Cruise Control troubleshooting

[do.dah]

So much of my life is spent trying to diligently troubleshoot something and finding nothing glaring.
I put everything back together in defeat, and then find that the problem has magically resolved itself...
Mostly frustrating not knowing what/how/why, but over many years, I've come to begrudgingly accept the wins, deserved or not.....

[16CVs]

Spent part of the day fixing a clients Cruise control (4.5 hrs) I was my biggest enemy as I grounded a hot lead trying to follow the Flow chart in Bentley which is well thought out but sometimes as clear as mud.

I disconnected the Vacuum line from the T at the pump and ran a coupler between the two and checked that the brake light bulbs were good an they were.

I ended up with no light on pin # 2, the book said to check for a broken wire or bad connection. I broke out my continuity tester and checked all the wires front to back and they were all good. The Bentley should have directed us to fuse 18 as mentioned earlier as it provides switched power from the "G" circuit.

Once I had power to the black wire from the harness we took it out for a drive to test and found the brake switch to not be in adjustment and fixed it and still no love. We ran through the test and found everything working from the switches to the pump.

Feeling defeated we put it back together and the customer left, I figured I would come here and look around to see what was going on that I didn't see. Thinking that maybe the issue was the GW VSS which he had replaced as a possible suspect.

We were both going to ponder this, later in the day I got a call from the customer that on his way home while cruising on the freeway he tried it just fun and it came right on and worked like a dream. Holds a perfect speed and resumes properly and increases 2MPH with each tap of the set button.

While I am happy it works, I am not sure what I did to make it happed, he had spent a few hours previous running the tests and getting no where.

The moral here is don't give up, postpone the win and enjoy the victory when you get it.

Stacy
.
_________________
1987 Syncro Westfalia Triple knob (bastard)
1989 Syncro Tristar Triple knob "Swedish"
2013 Jetta Hybrid a true "Zwitter"
Samba member # 14980
Call anytime number 650 722 4914 .
Keep Your van running and upkept tastefully for the love of the hobby.
Don't let your van end up in an "abortions" thread.

[CoffeeAddict]

[davideric9]

I'm certainly no expert but from my reading of that diagram it looks like pin 3 of the main cruise control module is getting 12v power from C1 on fuse 2 and the pedal switches are normally closed,
_________________
1987 Syncro Westfalia, stock (bought 1994)
1986 Syncro Westfalia SVX, 3 knob (bought 2008)
1987 Westfalia (bought 2010)
1988 Wolfsburg GL (bought 2012)

[CoffeeAddict]

Thanks Busfixer.
I have incandescent brake light bulbs that do indeed provide the groundfpr this circuit. It turns out that the problem was with the troubleshooting guide in Benley (posted below).
In my opinion, the problem was that my Bentley troubleshooting instructions were unclear (at best) or incorrect (at worst). Bentley directs the user to put a test lamp between pin 3 of the CC module harness and a ground. However, doing that essentially connects the ground to the ground (ie no circuit). The correct test is to put the test lamp between pin 3 and a positive "+" ( or pin 1). The tests of the clutch and brake pedal switches can then be performed as described in Bentley.
I wrote to Bentley to ask them to clarify/ confirm, but I havent received a response.

[Busfixer]

Do you have LED brake light bulbs? If so, see my posts and Dodah’s fine solution. It worked for me. Cruise control was dead as a doornail until I made brake light mods.

Busfixer

[CoffeeAddict]

I have a new question for the group.
On page 27.29 of my Bentley manual (attached), the test for the clutch/brake vacuum valves indicates that the test light should be connected between terminal 3 (of the 8-pin cruise control (CC) module harness) and Ground. Then, with both the ignition and CC 'ON', the test light should illuminate (prior to actuating the clutch or brake switches). This implies that there's a 12V signal at the other end of the test circuit.
However, on page 97.177 (attached) there doesn't seem to be a 12V source available to power this test circuit. The 12V from fuse S2 (through C3) is only available when the hydraulic brake light switches are closed, that is, when the brake pedal is depressed. However, when the brake is depressed, it opens the mechanical vacuum valve switch and breaks the circuit. So, no joy on the test light illuminating prior to actuating the brake or clutch.
Is it possible that the 12V power supply for this test comes from fuse S18 through G2? If so, then the test light could be connected between terminals 1 and 3 of the CC module harness and then therefore be searching a ground to complete the circuit? And could that ground come from the brake light circuit, ie. when the BRK LT SWs are open?
I'm obviously missing a piece to this puzzle. Any comments would be welcome. Thanks.

[dirty-pierrot]

My cruise-control works now!!!
Some explanations, the issue was on the brake pedal switch, i adjusted the position before driving and the switch worked, i mean it was open when i press the pedal and close when pedal was released.
BUT, because of the vacuum of the servo-brake, the pedal goe down when driving, so the switch was open.
I adjusted the brake switch position with running engine, and now everything works

thanks everybody for your help, you were right, most of the time cruise-control issues comes from the pedal switch.

