Hello - I am new to both the forum and owning an Audi
I have an 2001 A4 Quattro with drive by wire. The cruise was not working when I purchased the car. After buying a CD manual I learned that I can't do anything without a VAGxxx. So I purchased the xtool and so far it works great.

Now for my issue, I can read the switch postion in the ecu for the cruise control, the switch works. I can also read the set mph this works as long as I am going under apx 45 mph (and the cruise works) when I go faster than 45mph the cruise will not set?? On a side note the mph in the data block is higher than the speedometer by about 12 mph??

Is there some programming setpoint to limit the speed of the cruise control?

Thanks for your help.

 

I did a little additional testing, the issue is not with the speed but with the gear, the cruise will not work in 5th gear(manual). But it works fine in 4th gear.
Does the car have a method to determine the gear? Maybe a mechanical switch? The mph difference between the data block and speedo could be an issue. I am thinking the cruise may work off of a rpm to gear ratio calculation instead of a straight speed signal, otherwise the speedometer should be the same as the cruise data block speed reference.

Any help or thoughts would be appreciated.

 

I wish I could help. I'm pretty good with Audi's extremely complicated vaccum cruise control on the cable throttle cars. But I've never worked on it on a DBW. But I will say this, on my 99.5 manual, there is no sensor to tell the ECU which gear I'm in. And I'm not sure why they would add that. If the ECU just compares RPM to vehicle speed it knows what gear its in. So your bad speed reading might have something to do with it.

You seem like a pretty good diagnoser, but is there any chance its just the switch on the clutch pedal?

 

Can't help you much, but I do know that the ECU calculates which gear you're in based on a function of the current RPM and VSS signal. Since your ECU VSS signal is off, I could see that potentially creating a problem where the RPM and VSS signals don't match up and the ECU can't tell what gear you're in.

There is a way to log the gear variable, but it's pretty complicated and involved, you can't just connect and press go.

 

Mine also has the same notorious cruise control issue, but it did randomly work in 5th gear the other day.....and that's the first time it's ever worked.

 

Thanks for the post, the clutch switch is working, I can see the data block change to the proper value with I press the clutch or the brake.

 

I think it has something to do with the speed not being correct in the cruise control data block, I am sure the ECU controls the speedometer as well so in theory the two values should match.

 

There's an excellent thread around here somewhere that explains the entire issue and how to fix it (with pics), but when I read it, I wasn't too worried about it, so I didn't subscribe to it.

 

A4TurboGuy - do you remember what the tread was about?(ECU, speedometer issues...?) I have searched the cruise control threads but I can't find anything on the DBW systems. There is a good thread on the older systems but unfortunately they don't apply at all.

Thanks

 

Thanks Mad Cow, I am a little confused as to why the speedometer would read differently than the cruise control block speed reading unless the speedometer is using a direct reading from the the VSS and the cruise is using a calculation, is there a document somewhere that describes how to log the gear variable?

Thanks