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Hi guys, I am new to this forum but not with working on cars. I friend of mine has an 02 MCS and last Saturday the coolant fan started running all the time, even with the ignition off. It would have run until the battery was dead if she had not unplugged the battery. So her boyfriend and I started looking online and we came to the conclusion that the whole fan/shroud assembly must be replaced because several people have had this problem and the solution always seems to be replacement due to faulty resistor.
Jump to last night, I replaced the fan and as soon as we plugged the new unit in the fan started running again, just like the old fan. So my question is, what else controls the operation of the fan. A coolant temp sensor? What else should I be looking at? And where is it located?
It seems that this is a common enough problem and that everybody has resolved it by replacing the fan, is it possible that the new fan was faulty from the get-go? Any other thoughts would be appreciated.
After I reassembled everything I topped off with coolant/distilled water and bled the whole system so it is definitely not low on coolant. Also, the high and low speed on the fan both work, when the car is on and warm the high speed is running, and once you shut the car down it turns to lowspeed and continues to run until you unplug the battery or the fan wire harness
I would guess that the temp sensor is bad. If it's the barometer type the contact has opened and will not close.
Can you tell me where this is located? I have a Bentley Manual for my car, but not for this one. I was looking around for a temp sensor last night but couldn't find anything that screamed temp sensor to me.
Is there any way to check the coolant temp sensor to see if it is bad?
OK. I just got a fax from my brother showing the sensor. But the fax is dark.
It is located on the left side of the engine, [DRIVERS SIDE]. It appears to be located near the trubo intake or air intake. But what I make out better is the shift linkage for the transmission. The sensor is above this linkage.
Thanks, I will try to take a look. Anyway to test this besides replacing with new. I know on Audi's you can measure resistance across two terminals to see if it is within spec.
The temp sensor is on the driver's side end of the head. It is a reverse thermistor, which means that if it is open, (broken wire, disconnected plug, etc) it will read max. hot and turn your fan on. However, it will peg your temp gauge...is this the case? I'd look at the relay in the fuse block under the hood. There are four the same; swap it out with another and see if the problem persists.
The temp sensor is on the driver's side end of the head. It is a reverse thermistor, which means that if it is open, (broken wire, disconnected plug, etc) it will read max. hot and turn your fan on. However, it will peg your temp gauge...is this the case? I'd look at the relay in the fuse block under the hood. There are four the same; swap it out with another and see if the problem persists.
Thanks. I believe the gauge is reading normal. Just so I understand, on a car that is functioning normally you could disconnect the temp sensor with the ignition off, and the fan should come on?
I will check the relays by swapping them around. Thanks for your help.
OK. I just got a fax from my brother showing the sensor. But the fax is dark.
It is located on the left side of the engine, [DRIVERS SIDE]. It appears to be located near the trubo intake or air intake. But what I make out better is the shift linkage for the transmission. The sensor is above this linkage.
Yes. On the 2002 and 2003 it was on the fan assembly. Later it was moved to be more easily replaceable.
Was you new fan "new"? OEM or aftermarket? I am voting for a bad new fan assembly.
Also as I have said before, on Artoo, when the fan occasionally stays on, taping the relay shuts it down. Much easier than changing the assembly.
Rich
Since this isn't my car, I didn't buy the fan assembly. But, I don't think it was OEM. I am going to try a few of the possibilities listed above, but if that doesn't work out I may see if another fan assembly works. Thanks.
There was one thread where a fan not turning off turned out to be caused by a bad computer....ouch!! Not sure what trouble sooting you would have to do to rule that out. Did they get the right fan??
Depending on the year, the relay may or may not be on the fan....on the newer ones it was moved. Not sure what the effect of useing the wrong fan would be, but it just might be the problem that you are seeing.
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Update: I took a few weeks off from looking at the car, but I got back on it Monday night. After a few days of first trying to figure out why the fan was running all the time it soon quit running at all. Didn't matter if the AC was on, or if you let it idle for a few minutes. The fan just wouldn't come on. We ordered a new fan and the same issue persists. I have played musical relays with the 4 greenish relays in the fuse box under the hood and I have also checked the 30? amp fuse for the fan as well. Nothing has resolved the issue. Any thoughts before I have them take it in for a pro to look it over? Is there a fan switch located somewhere?
Hmmm. Do you hae a Multitester/continuity tester? I'd check the wiring from the connector at the fan to the relay terminals. In the meantime, what has your temp gauge been saying? If there is no signal from the temp sender on the end of the cyl. head, the fan will run constantly; if it's shorted somehow, the fan won't come on- it's the opposite of most other sender types.
