I have an '04 MCS with Parking Distance Control. I bought the car used when it was only a couple of years old, and have had no real problems (except the damned HK amp) in the 70,000 miles I have put on it since. Shortly after I got the car, the PDC no longer operated. Not a big deal to me, so I didn't do anything about it for a year, when I replaced the burned-out fuse (#41). It worked once, and that was all. I ignored it.

Last week, I took the car in for an oil change. On the way home, and a hot day, I stopped at the drive-thru for lunch, and the engine overheated. First time ever. I let it cool down, got some fresh coolant (much had spewed out of the expansion tank cap), and got home. A check of the archives here indicated that idle overheating was most commonly caused by low coolant. This might have been the case here. Before I had this problem, I rarely checked it. Although I have my oil changed every 5,000 miles or so, and the oil-change people usually check it.

I reconnected my ScanGauge II (disconnected since the last inspection), and began to obsessively monitor the water temp. Previously, the gauge rarely got higher than the 190's. On Sunday, I drove into Manhattan. In the stop-and-go traffic of the city, the temp went to 220F. I parked, had lunch, and drove home, steady in the 190's. No obvious evidence of a leak before or after that one event.

I went through the Low Speed Resistor sticky here, trying to understand what might have happened. Not many of the symptoms described there matched with my one overheating. The A/C has always worked fine when needed, and still does.

I did note that the PDC shares its circuit with the Power Steering Fan, and that it is somehow connected to the radiator fan. But I am no electrical engineer, and I really hate fiddling with automotive electronics. I have never experienced a problem with the power steering.

My question, then, is there a step-by-step diagnostic test for isolating what may be the problem? I am about to try low-speed fan, and although it's pretty cool today for August, the high-speed fan. I will idle the car with the A/C off, turn on the A/C to see if the fan turns on low, and let it run to see if it switches to high. I get from the sticky that it will turn to high speed at about 225F (which I thought was already too high).

I understand that I can unplug the PDC module. Hopefully, that will cure the fuse-blowing since the PSF and the radiator fan must have been working in those years that the fuse was blown. Right?

Do I have to get underneath the car to see if the PSF and the radiator fan are working? I don't see them from the top of the engine bay, but I didn't have a flashlight, either.

 

The blowing fuse on the pdc is most mostlikly the result of the ps fan being stuck...grit gets into it and the bearings...gets it stuck...when it is then activated by the computer, it blows out the fuse...your plan seems ok, but fixing a item must include fixing broken items found along the way...or troubleshooting may be impossible since thongs don't work right when tested.
the fans are avalable for the ps system for about $133-180. You can sometimes remove it, blow it out and lube it foe a short term fix or unplug it(not recommended).

 

PS
On unmodified pre 2005 cars, the cooling fan for the radiator is on that fuse that is blown...the relay anyway...later cars were split...blown fuse = no radiator fan, no ps fan, no pdc....so no airflow...car overheats...some movement, car is ok (similar amount of air to low speed fan).
Many mini's also have a lowspeed fan failure...but the highspeed kicks in just prior to overheating....so many folks ignore it...usually resulting in a hot running car, and subpart ac operation....then longterm the compressor can fail....and a engine running 40+ degrees hotter than the tolerances were machined for is a bad thing longterm for wear...
Just mythoughs..good luck.

 

The ps fan replacement is about a 15 minute job...
Faster, simpler than an oilchange...you do need ramps, or jack+stands....driving up on a tall curb may work too....

 

First test: There was no radiator fan operation up through 235F on my ScanGauge with or without A/C. I can't find the PS fan from the top of the engine and the car is too low for me to get under (neighbor borrowed my ramps).

So I have to get some fan operation, first. Fan spins freely (in one direction).

I haven't tested the underhood relays, car's too hot right now.

 

Blown fuse....
Cause...most likely stuck ps fan...very common on unmodified wiring harnesses on pre 2005 cars....

 

Save a The ps fan can ONLY be accessed from the bottom....it is about 4 inches...sits in the middle more or less....about a foot behind the oil pan....is on a bracket...
2 bolts...one electric plug....and it will pop right off, bracket and all....might be riveted or screwed to the bracket...dealers sell it with a new bracket...you can save a $ getting the fan seperate ...

 

Not sure about '04 but here's how I tested my '06...

When using Scangauge or the instrument panel in Test Mode 7, you can observe the fan operation according to the specs below.

Fan Speed 1: ON at 105*C/221*F, OFF at 101*C/214*F
Fan Speed 2: ON at 112*C/234*F, back to Speed 1 at 108*C/226*F

Each time Speed 1 kicks in, the coolant temp begins to drop. Only with long idling and/or ambient temperature in the 90s will Speed 2 come on.

To test fan operation independently: disconnect wiring harness, use a jump wire to connect brown wire to ground (-), connect small red/green (or red/blue) wire to positive. Repeat by connecting larger red/green (or red/blue) wire to positive. Each time the fan should come on, one at a faster speed than the other. Usually it's the Speed 1 that fails due to lousy relay design.

 

Thanks, ZippyNH, I am ordering a new PS fan today. And thank you, Cadenza, this was precisely the info I was looking for. Although I erred in saying the fan rotated freely - using a long screwdriver (it's hard to get my hands in there), I was barely able to budge the blades in either direction.