Aragorn

Ok i have a '96 1.8T A4 and i've been working on a retrofit of the factory cruise control system.

I've connected up everything as per the diagram from ETKA, and tested it all using the guide thats on here.

The cruise switch is working, as are the brake and clutch switches. The correct signals are present at the cruise ECU from the switch as per the instructions on the trouble shooting guide.

The pump itself pulls a vacuum when manually jumpered, and the valve also operates correctly when manually jumpered.

The problem is that it doesnt work. From the troubleshooting guide it suggests that with the cruise switch enabled on the stalk, the live to the pump (pin 7 on the cruise ecu) should go live once the speed is over 22mph. This doesnt happen. Pressing the set/resume etc switches do nothing.

Ive also tried two ECU's to rule that out, and both are the same.

Any ideas?

bmwbiker

Do you have a speed signal at the cruise control modual ? check per wire diagram. I beleave the signal starts @ 12v and goes down with speed increase

Aragorn

I'd been over the diagram many times and even moved that speed trigger as i was thinking along the same lines.

Turns out one of the diagnostic guides on here isnt quite right, which caused me to connect the brake light switch up incorrectly, i had the feed connected to the 12v side, rather than the bulb side, which basically meant the ECU assumed i was driving round pressing the brake all the time. Finally worked it out after using the more detailed diagnostic guide, and moved the wire to the other side of the switch.

The original ECU was also faulty, so once i moved the wire and swapped out the ECU, its all sprang to life