Check Engine Light and Fans Running

[2000c43]

My RS6 showed a yellow check engine light a month or so ago and, at the same time, I noticed that the fan(s) would run for several minutes after I shut of the car, even if the car had barely been driven. I also smelled some strong exhaust odor and the smell of gasoline. I took the car to the dealer and they said they couldn't find anything wrong with the car and the check engine light had gone out. Now, a month or so later, the car is doing it again...yellow check engine light and fan(s) running for many minutes after shutting off the car. I do not have the exhaust or gas smell this time though. Has anyone ever experienced these set of symptoms before? I am going to take the car back to the dealer but wanted to have as much information as I can before I take it.

[4everRS]

You need to scan it and see what the CEL is. My random guess is cooling system error. My random solution is new thermostat.

No clue on the gas smell.

[2000c43]

Thank you for the quick reply. The dealer gave me no report on the cel when I took it in last time, only that there was nothing wrong with the car. Ill ask them for the detail from the car's last visit to the shop when I take it in.

[V8weight]

It sounds like a bad coolant temp sensor... Explains the fan run on as we'll as the fuel smell, as a faulty sensor will affect the fuel trims. If its not reading right, the ecu doesn't know when to switch from cold open loop to closed loop operation. Still, like Kyle said, a scan is needed to isolate the problem.

[lswing]

Ross-Tech vcds should be mandatory for every owner. Scan when the cel light shows and you should see your problem...

[Bigglezworth]

Just did this. if your car is not overheating, it's not a bad Tstat. If your fan runs for a while after running, or if the high speed fan is coming on when cold, it's a coolant sensor.

[2000c43]

Thanks for the feedback. My car has never overheated so, based upon what I read here, it sounds like the coolant sensor. If that fixes the cel, fans running for no apparent reason after shut off, and the exhaust / fuel smell, that would be great. Any idea how much the coolant sensor replacement should cost, assuming that is in fact what is wrong with my car? Thanks again.

[ben916]

I had mine replaced for cheap insurance, at the same time as the timing belt/water pump/t-stat.
IIRC, I had them replace it with the GREEN one versus the BLACK one @ less than $100 (I would have to check my records)

[Bigglezworth]

Any idea how much the coolant sensor replacement should cost.$$ depends on where you order from, what 'quality' or 'name brand' of part you desire, and finally, whether or not you are DIY or paying for someone to do. $20 DIY. $100 Stealership. It can be swapped in as little as 5 mins or take longer if you have a stubborn one that is seized to the side housing walls. The plastic pin that retains the sensor has broken for people many times, so it's a good idea to buck up the additional $2 to get a new retainer clip too.

http://www.autopartsway.ca/PartList.cfm?Audi/2003/RS6/Base/4.2L_V8/allB/Cooling/Sensors/Engine_Coolant_Temperature_Sensor/pagenum1/tabS

[2000c43]

Thanks...for those who have had this happen before, is there a specific code the computer gives for the failed coolant sensor or is it a generic code that will state "coolant system". I am not familiar with how specific or not specific the codes can be. I am taking the car to the dealership in this case since the car was already there for the same symptoms recently.

[kday]

There is a CEL for "Performance Malfunction in Cooling System".

Note that you CAN have a failing thermostat without overheating. If the thermostat sticks open you will have "underheating" -- it will take too long to warm up, and won't stay warm enough on the highway. This will lead to a fault code, and (counterintutively) the fans will run all of the time, because the ECU treats cooling system malfunctions in the too-cold direction the same way it does in the too-hot direction.

I had this issue last winter (http://www.rs6.com/showthread.php/23644-After-run-fan-seems-possessed (http://www.rs6.com/showthread.php/23644-After-run-fan-seems-possessed?highlight=)). Initially I replaced the coolant temperature sensor since it's easy and cheap. Eventually I had to replace the thermostat. Replacing the thermostat is basically the same work as the timing belt service, so they should be done at the same time.

[ttboost]

It can be swapped in as little as 5 mins or take longer if you have a stubborn one that is seized to the side housing walls. The plastic pin that retains the sensor has broken for people many times, so it's a good idea to buck up the additional $2 to get a new retainer clip too.

http://www.autopartsway.ca/PartList.cfm?Audi/2003/RS6/Base/4.2L_V8/allB/Cooling/Sensors/Engine_Coolant_Temperature_Sensor/pagenum1/tabS

...or worse than breaking the clip, is dropping it and not hearing it hit something...or hit the ground...which it never will.

I tied a small wire to mine so I always have it tethered...if I drop it...I pull it back up. You need small hands to get in there, but if all goes well...a 5 minute job...if something goes awry..all bets are off...

[2000c43]

Thank you again for the help. I had the coolant temperature sensor replaced and the check engine light is gone and the fans aren't running after the car is turned off anymore. All seems good now.