Check My Thinking: 2004 s60 Engine Cooling Fan Topic is solved

JudgeRat · Post by **JudgeRat** » 06 May 2019, 19:38

Okay community, I need you to check my thinking here:

2004 (P2) s60 2.4L w/150k+ -- I'm pretty sure I've correctly diagnosed that my Engine Cooling Fan / FCU (Fan Control Unit) are the issue, but I want to make sure before I go throwing parts at it. Symptoms are that when the car and the a/c are running, the fan will come on (at a very low speed) for only about 3 tenths of a second before it goes off again for about the same length of time. Then it will come back on for about 3 tenths and go off for about the same repeatedly. Eventually, the a/c clutch will stop kicking in (assuming because condenser not getting cooled enough) and the engine will begin to overheat if I'm not driving around on the highway or something. There are absolutely no fault codes being thrown. I disconnected the fan connector earlier today and took a voltage meter to the ECM(?) side of it and got consistent 12-15VDC between the black and red (ground and hot) wires and a steady 0.03VDC between the black and orchid (ground and data) wires.

Since the data signal is steady coming to the fan connector but the operation of the fan is not steady, my assumption is that there is a fault in the FCU that causes the data signal to not be correctly translated to "turn the fan on and keep it on for now". The fact that no codes are being thrown made it difficult to get this far until i happened to observe the strange pseudo-fan behavior.

Am I correct in my thinking and I need to just plink down the cash to replace the fan/FCU unit, or is it possible that there is something else that could be causing this condition?

Post by **DeadEric** » 06 May 2019, 21:06

Double check that the fans are doing the same thing under other circumstances first.

Drive until the car is warmed up fully then let it idel. The fans should cycle to cool the coolant.
If they do the same thing you're on the right track. Although, without looking up the wiring and logic I'm not 100% sure on FCU.

JudgeRat · Post by **JudgeRat** » 06 May 2019, 21:49

Yeah, I may not have made that perfectly clear; I did allow it to come up to normal operating temperature and observed the same behavior then as well as when it started to overheat slightly (before i quickly shut it off).

Post by **jimmy57** » 06 May 2019, 22:52

Have the fault codes been read out?

JudgeRat · Post by **JudgeRat** » 06 May 2019, 23:22

I would've thought that there would've been some to read, but as stated in the original post:

"There are absolutely no fault codes being thrown."

and

"The fact that no codes are being thrown made it difficult to get this far until i happened to observe the strange pseudo-fan behavior."

JudgeRat · Post by **JudgeRat** » 07 May 2019, 08:33

Here is a video showing what is going on -- up to operating temperature, a/c on full blast on coldest settings, fan comes on weakly and shuts off repeatedly.

Cooling Fan.mov: (23.75 MiB) Downloaded 330 times

Post by **abscate** » 07 May 2019, 08:44

These cars will swing between 85-105 C coolant temperature at the sensor in normal operation

Running on the road, it should be at the thermostat temp or 87-90C. Stopped in traffic it will go up to 105C , the fans will come on , and cool back to 87C

JudgeRat · Post by **JudgeRat** » 07 May 2019, 08:55

Yeah, I get all that...but shouldn't the fan be running full blast when the a/c is on? Even in stop-and-go traffic, the fan never comes on more than the video shows and she starts to overheat because of it. I'm just trying to rule out any other possible causes before i spend the money on replacing the fan/fcu assembly.

Post by **abscate** » 07 May 2019, 09:19

I’ll have to go back to my jimmy training on a COTS AC system but I think the fan behaviors is complex on such a system. The fa;used is to control the high pressure side of the AC to get optimism cooling IIRC,

JudgeRat · Post by **JudgeRat** » 07 May 2019, 11:58

Yep, it performs double duty by cooling both the engine coolant radiator and the a/c condenser, and it's supposed to have 4 settings: OFF, ON-LOW, ON-MEDIUM, ON-HIGH. There is nothing in the Volvo repair manual about: "quickly vacillating between 'whimpy-on' and off over and over again". Once the a/c condenser gets hot enough because the fan isn't cooling it properly, the (brand new) compressor shuts off and won't come back on (as is correct behavior) and the engine will start to overheat (unless i get on the highway or turn the heater on full blast until i can get on the highway). All this is what makes me believe 89% that the FCU is flaked out. I just got back from the local pick-n-pull looking for a used one ($45) that I could test my theory with, but unfortunately they didn't have any p2 bodies that had the correct unit still in them. I'm supposed to be going by a specialist tomorrow morning to have them run a couple of quick (free) checks. If someone can rule out that there is any other reasonably possible fault that would cause this condition, I would go ahead and order a new replacement unit right away, but money is tight and ~$350 for just the part isn't cheap at the moment.