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Cruise repairs, very long
I don't have the address of the original poster. This is a long treatise
on cruise troubleshooting. It applies directly to the 200's, but probably
applies to the V8 and other Audi's, as well.
RE: Cruise repairs, long
A '91 200q with no cruise? Sounds familiar!
First a few questions:
Do you have:
the Bentley for your car
some test leads?
After my rather frustrating battle with my cruise I'll narrow the cruise
control system down to four sections: vaccuum, switch, wires, and control
The control unit is probably okay. I blamed mine for some problems, but it
was fine. I used a spare to check mine, and even after some fairly rough
treatment, the spare worked.
The vaccuum system is a common culprit, but if you have a Mity Vac, is the
easiest to check. You can do it without a Mity-Vac as well, it's just a
tiny bit harder. I bought mine at Walmart's for $20ish.
Depending on your perspective the wires might/might not be a problem.
There are two and one-half arms or electrical branches. One goes to the
vaccuum pump, the other to the switch. The "half" arm goes from the
connector on the back of the steering wheel, down the arm to the switch.
This arm is a problem. I've had cracked wires here twice. My recommended
procedure to check this arm is at the end of this post.
The switch (perspective again) is simple, but the switch includes the
wiring going up the arm.
To start trouble shooting:
Fuses first, check #3 and #12. Bentley also says check brake lights. The
system uses the ground reference of the light control unit to see if the
brakes are on.
Disconnect the vaccuum line at the pump (just behind/under the coolant
reservoir). With a Mity-Vac apply vaccuum to the system. The bellows up
under the injectors should move the throttle and stay until you release
vaccuum. Without a Mity-Vac, depress the rubber part of the reservoir and
plug the other end of the hose. It should stay put. You can repeat this
test a few times, depressing the clutch, then repeating, depress the brake.
The vaccuum should always release. This will show whether you have a bad
switch at the pedal, or a leaking line, or a bad bellows.
To see if the vaccuum pump is operating correctly, it is easiest to remove
it. You can also do this from under the dash, but that involves pulling
the glove box, a PITA.
Carefully move the coolant reservoir out of the way, there's a main hose on
the bottom, in addition to the low level sensor, then remove the vaccuum
pump. There should be a three prong electrical connector, a small hose
that connects back to the pump and the main hose.
Put all vacuum hoses back in place and disconnect the electrical connector.
Using your test leads, connect ground and +12v to the pump and solenoid
switch. If you are looking at the connector on the pump like a "U", power
is the right upright, the pump is the crossbar, and the valve is the left
upright. Look on the electrical connector to make sure: blue/red is +12,
brown/white is the pump ground and green/blue is the vent ground.
When you have power to the pump and valve, with the hoses connected; the
throttle linkage should move. If you disconnect ground from the pump, the
throttle should stay put. Disconnect ground from the vent and the throttle
closes. If you get full travel on the throttle, then your pump draws
sufficient vaccuum to operate. If all the above checks out, then you have
isolated the cruise problem to the electrical side.
If your throttle doesn't move but your pump runs and you have no vacuum
leaks,read on: If you have a Mity-Vac or a vaccuum gauge, you can get a
numerical value for the pump.
A year or so ago, my pump worked fine. This time around it drew 3 inches
Hg. I disconnected the hoses, and connected a line to the air intake (the
larger black port). I also connected a return line to the exhaust port
(the stubby white one under the intake). I plugged the vent port with my
finger, stuck the intake hose into some water, and applied power for 3-5
seconds. After this I ran it disconnected to flush the water out. After
the flush I got 17 inches Hg out of the pump. I can't guarantee if there
are any long term negative effects of this method, but it saved buying a
new pump in the short term. (Six months later it still works)
Electrical troubleshooting comes next, Bentley procedures are directly
below, mine are way below.
You can take my recommendation, or follow the Bentley/Audi procedure. I
bet if the system doesn't work it's either the vaccuum or the switch wires.
The advantage of the Bentley/Audi procedure is you may not need to remove
the airbag to IDENTIFY the problem. The disadvantage is you will probably
have to remove it to FIX the problem. This is in addition to squirming
upside down in the pax footwell.
Re: Bentley, to test the electrics you need access to the control unit;
it's up under the dash on the pax side. You don't need to remove the dash,
but you will need to pull the glove box and a trim panel or two. Push the
A/C duct out of the way and remove the connector off the ECU. Contrary to
Bentley, there are two: one an eight pin connector, and a single ground
connector. Pull the eight pin connector down and do the following:
Ignition OFF, power to cruise OFF, multimeter on OHM setting:
1) Test between pin 8 (brown wire) and ground = zero ohms, if not bad
2) Test between pin 3 (black/red) and ground, press brakes = infinite
ohms, if not bad pedal
3) Repeat test with clutch pedal.
