of the hot motor heating up the water just a little more and it making its way to the sensor. Having a fun run for a minute or so after the car is turned off I would consider normal. Now, with that being said, could you have an issue with your thermostat that is causing the motor to run a little warmer (a few degrees), of course. So, a good flush and a new thermostat may be in order. If the fans only go between off and fast, then you have a different issue. That would be your second fan controller is on its way out.

 

That main culprit

 

Even when the engine is cold overnight when i connect the battery it immediately runs

 

If the fans start as soon as you connect the battery (with a cold engine), then you have a bad fan controller. The only other possibility would be a shorted wire that is putting 12 VDC on the speed control line. We have experienced where you buy the cheap controller that is the "jaguar replacement part" that they fail almost immediately upon install just like you say you are seeing. What you are describing sounds a lot like a transistor pair that has failed that is causing the fans to see power all the time.

 

Keleb, you should have 2 white wires going to the fan controller. If you look closer, one will have a blue stripe on it, the other will have a green stripe on it. The one with the blue stripe should have no voltage on it unless the motor is up at temp. The one with the green stripe is coming off of the switchable 12 VDC source of the car. So, it may have 12 VDC on it. Both of these wires should be in the same harness and plug assembly.

 

I don't have an ammeter or voltmeter to measure stuff so. It gonna be hard for to determine that.
Thanks was planning to taking the fan module apart and see what wrong. These transistor can't be replaced?

 

Keleb, what I would say then to do is to disconnect the 3 wire plug going into the fan controller that has the 2 white wires on it. Locate the white wire with a blue stripe. If you look at the plug, there should be a way to remove the wire (may need to take off the back of the plug, especially if it has a red plastic piece there). From there, you should see a small retaining tab on the silver tab attached to the end of the wire. Depress that tab and pull the wire from the plug. tape it up . Put the plug back together and plug it in and connect up the battery. May even want to start the car for a few minutes. If the fans run at this point, then this confirms a bad fan module. If they don't run initially, you can "force" them on by turning on the A/C to your car with the temp dialed to the lowest temp and the fan speed set to max. If the fans still do not come on, then this confirms that your ECU is the source of your problem. Reinstall wire once you know where your problem lies and put the car in a safe state.

As for replacing the transistors in the controller, yes, they can be replaced. The trick will be getting the new transistors. These are not something that you go to our local hardware store and they are going to have sitting on a shelf. Most electronic stores will not carry them. You are going to have to do some searching to find them online. As for what to buy, if you look on the transistors, you should see some white writing. Normally the middle lettering is the part number to the transistors. Keep in mind that not all of the parts use the same transistors. You will most likely find the 3 of them are one part number, the other 3 are a different part number. Then you will need to make sure that the transistors have the proper heat sink paste attached to them to help them cool against the heat sink (this is where the cheap controllers are making the mistake or not even installing a heat sink). If you need more information, let me know. There is a lot of stuff that will look very similar, but it is dramatically different. This is where knowing electronics and what all the numbers mean is essential.

 

I shall do that and get back to you Sir
Very soon

 

I have done just that, removed the blue and white wire, tapped it, reconnected the fan cable nd battery, it immediately ran. So thus confirms the module is damaged.
I will have to get a new one after lock down. Thanks a lot, you a indeed the best sir. In the meantime i will open and have a look at the module internally. If i had the expertise i would fix the transistors and reconnect.

 

Everything looks mint, not burnt areas. The paste is not that much.

 

Keleb, see that dark green board hidden under the silver plate, that is where you need to look. That is where the transistors are. You may find that they will show signs of heat damage. But, odds are, it will be in your best interest just to get a new module (do not buy the cheapo chinese ones, spend the extra to get a real controller. The factory fans are current mongers. They each pull something like 40-50 amps. That is really hard on the electronics. hence why the controllers fail a lot.

 

keleb, I looked up the part number. That should be a good unit to buy. I guess I have to ask "when did you buy it?". If you just bought it and installed it, then it should have a warrantee on it and you should be able to get a new unit. If you have had it installed for a few years. probably not. if you got a few years out of it, then odds are that was about its life. I have seen people have to replace these every few years. This is especially true if you like to run the A/C at full blast to keep the inside of the car ice cold (this makes the fans run at max speed and therefore fries the electronics).

 

I shall find a replacement, it was the first time since 2007. So it haa reached it's life. Thanks a lot. I will use it to learn