Long time reader, first time posting. 2004 A4 1.8L quattro with 100,000 miles. Impeccably maintained now and also by previous owner. However, I have developed an oil leak. It seems to collect at or come from a semi round component with cooling fins on it. The right front axle goes into this differential looking unit. Any ideas as to what this unit is? Do they go bad? Are they filled with regular oil? Or could the origin of this leak be above this diff unit and is leaking onto it? Engine oil dip stick reads full. I have crawled under, over, around and through the undercarriage and engine compartment, or at least as much as a middle-aged fat guy can. Have also checked at rear of the engine and fire wall...can't detect any leaking oil. Any ideas or comments would be appreciated.

 

Does the oil have a tint to it? A color? Swipe your finger and look closely. If it's red it could be transmission oil and that does come from your differential.

 

Does it look like this?




If so, its most likely the tranny/axle seal...

 

If it's that it could also be the CV boot...

 

Thanks to all. There is no "color" to the fluid. It's not red like tranny fluid, it's definitely just the color of clean oil. I think then it must be coming from something above, or in front of the front diff and the oil is just dripping onto it...and then onto the garage floor. All the boots look good. No tears. The areas where the axle goes into the diff is nice and dry. The CE light came on last night and today I pulled codes P0171 & P0507. Any other ideas? I believe I might be planning a trip to the mechanic next week...a good Audi wrangler in Salt Lake City. Not cheap, but better than the dealer.

 

Dont know about your fluid, but my tranny fluid (Pentosin) is a clear amber - like clean oil. Wipe it up as best you can and goe for a drive. Check it when you get back check for oil.


P0171: System Too Lean Bank 1

P0507: Idle Air Control System RPM Higher Than Expected


Look for a vaccum leak or dirty Idle Air Motor (sticking open)

 

Ok, here is the scoop. Went to private Audi mechanic yesterday. #1. Crankcase vent valve, hoses & tubing all needed to be replaced...major vacume leak! #2. Valve cover gasket leak. #3. Plug change long over due. #4. Air filter replacement needed. #5. Good once over of the car, nothing else needed. Called me with differential diagnosis including estimated cost. Did not start work without permission. End result $590 later, everything fixed. Holy!%$#@!!! does this car run well! After getting estimate, called the dealer & asked how much the same work would cost. Depending on what the dealer found...$800+. So spent a few rubles less than the dealer. Very satisfied with the work. No oil on the front diff or garage floor. CEL off. Idle smooth. Happy Audi motoring to all. I love my A4.