Cruise control on 1997 TD

[MF]

Help, somebody, please!
The cruise control on my 1997 TD Jetta has gone intermittent. It usually works only after I have driven the car for 1/2 hour or more (winter or summer) and then may quit for no reason. Often it will not work for days, then starts again.
Has anyone else found an answer to this problem?
Thanks

[Cheesetoast]

Remove trim cover over relay panel.
Unclip relay/fuse panel, unhook and drop it down as far as
it'll go.
Pull the door chime relay.. so it doesn't annoy the hell out of you.
Stick your head back there and shine a line back up from
the underside toward the front of the dash.  You'll see a white
and silver box next to each other.   The silver one is the cruise  ECU.
Pull the 12 pin plug from the back.

I simply cut some little pieces of thin solid wire (utility wire
found at any hardware store) and wrapped them around the ends of the
probes on my multimeter so that I could stick them into the harness slots
and let the probes hang.

Here's the reader's digest condensed version of the tests.
Probes on pin 9 and ground..  Turn on ignition and cruise control on stalk.
Should see 12V when on. 0 when off.    (tests voltage supply)

Probes on pins 9 and 4 (9 and 12 on some cars).  Ignition on, cruise on.
Should see 12V when on, 0 when off.    (tests ECU ground)

Probes on pins 8 and 4. Ignition on, cruise on, push and hold Set button.
Should see 12V when Set pressed, 0 when released (tests set button)

Probes on pins 5 and 4. Ignition on, cruise on. push and hold Resume button.
Should see 12V when Resume pushed, 0 when released. (tests resume button)

Probes on 3 and 9.  Ignition on, cruise on.  
Should see 12V.
Push Brake pedal.. should drop to 0. Release, returns to 12V. (tests pedal
Push Clutch pedal.. should drop to 0. Release, returns to 12V.   switches)

Probes on 7 and 4.. raise one front wheel and turn slowly.
Voltage switches between low (0-4V) and high (7-12V)
skip this one.. tests wheel speed sensors
and if you speedo works.. then this'll work too.

Here's the fun one..  
Out of the same type of solid wire, I made three little jumpers.
Jumper pins 9 and 11,  1 and 4,  and 2 and 4 (do 2 and 4 last so
you can pull it off and put back on easily) all at the same time.
Ignition on, cruise on, vacuum pump will run, and should push gas pedal
to floor.   You'll notice vacuum pump is *loud*.  
Cruise off, gas pedal returns slowly.. cruise on, pump on, gas goes back down.
Press brake pedal.. gas will return slowly.  Release, it'll go back down.
Press clutch pdeal.. gas will return slowly. Release, it'll go back down.

While it's all still running, pull the 2-4 jumper.  
Vacuum pump will stop.  Gas pedal should remain on the floor.  Wait.
Gas pedal should stay pressed to floor.  This indicates no
vacuum leaks.     Any of the above steps (cruise off, brake/clutch will
relieve the vacuum, and replacing 2-4 jumper will fire up pump again )

I did all that.  Every test passed. That indicates it's the Cruise ECU.
So just for giggles, I removed the trim panel under the steering
wheel (just 5 screws, and pull down), and that gives me access
to the 10mm nut which holds the bracket on with cruise and
alarm ECUs.  Removed.. unscrewed Cruise controller from
bracket, bent the tabs on the edges up, and pulled the
end off and the guts out.   Sure enough, there's a relay in there.
Everything looks perfect.  Nothing charred.   Futzed with the
relay's spring a little.. put it all back together..  

Went for a drive.. Cruise worked (first time in months).. for about
1 minute.  Then switched off and continued to be unresponsive for the rest
of the drive.  Got home, dropped the relay panel and ran the diags
again (took about 5 minutes the second time around, from start
to finish).  All tests passed again.   So.. We're back to the ECU being
bad.  That $235 circuit board that probably takes $15 to make..
Bah humbug.

[VentoGTD]

Brake switch in most cases.


:wink:






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