MP4.2+6.0

I am documenting the D3 A8 W12 cooling temperature sensor replacement. Pictures at end. Known as the G62 sensor. A commodity part--simple two wire sensor held in by a plastic clip. The big trouble is, it is buried behind the motor and very hard to get to. The Bentley manual for the W12 sensor job starts basically with the classic infamous step 1 for high powered cars with big engines stuffed in: "pull motor." Hence the practical learning here.

A few people actually had to pay for that motor pull. But, in the last couple of years as we have exchanged posts on spark plug and other jobs involving the intake manifold, it became evident it may be practical to do it with motor in place; barely, but do-able. If vehicle needs a spark plug change anyway, a good job to pair up with that thorough tune up cycle.

Here is a post from early 2014 for example where it worked: W12 Rotors/Pads, Plugs/Coils, Coolant Tubes/Hose, G62 Temp Sensor, OH WHAT A DAY !!!! - Page 2 - AudiWorld Forums I thought I would post more of a general "how to" here, given I just did it this afternoon, first person.

Stats/symtoms: 109K miles. No cooling or heating issues in any recent timeframe. Out of blue on trip back from Sierras on a cold (sub freezing) winter night with lots of coasting down long grades, temp. gauge suddenly descended rapidly to zero and red center instrument warning display came on about checking coolant. Heater was blowing nice warm air reliably so I pretty much knew coolant was present, flowing and at operating temp. Years ago on my 1985 Audi 5000 I had the same diving gauge stuff with the previously oft unreliable old Audi 4 prong temp sensor. Stopped and checked at a gas station to be sure--coolant all fine, but fans kicked to high even with all A/C off. Fans continued running post shut down too, which is rare for me at all and unheard of in winter. Later in drive--after a food stop--it read fine and did for next few weeks. The other night--also cold--it returned, this time with no reading on temp gauge and a CEL and code that tied to temp./cooling system. Again, after that one drive it returned to normal. But, having seen it twice I figured I would tackle the job. I've been on a "zero problems" kick for a while so this one had to go away for good.

Basic parts:

• G62 sender 06A-919-501A, approx $26 discounted dealer.
• O ring N903-168-02, $1+. I eventually lost this in the never-never land behind the motor so I ended up re using the prior one (still pliable and no deterioration). Should have ordered two. BUT, working clearances are so tight it would likely have been impossible to get circlip back on anyway with a new o ring, even with the plumbers grease I lightly used on it (and when it fell off).
• Plastic retaining clip 032-121-142. $1+ I ordered two of these, but did it finally with just the first one. The one I pulled was somewhat deformed, so good to replace especially with o ring re-use.
• Gasket for the base of the intake manifold riser area (also used for spark plug job): 07C-133-238H. $10.

Job major steps are (none documented in Bentley since they say pull motor):

