UrS4boy

The rear wiper on my 98 C4 A6q Avant daily driver just quit last week. When I pushed the wiper stalk ahead, all I got is the rear washer pump spraying fluid, no movement of the wiper arm. I let it go for a few days but with winter on its way, I thought I better figure it out and fix it. The other day was nice and sunny so I went out to the avant and gave it a go.

Here is the trouble-shooting I went through:

1. Checked No. 18 fuse on the driver's end-of-dash fuse panel. It's fine. *IF* it had blown, then my first guess would have been a cracked/broken wire at the hatch hinge and a dead short. That would have been easy to fix.

No. 18 is under the yellow 20 Amp No. 17 fuel pump fuse:



2. Removed the plastic plate the hides some of the left hatch hinge and the inner end of the rubber wiring boot.

3. Pulled both ends of the wiring boot out of the body and hatch.

4. Inspected for broken wires. None. A couple have been fixed before (soldered and wrapped).




I fixed two that were cracking but we not actually cracked. Paid special attention to the Blue/yellow, thick brown and red/yellow wires that are connected to the rear wiper motor.

5. Used my digitial multimeter set to 0-20V DC to check for switched power coming into Fuse 18. Yup. 11V (engine off). So power to the fuse, but was there power to the "239" rear wiper relay?

6. Pulled the "239" rear wiper relay from the lunch box under the hood.



7. Opened and inspected the 239 relay (PN 445955529A0. Looked fantastic. Points are fine. No visible bad PC joints.







8. Poked around the internet and consulted my Bentley (pg. X 1034) for details about the J30 "239" rear wiper/washer relay. I found a diagram and have used it as a base to add more info:



Okay, so the blue/yellow wire is hot with the ignition turned to "on".

9. With the relay out, I checked for switched 12V on relay plate female pin 8/15 and pin 4/31 (ground) Got 11V (engine off).



10. Found my old fuel pump voltage testing harness (long length of 14 gauge wire with a shielded male spade connector on one end and a shielded female spade connector on the other end) from 2004 and used it to check for continuity from the relay to the rear wiper motor connector:



I disconnected the plug above and with a wire from the "239" base plate pin(s), I connected my digital multimeter (set to 2000 Ohms) to that wire and to the the appropriate pin in the three pin wipe motor connector:

a) Blue/yellow wire at the rear wiper motor connector to pin 8/15 on the relay plate. Check. (Reference Bentley X1034)
b) Red/yellow at rear wiper motor connector to pin 2/53 on the relay plate. Check.
c)Brown (ground) wire on the rear wiper motor connector to pin 4/31 on the relay plate. Check.

11. Rigged up a "safe" rear wiper motor test "harness" with a thin female spade connector (outside wrapped in electrical tape) and a short piece of wire with 12 mm stripped off the end and a thin aligator clip. The female spade connector went on the center (ground) pin on the motor harness (not the one from the relay, the one attached to the rear wiper motor).

12. Attempted to stimulate the motor with my 12V battery charger:

a) First trial - red charger clamp to blue/yellow wire location on the wiper motor and the black charger clamp to the center ground connection. Nada. Not a peep.
b) Second trial - moved the aligator clip to the red/yellow location on the wiper motor harness attached the red charger clamp to it and then re-attaced the black charger clamp to the center ground connection. Got a peep. More like a constipated HMMMM. Voltage was getting there but the motor does not want to go. Not looking good.

13. At that point, I described the 12 points above on my home forum (quattroworld) and asked for suggestions:

a) One person said that they found the issue to be the rear washer pump. So I removed my rear sub-speaker (OE BOSE) and the rear washer bottle and disconnected the pump harness. Plugged the "239" relay back in and tried the rear wiper again. Nada.

b) Crispynoodle (also posts here) suggested that I really didn't know if the 239 was working (I had assumed that it was based on the the rear washer pump was working (until I disconnected it). That said, I grabbed the digitial multimeter, set it to 20V DC and, with the 239 still in place:

i) connected the (+) to the blue/yellow pin of the motor harness (in the photo above) and the (-) to the brown terminal. Read 0V. Then I turned the ignition to "ON". Voltage went to 11 V. Okay. But since the blue/yellow wire is a constant on as well as a 12V feed into the 239 relay, that didn't really prove anything.
ii) connected the (+) to the red/yellow pin of the motor harness (in the photo above) and the (-) to the brown terminal. Read 0V. Then I turned the ignition to "ON". Still 0V. Then (drum roll), I pushed the avant wiper stalk ahead. Bingo. The voltage starts to cycle from 0V to 11V then back to 0V and then 11V....until I pushed the wiper stalk ahead to toggle the relay off. Okay the relay is working as it should.

14. I have to sadly realize that the wiring to the rear wiper motor is fine and the 239 relay is fine. For some reason, the rear wiper motor is knackered. So off it came. Here are the parts involved:



15. Brdman and qshipq have suggested that I will have to open up the rear wiper transmission (drill off the rivet heads and tap and use bolts to reassemble). Brdman's photo is below. qshipq (Scott J) says

"The Audi grease becomes audi glue at about the 10year mark, which if left unattended can cause other problems. As a rule I don't go after the motor, just the transmission. Clean out the old "glue" as best you can and put in some good (lightweight) synthetic grease and use screws or re-rivet the trans cover back on. Make sure you at least check the O-ring protecting the trans from outside elements. I have seen many of these over the years with seized transmissions that do not pop the fuse."


Photo courtesy of Brdman.

Next project: Rehabbing the wiper motor. (In the meantime, I *almost* like the wiperless hatch look)