ArandA4

All, I'm in the middle of doing this and writing it up and thought I'd throw it out there for your viewing pleasure. I haven't performed all of the electrical testing, so things will most likely change. In the meantime, if somebody has done anything similar or if you know of anything that is clearly wrong, please let me know.

So far, I think the problem with my CC system is in the CC set switch.

Cruise Control Diagnostics

In the Non-DBW A4 (96-99.5), the cruise control (CC) system is a mechanically-actuated, vacuum-driven, feedback system. The CC system, while not overly complex, has a history of being flaky, intermittent, and downright problematic. Many owners have had warranty repairs done on various parts of the CC system. As the last of the 99 models exit the warranty period, more and more non-DBW A4 owners are going to be faced with CC failures that won't be fixed for free by the dealer. Hence, the need for some general diagnostic procedures to pinpoint problems and reduce repair costs. I found the skeleton for this write up on the www.20v.org website (with special thanks to Joe Yakubik), but it was directed towards older model Audis. I have adapted it based on A4 wiring diagrams and system configuration.



The cruise control (CC) system consists of four major components.

Vacuum System (including pedal switches, pump, and actuator)

This is a common source of problems. For testing, you'll need a way to generate and hold vacuum in the lines. A good tool for this is a miniature Mity-Vac type of device although the same result can be achieved by pushing inward on the actuator diaphragm.

Wiring

Most common WIRING problems in this circuit occur in the wires going from the steering column, down the turn signal arm, and into the switch. There is also wiring for the vacuum pump that may need to be checked.

Steering Column Switches

From the AW archives, it appears as though this is the item that is most frequently replaced by the dealer under warranty.

Control Unit

This piece rarely goes bad, so it should only be suspect when all other common problems have been ruled out. The easiest way to test it is to put in a known good unit.



Cursory Troubleshooting

First, check the obvious. Blown fuses? Check brake light fuse 13 (and CC fuse 31 on cars with manual transmission). If the brake light fuse is blown, neither the brake lights nor the CC system will work (call me Master of the Obvious). Also, try replacing fuses with brand new ones. In the past, I've had fuses that looked fine, but simply didn't transmit enough current to turn anything on. In the engine compartment, check the actuator linkage bushing and make sure the actuator is still physically coupled to the throttle. Also look for any disconnected vacuum lines in the engine compartment. If you can't find the problem, more in-depth troubleshooting is required.



Vacuum System

Disconnect the vacuum line at the pump (which is located under the ABS unit). The tube coupled to the pump is a short length section that ends at a T-fitting. The tube on one end of the T leads to the actuator and the other goes to the vent switches coupled to the brake (and clutch if equipped). With a Mity-Vac apply vacuum to the system. The bellows should move the throttle a bit (nowhere near WOT) and stay until you release vacuum. Without a Mity-Vac, depress the rubber part of the diaphragm and plug the other end of the hose. It should stay put. Repeat this test and depress the clutch pedal, and again with the brake pedal. The vacuum should always release as soon as you touch the pedal. This will show whether you have a bad switch at the pedal, or a leaking line, or a bad actuator diaphragm/bellows.

To see if the vacuum pump is operating correctly, it is easiest to remove it. (Note: You might also be able to test the pump from under the dash, but that involves pulling the glove box and disconnecting the CC control module connector. See wiring system below. However, it is easier to visually verify throttle movement if you do this under the hood.) The service manual says you can remove the pump after removing the left-front wheel housing liner, but on my 1.8T, I was able to snake it out through the hole between the ABS and power steering reservoir (after removing the black reservoir cover). There are two nuts holding the pump bracket to the ABS support bracket.

To test the pump, you'll need three test leads with female blade connectors (like speaker connectors) at one end. Coupled to the pump, there should be a three prong electrical connector, a small hose that connects back to the pump, and the main vacuum hose. Following the leak test, put all vacuum hoses back in place and disconnect the electrical connector. 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 pump vent is the left upright. (My pump had a diagram that had 15a for the power terminal, P for pump ground, and V for vent ground.) Look on the electrical connector to make sure: blue/red wire is +12v, brown/red is the pump ground and green/blue is the vent ground. Using your test leads, connect +12v to the power terminal and connect the pump ground and vent ground terminals to chassis ground.

