tjf

I just finished up a 1780 mile road trip. The car ran great for 1760 miles. About 20 miles from home I stopped to fill up the tank ad noticed the fan running. I thought it odd, as even though I had been running fairly hard, it was not all that hot - maybe 80. I got home and shut it off. - The fan kept running and running. I had the fan short, or open to ground, fault. I assume a drive is built into the back of the motor, and when it faults, it just goes to full speed. This is probably why it is so expensive.
BTW - Fuse #17 on the passenger side fuse box will kill the fans without disconnecting the battery (I did this 1st, to keep it from fully discharging). I found a vague comment about this fuse from one of Mishar's posts, but nothing that really stated pulling this fuse will stop the fans.
How common are these fan failures? Should I spend $550 dollars on a new one, or go used (~$80)? Replace one or both? It's a lot of work to replace. .....I just replaced the radiator in Jan.

Jack88

Often the failure is actually the temperature sensor. If I recall correctly, the sensor goes out and the car, lacking an input, assumes worst case and turns the fan on high, and keeps it on even after you shut it off.

TSHong

+1, Most cases here I think have been bad temp sensors.

MP4.2+6.0

+2. Yep, clear the cooling system fault codes, assuming some are there. If jet engine fan stuff stops, it is likely the temp sender (and the codes may say that). Sort of a pain to change, but by age of D3's now, almost expect it to fail. When not if.

Or, if issues kicks right back in after a code clear or you found codes saying fan issue, then yes the fan assembly. And yes, I think what used to be called the fan pack that controlled the fan speeds is all built into the fan now. Fans don't fail much, so at age of car you may opt for used if you can find one from a car not crunched in front.

tjf

The Codes come right back.
Where is the temp sensor located? Bentley just shows an x and no diagram and I can't see it.- I do know It's not in the lower radiator hose like on the 2.8. I actually have one I can install.
There are a few fans on ebay, both singles and whole front fan assembly.

MP4.2+6.0

Search on sensor location on this forum for more specifics. There have been posts on it. When you find the posts, you should also find info about being careful with the plastic retaining clip it uses, maybe buying a second one or tying some dental floss to it for likely slip and drops, etc. In general it is buried deep down in the back of the motor but above the tranny/diff case--behind the motor V if you will. For the V8, I last did it on a 2000 C5 4.2 where step one was basically clear the air box and intake tube/hose plumbing out of there to even begin to see that area.

tjf

I Replaced the temp sensor. The right fan still runs continually, but only with ignition on, which is different. I did not run the engine, only reconnected all connectors and cleared all codes. These 2 came back.
18080 - Coolant Fan Control 1
P1672 - 004 - Open or Short to Ground
18308 - Coolant Fan Control 2
P1900 - 004 - Open or Short to Ground
I guess it's fan replacement time.

Jack88

That's interesting. That there was a change in status says something, be darned if I know what. Before ordering up a fan, I recommend taking a careful look at the wiring, both for the fans and temperature sensor. Look for any signs of degraded insulation or dirty contacts on the plugs.

MP4.2+6.0

Fan running only when motor on makes sense to me. It is in a protective mode since the codes are telling it something is broken. Yes, check the wiring and such, and then after that it really does seem like fan replace time. BTDT on my C5 4.2. FWIW, when I went to diagnose it I found a piece of old rubber ducting Audi used around the hood latch had rotted and dropped into fan, physically jamming it. Made it pretty easy to decide my fan was fried. And likewise it was in protective mode with the jet engine fan stuff.

tjf

You may be right about protection mode. I put the intake back together and ran it with the fan fuse pulled to let it get up to normal temp. Put the fuse in and just the pass side fan runs. I'm thinking the drivers side has failed so the pass goes into protection. I pushed drivers fan blade a bit and it looks like it wants to run, but it doesn't take off. Turning off the engine, it pass side continues to run with the engine off, as long as it is warm. I found a used fan set on ebay and ordered.