[HELP?] Cooling fan still going nuts!

[Other_Erik]

After all the gentle nudges trying to get my cooling fans to stop going ballistic, I'm still in the same predicament...

P2181 (Malfunction in Engine Cooling System) - sometimes sets CEL, sometimes doesnt

^^ Whenever that code shows up, the cooling fans go absolutely bonkers. Outside temp, engine temp don't matter - Key to on position = full speed cooling fans sounding like a jet engine until 400 seconds after pulling key from ignition. So far the following has been addressed:

Thermostat, Water Pump, WP gasket - all performed with Timing Belt job
Coolant temperature sensor - even though the gauge on the dash was correct, replaced that along with its' little rubber o-ring and even a new plastic C-clip to hold it in place (I didn't even drop the clip! go me!)
Ambient Air Temp Sensor - Chalking this one up to damage from the pothole, I found it strung along the top of the front bumper support, and one wire had been cut clean through. Reattached with soldered joints, re-wrapped, and outside temp displays correctly now (no more -22F when it's 30F in the morning)

Only a few things I can think of that could still be wrong here

1) Engine cooling fan switch: 8D0959481B (don't know where this goes, but can probably find in the Bentley manual) - correct my part number if it's wrong, going by results from the Google machine, so not guaranteeing that's the right part!
2) Cooling Fan Relay (part number unknown) Will again have to look this one up in the Bentley, hopefully they've got a part number for me
3) Bad cooling fan/fan clutch
4) ?????

I've checked the fans by hand (obviously long after they stopped spinning on their own), they spin freely, and the clutches are not terribly warm for being in the engine bay of the beast.

Any further thoughts on diagnostics for me? I absolutely hate it that when I'm sitting at a dead stop, all I can hear is these damn fans and my voltage gauge shows juuuuuust under the 12v mark, sometimes as low as 10v.

Oh, clearing DTC's with the Vag-Com causes the fans to stop going nuts... for a while. Sometimes a few minutes, sometimes a few days of back and forth commute, but they KEEP... COMING... BACK! It wouldn't be so bad, but one thing will sometimes fix it for awhile, but I'm not getting consistent results no matter what I do.

Thanks!
O_E

[lswing]

I always worry about soldered wires. Any chance the solder would affect the current flow or something odd like that? Maybe another wire shorting out as this seems to be intermittent.

Ambient Air Temp Sensor - Chalking this one up to damage from the pothole, I found it strung along the top of the front bumper support, and one wire had been cut clean through. Reattached with soldered joints, re-wrapped, and outside temp displays correctly now (no more -22F when it's 30F in the morning)

[Other_Erik]

I always worry about soldered wires. Any chance the solder would affect the current flow or something odd like that? Maybe another wire shorting out as this seems to be intermittent.

Ambient Air Temp Sensor - Chalking this one up to damage from the pothole, I found it strung along the top of the front bumper support, and one wire had been cut clean through. Reattached with soldered joints, re-wrapped, and outside temp displays correctly now (no more -22F when it's 30F in the morning)

I wouldn't worry about it here. Solder is _not_ the way to go for high current / high draw applications since it can induce the current, but in a sensor wire the difference would be nominal - might show 1 degree F difference in this case. Before hitting this wire, I was getting a different code (don't have the log in front of me at the moment) that said Ambient Air Temp Sensor intermittent no signal / short to ground. No codes regarding Ambient Temp Sensor since the solder job.

O_E

[SteveKen]

HVAC head unit or wiring to/from it to the ECU.

I've also had the fans stay on forever a few times after flashing new ECU code (normally wrong ECU code).

[Other_Erik]

Dual thermal switch per Jim Ellis Audi (I know, don't trust their part numbers/diagrams):
8D0959481B, 8D0121049H

Am I just getting myself more confused?

O_E

[kruat]

I'm sure you know this, but the fans going nuts are due to the cell thrown. Coolant temp switches, thermostats, ambient temp sensors, even an AC system can cause the fans to go nuts. Check all connections for the fans. V8 S4s have a secondary check valve coming off the drivers side rad, and if that fails it throws a cooling system performance fault, do our 4.2tts have the same valve?

[mrdave]

Does the vag-com reading give you any more information than just the P2181 code?

Also, good information here: http://www.rs6.com/showthread.php/23644-After-run-fan-seems-possessed

[Other_Erik]

Does the vag-com reading give you any more information than just the P2181 code?

Also, good information here: http://www.rs6.com/showthread.php/23644-After-run-fan-seems-possessed

I'm second-to-last post in there, also took the step of swapping in a new coolant temp sensor and burping out the air that made its way in during that step.
Vag-Com only gives me the one code P2181, which is really an oddly vague code for a car with so many sensors. You'd think they'd have individual codes per sensor, relay, etc...


I'm sure you know this, but the fans going nuts are due to the cell thrown. Coolant temp switches, thermostats, ambient temp sensors, even an AC system can cause the fans to go nuts. Check all connections for the fans. V8 S4s have a secondary check valve coming off the drivers side rad, and if that fails it throws a cooling system performance fault, do our 4.2tts have the same valve?

Checked every connection I could find, every plug is tight and locked in. Hoping it's not a check valve because that means bumper off to get to the part, check it, get the part number and order if it has failed, then bumper back on, wait until the next weekend, bumper off again, etc...


-----------------------------------

All of this is very annoying when the car is working flawlessly minus the fans deciding to kick on for no reason.

I think I may just end up ordering a J271 relay to see if that solves it. Hate throwing parts at a problem, but the code is too vague to do any in-depth troubleshooting.

