Cruise Control Pulsing

ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
Hi all,

I have a strange issue that has recently developed on my 2011 Golf MK6 1.6 TDI. If I set the cruise control at a speed between 40-50mph (around 2000rpm), the car seems to surge every couple of seconds, like blipping the throttle to the desired speed, backing off by less than 1mph then blipping again back to set speed and again backing off, repeating every 2 seconds or so... Gets more pronounced when going downhill and then reaching level ground. Never had this before on my other VWs. I can't replicate it with the cruise off when travelling at a set speed so can only attribute this to the cruise control or some erroneous data it's getting. There are no fault codes showing up in VCDS.

I was thinking this could be a vacuum leak somewhere within the cruise system to the throttle but having done some research it appears the cruise system communication is all electronic (no movement of the pedal). Does anyone else have any idea what the source of this issue could be? I am a bit stumped as it doesn't happen under manual conditions (no jerking).

Thanks.
 

Ol'Rattler

Top Post Dawg
Joined
Jul 3, 2007
Location
PNA
TDI
2006 BRM Jetta
Something you could try would be to set the cruise and push the accelerator to just shy of the cruise set point and see if that makes any kind of difference in the surging.

If it does, it could mean that the accelerator variable resistor has a flaky electrical connection or a defect.

There may be some measuring blocks you could monitor with VCDS that might give you some kind of clue as to what the CC is doing.
 

ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
Something you could try would be to set the cruise and push the accelerator to just shy of the cruise set point and see if that makes any kind of difference in the surging.

If it does, it could mean that the accelerator variable resistor has a flaky electrical connection or a defect.

There may be some measuring blocks you could monitor with VCDS that might give you some kind of clue as to what the CC is doing.

Hi,

Thanks for the reply. Unfortunately accelerating past the cruise set speed and allowing it to settle back has no effect on the issue, it returns. Measured accelerator position in advanced measuring blocks and it looks fine.

What is strange is that this issue only happens below 50mph (up to 2000rpm), or at least it's only noticeable at lower speeds... If I go 70mph I have not experienced it.

Anyone else experience it or have an idea what's causing it?

Thanks.
 
Last edited:

ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
ok, slight update this pulsing/fluctuating is noticeable at 70mph too. The rpm going up or down during this 'blip' is negligible on the display but I feel the surge and drop through the seat, perhaps once every 2 seconds or so.

I have been looking at the vacuum pipes and they seem fine with no cracks. And am I right in thinking to rule the EGR and Turbo out as the symptoms don't appear during non cruise control driving :confused:
 

ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
My old diesel Mercedes did the same thing! It was a vacuum leak...
Hi there,

Thanks for this. I did think that but can't see a leak and understand that the Golf MK6 cruise does not operate from the vacuum. If I am wrong though, please correct me and I will revisit the engine bay ;)
 

piotrsko

Veteran Member
Joined
Aug 11, 2013
Location
Reno Nv
TDI
2013 Golf, 2000 F-250 (7.3)
If it was my ford, I would suggest the VSD sensor on the tranny is going bad as you have typical symptoms with no DTC showing. However, I'm new to computer diesels in VW's and not sure how they get vehicle speed data.
 

lou95gts

Veteran Member
Joined
Sep 24, 2010
Location
Caledon
TDI
2010 Jetta
With my car it was the left front ABS sensor. Its information is also used for your speedo and cruise. Did you change a lh front wheel bearing lately? The cheap bearings have bad impulse rings and will give this result.

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ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
With my car it was the left front ABS sensor. Its information is also used for your speedo and cruise. Did you change a lh front wheel bearing lately? The cheap bearings have bad impulse rings and will give this result.

Hi, thanks for this idea. I did have the front right coil spring changed about 2 months ago and can't remember it doing that beforehand. I will check some 'on the road' readings from the abs sensors and report an update, but I thought that any anomalies might have thrown a fault code which aren't there... Worth checking though for sure! Thanks.

I will let you know how I get on, thanks.


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lou95gts

Veteran Member
Joined
Sep 24, 2010
Location
Caledon
TDI
2010 Jetta
No fault codes with erratic abs sensor output. I was able to see my front lh reading vary a few mph at a steady speed.

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ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
No fault codes with erratic abs sensor output. I was able to see my front lh reading vary a few mph at a steady speed.

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Hi, went for a drive measuring abs speed output on all 4 wheels via VCDS. Whilst at a steady straight ahead speed, the 2 front sensors varied by +/- 1km/h (would change every 2 seconds or so) whilst the back stayed at the set speed. Perhaps this is pretty normal, or could it be enough to warrant the cruise pulsing I wonder. If anyone can check against their cars that would be great. Thanks.
 

ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
Hi again,

I have managed to put the VCDS log of the abs sensors into a chart, located HERE. As can be seen, the front two vary by about 1kph quite regularly.



I am wondering whether anyone else has done a log of their ABS Sensors and whether such a differential on the front sensors is normal, so I can eliminate this as being the cause of my unsettled cruise control :( Thanks.
 

lou95gts

Veteran Member
Joined
Sep 24, 2010
Location
Caledon
TDI
2010 Jetta
I didn't log my sensors but that is not normal. They should be rock steady. From what I understand, the front left is the one used for speedo and cruise so it needs to be right. It took a hub replacement on my car to fix it. I tried a new sensor first but it didn't correct the problem. Unfortunately the abs sensors are specific to their location and cannot be swapped left to right or front to back for trouble shooting.

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ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
I didn't log my sensors but that is not normal. They should be rock steady.
Hi,

Thanks for this. I was wondering why both front wheel sensors might vary by 1kph... I could understand the front left only doing it and this leading to the cruise going haywire as a result. But nonetheless the change if abs sensors or hub is definitely worth it to see if it makes any difference, providing I can get a log of another similar vehicles abs sensors at speed and they are rock steady... Perhaps if mine are faulty they are not faulty enough to warrant tripping a fault code, who knows...

Would anyone with access to VCDS mind logging the data from measuring blocks 1 in the abs control module please and uploading the cab file, so I can compare against my data?

Thanks.


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ukguy

Veteran Member
Joined
Jul 27, 2004
Location
Manchester, UK
TDI
VW Golf MK6 1.6 TDI Bluemotion Match
Today I disconnected the front left abs sensor, went for a little drive, even though fault in abs on dashboard, speedo and cruise still worked?? Then removed and cleaned both front abs speed sensors, went for a drive and still same issue with cruise pulsing. Rears abs sensors look a lot more stable than the front so never bothered cleaning them. Now wondering which sensor feeds the speedo and cruise...


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