Test if Fan Works?

[L84THSKY]

Did some more troubleshooting. First off, the voltages to both the low speed and high speed relays are there. That is both the triggering voltage, and the main voltage. The high speed relay, in the "un-energized" state passes the voltage to the low speed relay. I pulled out the low speed relay, and put a jumper between pins 6 & 2 (see diagram), and the low speed fan came on. That means the entire fan assembly is good. This was done while I also had a jumper in the temp sensor low speed pins 2 & GND.

Hopefully, that would point to the low speed relay being the problem. When I swapped the AC fan relay, and the low speed relay, the fan did not come on. So either both the fan relay is bad & the low speed relay, or it is not the relay.

I did turn on the A/C, and the high speed fan came on. That would imply the A/C fan relay is good.

Looking at the diagram, it appears the DME sits between the path of the double temperature switch and the actuating function of the low speed relay. This is not the case for the high speed relay, and explains why when I jumper ed pins 1 & GND of the temp switch, the high speed fan came on.

So I can force a connection across pins 2 & 6 of the low speed relay, but I can't get the GND from the DME to actuate the low speed relay properly.

Again, that assumes the relay isn't bad. I only hope the relay IS bad, that would be an easy fix. If not, I must trace the path from pin 2 of the temp switch, through pin 68 of the DME, then out pin 57, and finally to pin 5 of the low speed relay.

Can I get the low speed relay at a parts store, or only at the dealership?

Any thoughts?

Originally Posted by JNCoulombe

If you tried swaping the low speed relay and the low speed still didn't work when you used a paper clip to jumper around the fan switch (as described by campaiar) the fan switch (temperature sensor) is probably not the problem. The next obvious thing to check is the continuity of the fan low speed resister mounted on the back of the fan.

[JNCoulombe]

My mechanic had mentioned that he thought that even with jumping the fan switch leads for the low speed fan to come on the engine would have to be hot. I don't know what the DME is doing with the input from the radiator switch but perhaps it is integrating another temperature input. Is the engine hot when you are doing your trouble shooting?

[L84THSKY]

No the engine was not hot. Maybe that is why the relay didn't actuate. I still wanna replace the relay, then I'll try warming up the engine.

Originally Posted by JNCoulombe

My mechanic had mentioned that he thought that even with jumping the fan switch leads for the low speed fan to come on the engine would have to be hot. I don't know what the DME is doing with the input from the radiator switch but perhaps it is integrating another temperature input. Is the engine hot when you are doing your trouble shooting?

[Petex]

Related problem:

Summer is at last coming here in Finland. Yesterday I noticed at trafficlights that
engine is warming up a little too much.
I stopped and noticed that I have the double temperature switch at its place, but theres no wire attached?!?

Front end of the car has been rebuilt last autumn. I think mechanic has forgot that wire and cant find it.

Would someone do me a favor, and give me a hint where I should look for it.
I know it comes from DME, but where is that

Thanks!

[Bobbak]

behind the battery is the dme you gotta pull back some foam and you will see the box

[JNCoulombe]

With any luck your mechanic put the the wiring harness for the radiatior switch back into place and you won't have to run wires from the DME. The harness should be present under the top brace in front of the radiator and appears to run across the front of the car. It then runs down into the engine compartment with the connector for the radiator switch comming off about 20 cm to the left of the radiator switch and the remainder running down to a connection on a part of the air conditioner. Good luck.

[L84THSKY]

I drove to work yesterday, got stuck in traffic. Temp gauge was climbing, went past the 3/4 point, but not into the red. Traffic started moving, and it calmed down. Can't be sure if the fan came on, sounded like it was but hard to hear.

After testing my system previously, it looks like the fan (high and low) and relays are good. I'm beginning to wonder if the radiator sensor is the problem. I have a new one, will put it in this weekend. I'm hoping the sensor is just not actuating at the correct temperature.

Originally Posted by JNCoulombe

My mechanic had mentioned that he thought that even with jumping the fan switch leads for the low speed fan to come on the engine would have to be hot. I don't know what the DME is doing with the input from the radiator switch but perhaps it is integrating another temperature input. Is the engine hot when you are doing your trouble shooting?