When you have power to the pump and vent, 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 vacuum to operate. Note that if you ground only the pump and not the vent, the throttle will move slightly to some final point nowhere near full travel and will close when you disconnect the pump from ground.

If

a) your vent is closed,

b) your pump runs, but

c) your throttle doesn't move or doesn't reach WOT and

d) you have no vacuum leaks,

the lines may be clogged. Check the hoses and flush them or replace them as necessary. It is also possible that the pump may be clogged. The pump intake (the larger black port) and the exhaust port (the stubby white one with a flange at the end) are located on a flat disc-shaped flange that covers the pump diaphragm. I discovered after yanking on the vacuum tube that this flange comes out. You might try removing this flange and checking for obstructions. If everything appears unclogged, the pump may simply be defective. If all the above checks out, then you have isolated the cruise problem to the electrical side.



Electrical System

There are two procedures here. The first is derived from an older Bentley manual, the second is an alternative method. The advantage of the Bentley procedure is that 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 foot well on the passenger side.



Bentley Method:

To test the electrical system you need access to the control unit; it's up under the dash on the passenger side. You don't need to remove the dash, but you will need to pull the glove box. If you know what you're looking for, you may not even have to remove the glove box. Simply rotate the glove box down after detaching it from the guides on either side. The control unit is high in the dash and has a brown 12-pin connector attached to it. Part number for the control unit is 4B0 907 305. Disconnect the connector and pull it down to check the following.

Note: The connector has 2 rows of contacts: 1-6 and 7-12. Pin 1 adjacent to pin 7 and pin 6 is adjacent to pin 12. Positions 2 & 3 are not used. Pin 1 may or may not be used depending on your model.

Note also: There are FOUR (4) switch positions in the CC stalk switch. The electrical positions correspond, from left to right with RES, ON, COAST/DUMP, and OFF; not simply RES, OFF, ON. SET is a separate push button switch on the end. The COAST/DUMP position is a temporary position like RES. It is to the right of ON, between ON and OFF, on the left side of the hard click.



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.



Ignition ON, cruise ON, multimeter to Volts DC:

5) Test between pin 11 (red/green) and ground = 12V, if not bad fuse 13, bad brake light switch, bad brake vent switch, (bad clutch vent switch), or bad CC switch. Need to access CC switch terminals to further diagnose.

6) Test between pin 11 and pin 5 (and/or pin 1) = 12V (re-checks power and ground in CC circuit).

7) With 5) above still connected (pins 11/5), press brakes = 0V, if not brake vent switch.

8) Repeat for clutch if applicable.

9) With 5) above still connected (pins 11/5), shift the CC switch to RES = 12V. Switch slightly in the direction of OFF, but don't click it over = 0V. Switch OFF = 0V. If not, bad switch.

10) Test between pin 8 (black/yellow) and pin 5 (or ground and/or pin 1), CC switch OFF = 0V. Switch to ON = 12V. Switch slightly in the direction of OFF, but don't click it over = 12V. Switch to RES = 12V. If not, bad CC switch. Same for Automatic Transmission? Can somebody verify this step for Auto. Transmission? On the manual transmission, the signal getting to pin 8 comes from the battery (via fuse 31), but for the auto. transmission, the signal comes from the transmission.



Pump wiring check, Ignition ON, cruise ON, multimeter to Volts DC: MAY REQUIRE 22 MPH

11) Test between pin 7 (blue/red) and pin 5 (or ground and/or pin 1) = 12V.

12) Jumper between pin 6 (brown/red) and pin 5 (or ground and/or pin 1). Pump should run (checks pump/wiring).

13) Jumper between pin 12 (green/blue) and pin 5 (or ground and/or pin 1). Valve should click (hood open helps to hear it).



Alternative Method:

This method more effectively isolates the switch and doesn't involve being upside down, on your back. This 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. However, be forewarned, it does require pulling the steering wheel and airbag.

To disable the ABS, the front wheels must be straight and disconnect the negative battery terminal. Make sure you route the loose battery cable so that there's NO CHANCE of touching the - battery terminal. Some might suggest letting the car sit for 15-30 minutes after disconnecting the battery (to discharge any storage devices, i.e., caps), but the service manual says work can begin immediately after disconnecting the battery.