1. Pull intake at the center where the T30 Torx screws are, removing the large rubber intake hoses from both air boxes, detaching the various vacuum, oil vapor and similar hoses, and undoing the electronic throttle connectors. There is one final vapor/air hose underneath toward the back of the (U.S.) passenger side you need to undo after tilting manifold up. Either that, or you need to take off the passenger side throttle body, which involves another gasket that is moderately expensive if replaced. You can see the hose toward the back of the (U.S.) passenger side of the manifold in the first picture below--still attached, and why I had tilted it up like that. It may look big, but it is a nice magnesium casting and all in weighs 10lbs or less. Having done my C5 4.2 a few times as well as the old C4 2.8, this manifold is actually a pretty easy pull and replace.
2. Tape off manifold intake. Later on, various bits of plastic or other stuff may fly around from misc. old cracking trim type stuff. Also, be very careful with the oil vapor hoses. Between last pull and this one two of the four plastic vapor hoses have cracked even with a lot of care. By 100K+ miles they are pretty cooked and rigid. Same thing on my prior two A6's (2.8 and 4.2). Fairly pricy parts and hard to repair well.
3. Get everything out of the way you can toward the back of the driver's side head and valve cover--various hoses, connectors, etc.
4. Maybe optional, but helpful: I pulled the whole wiring harness to the plug coils and the injectors on the driver's side cylinder head. Doing so allowed me to get my hand in better toward the back of the valve cover, since that wiring harness uses the same crucial passage space. If you do this label each coil and injector connector with the cylinder number; dealer had done so back when they did the valve cover gasket, and I re did it with a silver Sharpie.
5. Maybe optional but also helpful: Pull cam sensor for intake cam off back of cylinder head on driver's side. That cam sensor is basically right in line with where your hand needs to go to get down to temp sender, It is painful to unscrew with a 5mm allen wrench 1/6 or ⅓ of a turn at a time, but can be done if you are able to work with tools by feel only and keep a decent grip on them and loosened screw. As I confirmed with the o ring, if it falls in there, low chance of recovering. Even with belly pan off and blowing air, I never found the o ring for example.
6. Undo rest of connectors to sensors at back of head area to get better working room in there. I changed an exhaust cam positioning sensor on the same head last year and broke the connector locking tang. I did that without a manifold pull BTW, but it was a tough fit and same more blind allen wrench turning. This time with all the connectors undone I got a new factory connector end back on it that I had ordered from the dealer before; FWIW even without locking tag connector was still firmly on. When they cook with age I can pretty much shatter the plastic connectors with careful pliers work and get to the small metal terminals unscathed and ready to push into a new connector body. Took about 10 extra minutes once I had connector ends free.
7. Pull connector off coolant sensor. All the connectors in this area are the typical ones for the motor stuff where you have to push in a bit while pressing the locking tab downward and then pulling it off.
8. Remove retaining plastic circlip off sensor where it pushes into the metal water line. I got in there with a very small screwdriver (5 inches long or so with pretty fine/small blade; smallest Craftsman in the sets). That gave me the slight leverage I needed.
9. Before pulling cooling sensor, make sure water lines are blocked. I pulled only one in back of manifold area, but guess what... Old sensor made a good plug for the line as it turned out, and I put a rubber plug on the "male" metal pipe end. You can see an open fuel line if you look carefully toward the back center in the second picture, and next to it is the offending cooling line outlet. Visible closer up in the fourth picture.
10. Pull cooling temp. sensor upward and out. Shouldn't need too much force or pliers or anything. Just a press fit once the retaining plastic circlip is out.
11. Make sure the sensor o ring is out if you are replacing it. My sense is not to use a new one, even though I had planned to do so before losing it. I could get one at local dealer in the morning but decided it would be really hard to get the sensor in and get enough pressure on it to engage the clip. I tried, including direct screwdriver vertical force before I lost the o ring. The old circlip was deformed, a sign it took a good amount of pressure initially even with hose/motor out of car when it was built at factory. I applied some plumbers high temp grease (grease, not putty) in a very thin coat.
12. Reinstall circlip. The single hardest part. You don't want to drop it. I ended up putting it in the opposite way from how I pulled the old one out. It doesn't matter.
13. If you pulled the cam sensor, reinstall. Use locktite there and on any bolts/screws in valve cover area. I found screws had backed out from the spark plug plastic wiring channel stuff that I had just put back 6K miles ago but without Locktite. Reattach all disconnected sensor connectors, and really double check.
14. Check all wire routing and clips back there. Your chance to clean it up, especially if you did things like O2 sensor replacements where clipping the wires factory style with the manifold in place is tough.
15. Replace all parts you pulled along the way involving the intake manifold. Remember that one "gotcha" hose under the intake you have to attach first to avoid pulling the passenger side throttle body.
16. Top up for lost coolant and bleed as needed.

I included some pictures below to give people a sense of:

• what the W12 intake manifold looks like coming off,
• the general work area,
• the rear of the cylinder head/clearance problem,
• how my arm just barely fits in there (I can see by looking to right with a good cordless light with good intensity), and
• where the sensor is down there.