[JNCoulombe]

The radiator switch is the first thing to check. It is also important to be sure the system is "burped" so that the switch sensor end is actually in contact with the radiator coolant. You should be able to see if the switch has closed when the engine is hot with an volt/ohm meter or even just a 12V lightblub and some wire.
One caution, I had a local shop replace mine and even though the temperature specs were appropriate (there are two temperature range switches available, mine needed the lower opening variant) the switch they got from their supplier did not open at the specified temperature and was far too slow in opening. If the system otherwise checks out but still doesn't work after you've replaced the radiator switch, it isn't a bad idea to test the replacement in a pan of heated water.
Another tip, If you are overheating in traffic because the low speed fan isn't coming on, turning on the airconditioner should force the high speed fan to come on and the engine should cool down.
However, I thought that you already determined that the fan wouldn't run when you shorted between the switch leads and ground (blk/grn or blk/gry and brn switch connector wires in the diagram above). If the fan won't run when the switch is shorted closed then replacing the switch won't work either.

[gimp]

^^^ air trapped in the system was my problem, with your exact same symptoms (overheating only in traffic, etc)

[L84THSKY]

As you mentioned earlier, the car must be hot in temperature to turn the fan on. Shorting the connector won't trigger the low speed fan unless the car is hot. But even if it is hot, maybe the radiator switch sensor is bad. Or, as someone just mentioned, there is air in the system.

What is the part# of the sensor that turns on at a lower temperature? What are both part#'s, and what are the temp ranges?

Originally Posted by JNCoulombe

However, I thought that you already determined that the fan wouldn't run when you shorted between the switch leads and ground (blk/grn or blk/gry and brn switch connector wires in the diagram above). If the fan won't run when the switch is shorted closed then replacing the switch won't work either.

[L84THSKY]

How do I burp the system? I know there is a bleeder valve on the side where the fluid level is measured. I was thinking along those lines today. What if the fluid isn't hitting the sensor. The level rises as the car pressurizes, and it still may not be hitting the sensor.

Originally Posted by gimp

^^^ air trapped in the system was my problem, with your exact same symptoms (overheating only in traffic, etc)

[JNCoulombe]

Burping the system is accomplished by removing the bleed screw on the top of the radiator then adding coolant to the overflow reservoir until coolant free of bubbles comes up through the bleed screw orifice. Do this once, drive the car until warm. Let it cool down and repeat Sometimes it takes several tries to completely bleed the system.
The radiator switch is a dual switch and there are two types with different temp ranges. The temperature range is engraved on the switch. I think the part number for the low range switch (80/88 degrees C) is 61 31 8 361 787.

[L84THSKY]

I just did as you described, and the Bentley manual describes it as well. No fluid started coming out of the bleeder valve, even after I fill the reservoir almost to the top. I closed the cap and valve, and drove it around the block. Then I let it cool for a bit, and loosened the bleeder valve. Some air came out, but not much. When I opened the cap, the level had gone down, just below the cold line. I added some more fluid, got it up to temp, and then bled the valve. Gonna take on the highway and hope it's resolved.

Not sure if I'm gonna replace the temp switch on the radiator this weekend, since I would like to know if the bleeding fixed the problem.

Originally Posted by JNCoulombe

Burping the system is accomplished by removing the bleed screw on the top of the radiator then adding coolant to the overflow reservoir until coolant free of bubbles comes up through the bleed screw orifice. Do this once, drive the car until warm. Let it cool down and repeat Sometimes it takes several tries to completely bleed the system.
The radiator switch is a dual switch and there are two types with different temp ranges. The temperature range is engraved on the switch. I think the part number for the low range switch (80/88 degrees C) is 61 31 8 361 787.

[b.u.ti-ful]

My car overheated and some checking shows that the fan is not working.

My 1996 has a two speed electric fan and when I jumper the sensor on the side of the radiator I can get the high speed to run, but not the low speed.

The relays are good (swap) and I am inclined to think it is the low speed resistor mounted on the fan.

Problem is I don't know how to test the resistor and Bavauto does not sell one for 318ti.

Anybody know about these resistors?

[b.u.ti-ful]

Here's the bad-boy I'm talking about: