Tony1997A4

This is how I fixed my cruise control in a 1997 A4 Quattro: So my cruise control started to quit on me while driving down the highway. It kept cutting out after about 5 minutes and then it would not work until I waited an hour or so (with it off), but then it would only work for a couple of minutes and quit again.

I found out that the cruise control is deactivated from any of a number of sources including a drop in vacuum from the pump or either of the clutch or brake vacuum release switches, the brake light switch, the backup cruise control brake light or clutch switches, the cruise control ECU unit, or the cruise control switch itself (on the signal light arm). Yikes!
I first checked that my vacuum lines and pump were holding pressure. Then I pulled the CC switch apart most on the signal light arm and carefully scraped the tarnish off of the electrical connector (I couldn't get it all apart without breaking it though) - this helped the cruise to stay on for about 10 minutes before quitting on the highway. Now I'm thinking its a resistance issue (between this switch and the ECU) so I pay to have the arm and switched replaced at the dealer - $395 Canadian. Then the CC worked for about 20 minutes before quitting. Still thinking resistance I disconnected the clutch and brake CC/vacuum electrical connections and the CC worked for about 30 minutes before quitting - crap, now I know that the ECU is next and while it takes 3 minutes to install behind the glove compartment the unit is $450 Canadian - but I lucked out and found a used one out of a 1998 VW Passat for $140, put it in and the CC works perfectly.
I still think there is resistance in the clutch and brake switches though so I left them dissconnected - the brake light, brake vacuum and clutch vacuum switches still disengage the CC, so I don't notice any difference when driving. I have a feeling the resistance built up everywhere and caused the ECU to fry a diode, which would then cause other components in the ECU to heat up and eventually shut down the CC ECU.

Timbo717200

Thanks for your info, I had the same problem until 49000 miles. Told the Audi dealership that I wanted the sending unit from the transmission to be replaced, said I would like to speak to the area service rep about the lack of dependable cruise contol for 49000 miles. They replaced the sending unit and no more problems.