VCDS Cruise Control Diagnostic Issue

[Trevman]

Hey guys, So My cruise control doesn't work and I'm trying to figure out why. I have the full registered version of the latest VCDS software and a Ross-Tech KII USB interface.

I came across this great write up of how to figure out what the issue is http://www.wak-tt.com/vagcom/vagcomccbrakeclutch.htm

Except that my VCDS just displays "N/A" in the 4 fields when I'm in group 066. Other groups will display values in all 4 fields, but not 066.
Anybody know why?

[down_n_dapper]

There are many many reasons why cruise doesn't work, faulty stalk switch, faulty cruise module, any number of vacuum issues, but this topic has been covered before. Not sure you can diagnose with vcds as the system is fairly old and lacks a few sensors of newer cars.

I would search A4 B5 cruise control repair or something similar and go through the documented testing methods to test each component instead.

[MetalMan]

I think many AEB cars will require reheating/adding solder on the capacitors on the cruise control module. At least, that's what finally did it for me and many others.

Also these are the other main ones:
1) I think ABS must be operational (could be wrong)
2) The vacuum-operated cruise control system in the AEB has multiple items that must all be functional. You can trace them by starting at the actuator rod connected to the throttle body arm.
3) Cruise control stalk switch buttons need to be in good shape. There's a DIY out there which basically shows cleaning off the contacts of any surface oxidation/corrosion (usually using a pencil eraser).

[Trevman]

I've tested the ABS with VCDS and it's fine. no faults
I've also physically tested the vacuum components and those are good.
I recently installed a brand new stalk.

I tried resoldering the module, still doesn't work. (I followed a DIY for it, but there's a slim chance I just did it wrong)

So I think I'm down to the clutch switch, brake switch, or just a bad CC module.

[Trevman]

Emailed back and forth with Ross-Tech a bit. Here's the email they sent...

The AEB 1.8T used a non diagnostic capable CCS module per the "DBC (Drive-By-Cable)" notes here:

http://wiki.ross-tech.com/wiki/index...asuring_Values

The missing measuring data is normal because the engine controller doesn't directly control CCS. If the factory level repair manual you are using doesn't include manual diagnostic steps (vacuum pump motor, check valves, vent valve and similar) please feel free to join and post in our forum:

http://forums.ross-tech.com/forum.php

I don't know if all B5's are DBC, but apparently for the ones that are, the cruise control system can't be diagnosed through VAG-COM.

[MetalMan]

I don't know if all B5's are DBC, but apparently for the ones that are, the cruise control system can't be diagnosed through VAG-COM.

Only AEB engines are DBC (1996-1999.5).

Sorry to hear that it seems most common things seem like they should be working, but CC still isn't.

[walky_talky20]

If you tried the easy things, then you'll have to go further down the rabbit hole if you really want cruise. Personally, I find that cruise is not optional. I do 80 highway miles a day on my work commute and it simply has to work.

If you think the module is good, then you test it's inputs:
- make sure POWER and GROUND are good
- make sure CRUISE ON signal (from stalk) is good
- make sure CRUISE SET signal (from stalk) is good
- make sure BRAKE PEDAL UP and CLUTCH PEDAL UP signals are good.
- Make sure VEHICLE SPEED signal is good.

Everything could be 100% perfect, except the SET button contacts are dirty inside the stalk and it will never ever know you hit SET button. There is no way for the cruise module to tell you what is wrong. You just have to test all its inputs to see what is missing. If nothing is missing, you check if the output stuff is working (actuator, linkage). If everything looks good there, you probably have a faulty module. You can test this stuff in whatever order you think is most likely. Take some educated guesses to try and narrow things down quicker.

On 2000+ cars, it is easy to see whether the buttons are working in VCDS because the buttons connect directly to the ECU. But on AEB cars, the buttons connect directly to the Cruise Control Module, so you have to unplug the module and use a MultiMeter to see what's up. The module cannot be interrogated to fess up any informations.

[Trevman]

Alright, I was using this DIY Diagnostic - http://www.audiworld.com/forums/a4-b...n-long-168736/

And my first test of the pins in this test:

Ignition OFF, power to cruise OFF, multimeter on OHM setting:

1) Test between pin 5 (brown wire) and ground = zero ohms, if not, bad ground

2) Repeat for pin 1 if a brown wire exists (manual trans. and older models).

3) Test between pin 4 (red/yellow) and pin 8 (black/yellow) - infinite ohms. Press SET on CC switch = zero ohms. If not, bad CC switch.

4) Test between pin 10 (blue) and pin 8 (black/yellow), CC switch OFF = infinite ohms. Switch to ON = infinite ohms. Switch slightly in the direction of OFF, but don't click it over = infinite ohms. Switch to RES = zero ohms. If not, bad CC switch.

Between both pin 5 and ground and between pin 1 and ground the reading is not 0. Both read about the same right around 4.2 ohms. So apparently that means I have a bad ground. How do I fix that? Tried searching around a bit and didn't come up with anything. Maybe I'm looking in the wrong places

[Trevman]

Bump. I don't know where the cruise control harness grounds. Does anyone know? Based on testing above, I have a bad ground, but I can't figure out where that harness is supposed to be grounded...