O_E

[Other_Erik]

P2181 Malfunction in Engine Cooling System
008 - Implausible Signal -- Intermittent -- MIL On

That's beyond frustrating.

[RSoverAll]

Fawk, still no resolution?

Bentley mostly references the water pump, t-stat, and coolant temp sensor for P2181.

I have installed a bad one right out of the box before, although it was the cheapest one I could find- MTC.

Have you checked the harness for integrity from the sensor to the ECU? Checked the sensor for continuity?

Graphed the reported values with VCDS?

If it's intermittent that makes me think it's in the harness... Usually a bad sensor is bad all the time.

[Other_Erik]

Fawk, still no resolution?

Bentley mostly references the water pump, t-stat, and coolant temp sensor for P2181.

I have installed a bad one right out of the box before, although it was the cheapest one I could find- MTC.

Have you checked the harness for integrity from the sensor to the ECU? Checked the sensor for continuity?

Graphed the reported values with VCDS?

If it's intermittent that makes me think it's in the harness... Usually a bad sensor is bad all the time.

Still no love. Coolant Temp Sensor was original, replaced with OE Green, and what a bitch-bastard it was to get the old one out - brittle plastic wedged into the port did not want to do anything but snap apart and leave me with just enough of the edge to get a pair of spudgers jammed underneath and pry it out. New one went in without issue and I managed to get the C-clip on without dropping it. From troubleshooting, I don't think it's the t-stat or the water pump, both were replaced with the timing belt July of last year, OE gear, and I'm not having any funny engine temperature issues - it warms up fine, t-stat opens when the temp is almost at the half mark and dips back down for a bit, then back up to half mark, and stays right there. I'll be pulling up ye olde Vag-Com to start logging data to see if I can find any sensor giving crap signals, but not sure which blocks I should log.

Everything seems to have started going to crap after the pothole incident last June, and it's not leaving me with a warm fuzzy feeling...

O_E

[nene]

Other_E,
I found the following notes on the RossTech site. It appears you already have their tool, thus I recommend following some of the notes on the list below.
If you have a voltage meter, you may be able to check the harness points to see if there is any drop in voltage from source to target.

Possible Solutions
Check G62 - Engine Coolant Temperature Sender
Inspect wiring for G62 (Coolant Migration, damage, corrosion, etc)

Check (if applicable) G83 - Radiator Outlet, Coolant Temperature Sender
Inspect wiring for G83 (Coolant Migration, damage, corrosion, etc)

Check Coolant Thermostat
Use Graph function in VCDS, Measuring Value Blocks - MVB
Start Engine cold, graph Coolant Temperature Sender (G62) Typically MVB Group-001
Hold RPM around 1,500rpm and watch coolant temp increase in Graph until thermostat opens, indicated by a slight drop in coolant temp
If coolant temp drops below minimum operating temperature (80°C) or never reaches operating temperature, (verified by external thermometer) suspect failed thermostat

Vehicles with both G62-Engine Outlet, Coolant Temperature Sensor and G83-Radiator Outlet, Coolant Temperature Sensor
Use Measuring Value Block group MVB-130 instead on MVB-001
G62 should increase in Temperature before G83 increase when engine coolant is cold
G83 will increase when the thermostat opens and after G62 reaches operating temperature (80°C)
If G62 and G83 both increase while engine warms up, suspect failed thermostat


Ross Tech Notes on P2181 (http://wiki.ross-tech.com/wiki/index.php/18613/P2181/008577)


For my 70K mile service the tech also replaced any wires he found that appeared to have cracks. Most appear to be ok, but some vacuum lines had to be replaced. Would not affect the fan going off for sure. I've had the fan go crazy occasionally and once I cleared the codes the fan would stop messing up for weeks. I am hoping it is all resolved with this big service which also included change of some of the items noted in the above list.
Good luck and keep us posted.

[Other_Erik]

Thanks Nene, I'll look into these either late this afternoon or tomorrow. If it turns out to be t-stat stuck open (I don't think so, but we'll see), or water pump failure, at least the place I had the work done has a 2-year P&L warranty and it'll be on them to sort it.

Knowing my luck, though, I'll have a sporadic signal drop from one or both sensors and have to multi-meter it from one end to the other to figure it out.

Thanks
O_E

[Other_Erik]

So after weeks and weeks and weeks of problems, it's finally resolved!

Betcha want to know how I resolved it, don't you?

Well, I'd like to know as well. I've been logging every drive, looking up every thrown code, checking every connection, and can't find a damn thing wrong with it since the last code thrown 4/10...

Last fix was resoldering the ambient temp sensor wire and replacing the tstat on 3/17.
Codes continued to be thrown through the 10th of April
NO CHANGES were made other than to continue clearing the P2181 code
Since 4/10 (300 miles of driving, multiple short distance {<15 miles} and some medium distance {15-30 mile} trips), no P2181 code.

I guess I scared the gremlins away with my determined attitude and persistence in checking _every_ _single_ _connection_...

Now watch, I'll have jinxed myself and the radiator will spontaneously detonate on the way home today :\

O_E

[RSoverAll]

Well for your sanity's sake, I hope it stays fixed this time.

[Other_Erik]

Well for your sanity's sake, I hope it stays fixed this time.

Thanks, I hope so too...

As an aside, when you pulled your onstar module and battery, was there a piece of sheet metal bolted on top of it to hold it in place on the footwell side of the firewall? I pulled my carpet up, but thanks to my f***ed up back, I can't bend myself at the proper angle to get in there and pull the upper bolt holding the sheet metal in place. Before I ask my wife to get in there and fiddle with things, I want to make sure I'm asking her to yank the right part out...

O_E

[ben916]

PM replied