PLEASE BE CAREFUL AND FOLLOW APPROPRIATE AIRBAG REMOVAL PROCEDURES! Better safe than exploding!!!

As for removing the airbag and the steering wheel, the service manual includes no less than 4 different procedures dependant on model year and whether the sport steering wheel is installed. In general however, the airbag is secured to the steering wheel by two T-30 TORX bolts that can be accessed from the rear of the steering wheel. After removing these, the airbag should come off. Disconnect the connectors as appropriate and place airbag on a solid surface with the bag side facing UP. The steering wheel is held in place by a large hex nut, hex bolt, or (most likely) a triple square bolt (12 point). Once removed, the steering wheel should slide right off. Once the steering wheel is off, the steering column covers can be removed to access the CC switch.

The following guide will identify which wires go where. You'll be checking the function of the switch. Use the wiring from the mating connector to ID which pin is which. These are different pins than at the ECU, but some of the wires may be the same. When testing, be careful not to short the meter at the pins, there's not much room back there.

Pin 1 = Red/Grey

Pin 2 = Blue

Pin 3 = Red/Yellow

Pin 4 = Black/Yellow

Pin 5 = Black/Blue (Manual) or Green/Red (Automatic)

Pin 6 = Red/black



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/OFF/RES = infinite/open. Switch to SET = zero/closed.

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 access to the Bentley wiring diagrams, you can see that there are more permutations, but this checks the important ones.

ArTT Vandelay

Dude, that is an awesome write up. Make sure to send it to tech!

ArandA4

I'm sure that in the interim, the write up will change. Also, everybody please feel free comment/correct where appropriate.

amwafa

I have a '98 A6 Quattro 2.8L, and the cruise control has been out for I-don't-know-how long. So far, I checked all fuses, both the brake light switch and brake vent switch (all are good and have proper resistance with respect to their positions...according to Bentley), checked the vacuum system for leaks (none), and checked the cruise control switch at the steering wheel. When I opened it, the wires to the switch were burned (I have the switch that combines the signal, high beam, and cruise buttons into one single switch). Before it went out, though, I was able to hear the relay in the CC computer (under the dash on the passenger side...4DO 907 305). Then one day, the clicking stopped. I replaced the CC switch on the steering wheel, and I heard the relay clicking again, but from fear of the new switch burning out, I turned the CC off. I did electrical tests according to this post: https://www.audiworld.com/forums/sho....php?p=1214628. However, when testing voltage between pin 11 and pin 5 (pin 5 is ground...also touched the body of the car with the multimeter to make sure I had proper ground) from the CC computer plug, voltage was found to be .003 (should be 12V, and the multimeter confirmed 12V on a battery I had lying around, so it's not the multimeter's problem). My question is, what could prevent proper power from reaching the CC computer while still allowing the relay in the CC computer to click? Also, what could have caused the switch to burn?

dannyhugo28

First off, beautiful write up. Second, this is kind of a dig, but it's worth a try. I went through every piece of this testing everything and more. The results concluded that everything is working the way it should except that my CC module isn't getting 12V when it should. In fact, it gets 12V when it very much so shouldn't. I shot the issues down to the point that it had to be either one of the vent switches, brake light switch, or the stalk. Tested the stalk, and it's good. Shortly after, by some form of mistake, I found out that the CC module got 12V when the brake light switch was fully extended, meaning that it is only getting power when pushing the brake pedal. Replaced the switch to no avail. Any info on what could be causing such a strange issue or possibly something I'm missing? Thanks.

dufftime

I know this thread is ancient, but just wanted to say a huge THANK YOU. I had given up on having a working cruise control again but got it working by cleaning out the copper on the CC switch.
If anyone is reading I have the following tips:

1. There are 3 clips shaped like a number 7 that hold the plastic housing onto the steering column. Just bend them out to release.
2. It's a torx 6 (T6) to remove the 2 screws that hold the wires to the main block shown here: http://www.rsquattro.net/repairdocs/...h_Repair_1.JPG
3. Make sure your battery is disconnected before you reinstall the air bag or else you will trigger the Air Bag light. You need VAG COM to reset it.