Ignition ON, cruise ON, mm to Volts DC
4) Test between pin 1 (blue/red) and ground = 12V, if not bad fuse (power
5) Test between pin 1 and pin 8 = 12V (re-checks power and ground in CC
6) With 5) above still connected (pins 1/8), shift the CC unit slightly in
the direction of OFF, but don't click it over = 12V, if not bad switch
(checks half of a little documented "dump" or "coast" function)
multi-meter back to OHMs
7) Test between pin 3 and ground, switch CC ON/OFF. ON = zero ohms, OFF =
infinite ohms; if not then bad switch.
8) Test between pin 3 and ground, switch CC from ON in the direction of
OFF, but don't click over. Should go from zero to infinite and back, if
not then bad switch. (tests the other half of the "coast" function)
9) Test between pin 3 and ground, switch CC to RES. Should be zero ohms,
if not then bad switch.
10) Test between pin 6 (blue) and ground, switch CC to RES. Same as 9).
11) Test between pin 2 (red/yel) and ground, switch CC to SET. Same as 9).
12) Jumper between ground and pin 4 (blue/white). Pump should run (checks
13) Jumper between ground and pin 7 (green/blue). Valve should click
(hood open helps to hear it).
ALTERNATIVE METHOD, MY RECOMMENDATION:
This requires nimble fingers and a little more delicacy, and won't test the
wiring from the pump to the ECU or the switch connector to the ECU or the
electrical switches at the pedals. It more effectively isolates the switch
though and doesn't involve being upside down, on your back.
Everything off, you could pull the negative battery terminal to avoid
honking the horn.
Remove the upper cover for the steering wheel. The CC wiring comes down
the stalk and comes up over top, left side of the steering wheel switches
and goes to a six pin connector. If you remove the steering wheel it's a
lot easier; but is not absolutely necessary. I recommend it, anyway
because you will probably need to do it to repair the switch wiring.
FOLLOW TO THE LETTER THE AIRBAG REMOVAL PROCEDURES. Better safe than
exploding!!! I've done this three times without a hitch.
You may get lucky and see a broken wire or two in the bend from the stalk
to the connector. The wires are wrapped in tape, though; so it may look
The following guide will identify which wires go where. You'll be checking
the function of the switch. Use the wiring from under the dash to ID which
pin is which. These are different pins than at the ECU, but pins 2, 3, and
5 are the other ends of the same wires.
Pin 1 = Black/yellow
Pin 2 = Blue
Pin 3 = Red/yellow
Pin 4 = Black/blue
Pin 5 = Blue/red
Pin 6 = Red/black
Find pin 4 on the steering column connector, it provides power to the
system and distributes it to the others. When testing, be careful not to
short the meter at the pins, there's not much room back there.
Multimeter to OHMs
1) Test between pin 4 and pin 5. Switch OFF = infinite/open. Switch ON =
zero/closed. Switch from ON in direction of, but not OFF = zero/closed.
Switch to RES = zero/closed.
2) Test between pin 4 and pin 2. Switch OFF = infinite/open. Switch ON =
infinite/open. Switch from ON in direction of, but not OFF =
infinite/open. Switch to RES = zero/closed.
3) Test between pin 4 and pin 3. Switch ON = infinite/open. Switch to SET
Find pin 6. This gets the signal from the braking circuit.
4) Test between pin 6 and pin 1. Switch OFF = infinite/open. Switch ON =
zero/closed. Switch from ON in direction of, but not OFF = infinite/open.
Switch to RES =zero/closed.
If you have the Bentley you can see that there are more permutations, but
this checks the important ones. You can also see that there are four
switch postions in the stalk switch. The electrical positions correspond,
from left to right with RES, ON, coast/dump, and OFF; not as posted as RES,
OFF, ON. SET is a separate function down on the end.
If you do find a broken wire in the stalk, it is easiest to replace the
wiring completely. In an interim, unsuccessful, repair I did successfully
leave everthing in the car and added a separate "plug" connector from a
computer on top of the column switches. This connector fixed an electrical
problem, but I hadn't diagnosed the weak vacuum then. If you do remove the
column switches to rewire the switch, take the following advice:
Be careful opening up the switch. There's a spring and a roller
bearing-thing that jumps out.
Find six strands of very thin test lead. It maintains its flexibility
Each strand should be at least 4 - 6 inches longer than the original.
Wrap all six strands in teflon plumbers tape.
Push this bundle through the stalk from the base towards the end. Trying
to route the cable the other way is a PITA.
Solder (very carefully) the switch portion first.
Snug the re-assembled switch in the stalk, then snip the wires to the
Solder the pins for the connector last.