wug

Thanks guys for all this info. I am going to replace this sensor next week in a way that MP4.2+6.0 described. This is a crazy job for a bloody sensor. At this point i hate Audi engineers or whoever designed the engine. Btw. Audi dealer quoted me for 2000 euro and 2 days job.

MP4.2+6.0

others have pointed out the whole W12 intake manifold is quite light in spite of its size because of its magnesium casting. Also confirmed in some other posts from folks who have done it that it is not particularly difficult to pull, and actually perhaps an easier way to do the spark plugs and also avoid the absurdly expensive gaskets used if you separate the manifold runners and decide to change those gaskets.

wug

Thanks for reply! This is the way i will try first and see how it goes. Also i will find out about those expensive gaskets you mentioned like price wise. Yesterday i got the red light warning again. Cleared with VCDS and then drove about 150 km without any problems.

MP4.2+6.0

Just so we are on the same page, there are two approaches involving the intake when it comes to spark plugs, and in turn what you can do, the punch line being #2 is the obvious one:

1. Separate each half of the runners at the respective seams. Again, while several replies came back that folks are re using those gaskets, if you replaced them list is >$150 EACH--you need two. This is how Bentley documents it, and how my dealer did the plugs at the first 35K mile interval.

2. Pull the entire intake up from the top of the "riser" at the center--those bolts are under that center black trim cover at the centerline of the intake. Then there is only one gasket below, which again some replies coming back also saying it was re used, but the price of that gasket is a much more rational few tens of dollars anyway. On my last plug service at the dealer when car was still under service plan, that is what they did from looking at the parts list on the invoice.

#2 of course gets more out of the way anyway for getting at the back of the motor, since #1 leaves behind a lot of the center area of the upper manifolds.

wug

For the last 6 months i haven't had any red lights at all. I know that sounds crazy but i refused to replace the G62 due to the engine removal job and i guess it was a good move. There was no more engine coolant temperature errors. Obviously to do that i had the laptop with VAG-COM always in my trunk just in case light goes red again. So, again Audi surprises me with this weird symptoms ...

03_AR_CO

#2 is absolutely the way to go, $9.00 intake mainfold gasket was reason number 1. I did this procedure this weekend, and it is very easy to do. I did a major tune-up new air filters, plugs, coil packs, and had an O2 sensor to replace as well. I took my time on Saturday and had everything apart and back together in about 4 hours. Could have done it in less time, but I was being very careful being this was my first encounter with the W12. Also I can confirm that the intake manifold is extremely light weight.

tlc215

Hi,

I have the same car and exact same issue. Was it just the sensor? My mechanic wants to change out water pump as well.

Thanks!

MP4.2+6.0

There are other threads on the W12 subject that are more current than this one--last posted in 5 years ago...

Your issue should be either the coolant temp sensor or the thermostat, and is more likely the sensor from (only) the info provided. It is not the water pump--from any W12 experience I can recall on this board for literally ten + years. The sensor and the thermostat can be a bit tricky to isolate one vs. the other on a W12. No reading at all ever on gauge would suggest it is the sender, but a basic diagnostic step may have been missed--more below. Expect to replace both by 100-150K miles.

Coolant temp sensor is probably the more likely if never changed before; many of us have had to do it on W12's. The step that may have been missed though is to clear all codes in the engine computer ECU. W12's have TWO, so both ECU 1 and 2 must be cleared. Look for a coolant related code in there. If you/mechanic are using a OBDII generic (aka CRAP) code reader, you probably are losing the diagnostic codes for more esoteric areas like this, plus you won't even be able to access or clear ECU 2--or any other module in the car. The reason the fans are at full blast and coolant sensor reads nothing is it is locked in a protective mode thinking there may be a real cooling issue. After you clear codes with a decent tool (eg VCDS/VAG COM), the fans should turn off and the gauge may come to life. If it does and stays working, it may not be sensor. Then use std. diagnostic techniques for thermostat--does it overheat, is it slow to warm up even if it never overheats, etc? If thermostat seems okay and gauge now reading, it is probably the sensor. Drive it and it will probably choke again--maybe a few weeks, maybe less. Watch for gauge just falling off cliff to zero. That is when protective mode is kicking in, going back again to either sensor or thermostat.

BTW, this thread is also out of date on the procedure we owners came to and shared for the sensor change out. You do it by taking off the upper half of the intake manifold, which is same better technique for spark plug changes. Search for threads on it. In particular, you do NOT have to pull the engine, which is what some dealers did early on and Bentley manual (wrongly) says you have to do.

tlc215

Thanks for the response! I told them to hold off on the work for now. I should have told you the first thing they replaced was the expansion tank to solve this issue. That didn't solve the problem. So after they did a reset ..I picked up the car and the error was gone. I put on about 500 miles before the coolant alarm came on ,again, and the gauge dropped to cold....again. Not sure if this new info helps, but any info is helpful. I appreciate it!!!

MP4.2+6.0

Gauge that works after a clearing of codes but then drops to zero after driving suggests to me it may be thermostat. Is car slow to warm? Or, do you ever drive it in very cold temperatures (like 0F/-18C) where heaterr may hardly even work). Any sign of it overheating when air temps are warmer. What is the specific code it is reporting?