Anyone have an idea what may cause the CC to not work? I have had the switch unit on the steering column replaced a while back and that did not resolve the issue. Someone mentioned that it could be a brake/clutch relay... not sure where or how to check this.

Any ideas if this may be it and where to find it?

Have a 98 A4 2.8 5Speed.

 

I resoldered 3 capacitors in the module and it worked for the first time after owning my car for 6yrs. Search "cruise control module glove box compartment".

 

Will do! Thanks.

 

You guys are just guessing. It could be the vacuum pump, a leak in the vacuum system, the cruise module, the stalk switch, the brake switch, the clutch switch, the vacuum diaphram at the throttle. That system is (unnecessarily) complicated and you need to be methodical aobut how you diagnose it.

Read this, I've used it several times.

Cruise Control Diagnostic for Non-DBW A4 Ver.1 (Longer than Long) - AudiWorld Forums

 

Most common issues are the cruise control switch and the module... I had both. My first test was checking continuity at the switch, and I found out it wasn't making contact. Cleaned the switch, problem solved; or so I thought. Opened up the CC module and refreshed the solder on the 3 rectangular capacitors, and CC hasn't missed a beat since then! (been about 1.5 years)

If both of these fail to fix CC, then that guide becomes useful IMO.

 

That's true what you say. Hence, why it took me 6yrs to try one method, because I was just too overwhelmed of the possible problems. I stumbled upon one post that said "how audible is the cruise control module when engaged". Someone said u could hear a faint clicking just where the module is, which is the relay being energized. I didn't hear it so maybe it was just that. I removed the module, resoldered the 3 capacitors, even from my naked eye I thought this was not gonna do anything cuz they appeared to be OK. After all that, I installed the module, left it hanging without closing the glovebox, drove 40kmph+ and heard a "CLICK". Voila! Sometimes it works, sometimes the relay just won't engage. I stretched out the little spring on the relay cuz I felt that it kept pulling the contact back.