[16CVs]

Have you verified that you have the correct plug of the VSS? it is the same type of plug as that on the Brake warning plug just 3 inches away.

Stacy
_________________
1987 Syncro Westfalia Triple knob (bastard)
1989 Syncro Tristar Triple knob "Swedish"
2013 Jetta Hybrid a true "Zwitter"
Samba member # 14980
Call anytime number 650 722 4914 .
Keep Your van running and upkept tastefully for the love of the hobby.
Don't let your van end up in an "abortions" thread.

[dirty-pierrot]

Hi,
I double check everything on my cruise control system today.
from the ECU's connector :
-safety contact on brake and clutch pedal >ok (pin 3 and 8 )
(i use only the contact, the vacuum safety is removed)
-12 v on pin 1, ground on 8
-jumper between 7, 8 and 4, throttle go down and stay down even when jumper on 4 is unplugged> vacuum system is ok.
-on 5 and 8 VSS 1.14kohm maybe it's the issue should be less, I found exactly the same directly on the vss (rear of speedometer)
-ON/OFF, RESET and SET >12V on 1, 2, and 3 when activate on switch (checked also that there's no short circuit between those 3 wires)

So, it's look like it should work... but don't
I'm going to buy a new VSS

Thanks for your help
I hope my english is understandable

[dirty-pierrot]

[Howesight]

In my experience with the Vanagon, Audi and VW cruise control (CC) systems similar to each other, when the CC engages but then goes slower, the problem almost always is a vacuum leak.

Here's where to look:

1. The vacuum switches near the clutch and brake pedals: Sometimes they can be easily revived by replacing the O-ring inside. See this link:

https://www.google.com/search?q=Vanagon+cruise+con...9H8zQ,st:0

2. The vacuum pump - - sometimes the vacuum flap - - it's controlled by the CC module - - starts leaking and a new pump is then required.

3. Leaking vacuum hoses themselves. Usually these will develop cracks near whatever device they are connected to at the nipple.

4. The CC actuator itself can sometimes leak, but more often, the hose attaching to the actuator splits near the nipple and causes a vacuum leak.

So far as I can determine, the CC module is programmed to release CC if the vacuum pump continuously operates (as though there is a vacuum leak) for a set period of time.
_________________
'86 Syncro Westy SVX

[clamay]

[mathieux46]

Hi Dirty-Pierrot,

You can buy a new speed sensor from Gowesty, not expensive ( 35USD ) if you believe this could be your problem.

Thanks

Mathieu

[dirty-pierrot]

Thanks for your reply, the main problem is to purchase another vss to confirm or not the diagnosis.
My Cruise control was working perfectly but it started to be unstable, passenger were feeling the pumping on gas pedal and now it swithch on, gas pedal go down but start pumping and speed decrease.
I tested the pump, the switches on both pedals, everything works , so now, if i'm right, it could be the ECU or the VSS.

[RawUmber]

My VAG '321 907 344' VSS also measures ~1K ohm, and ~1150mH (inductance).

Higher speed generates higher AC voltage.

My understanding of the cruise control's VSS circuit is that the AC voltage you are measuring with your meter (Vrms) needs to be ~1.5VAC or greater to be measurable by the computer. In other words, if you see >=1.5VAC at the VSS, the vehicle/speedometer is moving fast enough for the computer to set the cruise control speed. Somewhere below that voltage, insufficient. I may be wrong!

Given that you observe the pedal being activated by the cruise control system, it suggests to me that the VSS working, so I am doubtful it is at fault. If you borrow/try another one, that should prove it.

[dirty-pierrot]

Hi all,
I have trouble withe the factory cruise control on my 1988 vanagon.
It can't maintain the speed when it switched on. I can feel the gas pedal moving but the speed decrease slowly.
I tested every component separately everything is ok, except the speed sensor, i measure 1.16 Kohm and it produce only 2 V AC when i turn the speedometer with an electic dril (needle at 80mph) from what i read on this forum the speed sensor should be between 90 to 110 ohm and should produce from 0 to 5V ac depend on the speed.
Can someone confirm that my speed sensor is the problem ?
It's no longer available from VW is there another reference who could be use instead?
thanks and regards

[Busfixer]

Good info Dodah - I don't recall getting this info from Van Cafe. Might go back to my hi-tech LED brake lights!
Thanks, Busfixer

[do.dah]

[Busfixer]

Dodah - what model year and transmission do you have? I have a 1988 with manual transmission. Just speculation but there are several different cruise control wiring diagrams for different model years and transmission types. Perhaps some are susceptible to brake light impedance and some not?