On the last sensor shot, it is right in the center of the picture with the grayish sort of top where the electric connector fits on. It is almost impossible to see until most everything I stripped off is dispensed with, and even then only in a narrow viewing angle. The depth of field is also misleading. It is about 6" from the valve cover down to the sensor; hence why even with the intake off and some other disassembly it is a challenging job. But do-able with decent experience and ability to work in tight spaces, sometimes quasi blind. $50 or less in parts narrowly, instead of a "pull engine" nightmare if done "by the book." A few hundred is a reasonable budget if you also run into some aged plastic parts/hoses that break. If some oil vapor hoses break for example, you can probably tape/mend them temporarily, order them up, and install later even with manifold back in place with minimal disassembly.

2-3 hours for me; up to twice that if you know auto mechanics but have never been into the whole W12 intake and rear of motor area before. A fairly advanced skill job, but almost entirely to do with patience working in tight clearance areas with some tedious and quasi blind tool work. My XL glove sized hand are good for reach but harder to squeeze in too.

Mister Bally

Please tell me you don't have to remove the intake manifold to access that A/C fitting. Then again, you couldn't run the engine while connected to it and the manifold off.

Great write-up.

MP4.2+6.0

Didn't do anything with the A/C, and in general the HVAC stuff is not encumbered by the intake. Heater bleeds are easy and back w/ plenum stuff with the cover. Intake pull is typical to get to stuff involving the heads and valve covers. Bentley says pull side "wings" off it for things like spark plugs, but those involve absurd $150 gaskets. This pull is as fast or faster, uses a single $10 gasket, and as you can see from second picture opens everything up like a proverbial kitchen table. The W12 serious posters seem to have settled on this manifold pull. The intake pull and removing the air boxes at times are the typical go to ways to open up working space. There is yet more below for the intake, but that get into more disconnecting.

Thanks for kind words on write up. One of those last frontiers of W12 specialized work I figured I might end up doing some day. I still recall you diving deep in the back of the 4.2 to find yours, like my prior C5 4.2.

Mister Bally

I now see the clamp on the hose to pipe next to what I thought was an A/C connection. I don't think a squeeze clamp would hold on an A/C discharge line. Suction either.

MP4.2+6.0

Here's a picture of the pulled old sensor for posterity. I noticed it kind of looks like it may have not stayed 100% sealed at the crimp joint from the slight corrosion I saw at the base. It's in a super dry and hot area behind driver's side head up against firewall, so nothing else nearby would easily explain the deposits there.

Besides the all business look of the motor in general, as someone who has opened and torn down a bunch of motors, gotta love the look right down into the valves. 4V port injected on a D3 W12. 109.5K miles. Just std. oil changes with no oil added in between, Tier 1 gas and Techron once in a while. As clean as it gets--no touch up or cleaning for the pic. They all look like this or better. Doubt heads could come out in vehicle (I pulled a C5 4.2 head), so glad all looks top drawer and I got dealer to change valve cover gaskets at end of CPO.

heathrow99

I have just replaced both temp sensors on my bentley continental gt 2005. It took me 1 hour and a relaxed job at that. There is zero need to take off the manifolds etc. I purchased the two sensors from euro car parts for £16 each, all I did was quote vw part number 06A919501A. Do not buy from dealer.

OK, the front sensor is at front right of the car, looking at it direct on. it is more or less just behind the n/s front light, on the underneath of the main rad pipe coming out of radiator. I removed the front cover plate with the 12 screws just for ease of access, popped the main radiator pipe clip and pulled it back to gain access to sensor. Then simple remove and fit new one.

The rear is tight at the back of the engine, but it is at the top. removed a small vacuum pipe above it for ease of access. Then popped the clip securing old temp sensor and removed it. Fitted new sensor, The clip that holds it in is the pain, but after a few attempts, I got it in. Lost one clip, so get a extra spare one just in case.

Do not forget to clear codes

I could have done this job in half hour, nothing major to remove.

Giovanni Giovino 6.0+6.0TT

Hello Heathrow,
You are mixing apples and oranges here, the Bentley VS. the Audi W12 have different intake manifolds, the Audi W12 intake is much larger and shaped differently, so on the Audi you must 100% remove said intake to access the temp sensor at the rear of engine.