Guide: 4.2 TDI N488 Coolant Valve
 

As mentioned in previous threads, the D4 A8 has some issues with the transmission coolant valves - the N488 in particular. This part was recalled by Audi USA but not in Europe for unknown reasons.

People have posted info on the American forums but this isn't relevant to the 4.2 TDI as they don't have that engine over there, and the valve is in a completely different location.

Mine has recently given me a fault code so I've just done the replacement myself.

The latest part number for the N488 valve is 4H0121670A - mine was originally fitted with 4H0121670 (without the 'A' suffix).

Steps to replace below:

1. Remove main undertray.

2. The valve is located behind the passenger-side intercooler. There are 2 identical-looking valves back-to-back, one with a brown plug and one with a black plug. The N488 is the one with a brown plug. The black plug is the N509 (which apparently can cause similar issues). It's not easy to see the plugs from below, but the N488 faces the front of the car, and the N509 faces the back of the car.

3. The N488 is harder to access than the N509 as there is limited space between the valve and the intercooler. It is secured by 2x T30 bolts. Remove the 2 coolant pipes first (secured with spring clamps) to gain some space - some water will drain out here but not a huge amount.

4. I couldn't fit a 1/4" ratchet with a T30 bit into the space, so I had to use a T30 torx key to undo the 2 securing bolts. It took a while to fully unwind these bolts as access is tight.

5. The valve will drop down once the 2 bolts have been removed. Unplug the electrical connector and inspect the wiring for corrosion. These valves can leak coolant into the wiring harness when they fail.

6. Fit the replacement valve in reverse order (bolt it back on before replacing the coolant pipes).

I did all of this on the ground with the air suspension in lift-mode but it would probably be easier to jack the car up.

Hope this helps anybody looking for info on this job.