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Discussion Starter #1
Hi all

I’ve an odd problem on my 2006 TDI and the garage says it’s to do with my abs unit. It kind of trembles at 2000 rpm and the ESP light is always lit as off. The garage says it’s the ABS unit, they say it can be tinkered with but that they are damn expensive to replace.

Has anybody got one for sale?
 

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Discussion Starter #3

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Tinkering isn't something you do with ABS units. You either remove it yourself and send it away mail order for a cheaper test and repair then refit, or pay a lot more for the Stealer to do it. But don't underestimate the work and skills for a DIY job. If it's not a V.W garage they might be wrong and it sounds like they may want to further investigate and learn at your expense whereas the V.W Stealer may sound expensive but they are more likely to give a correct diagnosis which could be cheaper. Although £500 for anything seems normal these days. :(

Personally, I wouldn't pay a high price for a used car with warning lights showing.
 

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It kind of trembles at 2000 rpm and the ESP light is always lit as off. The garage says it’s the ABS unit
That sounds like two separate problems - if ESP is off then the ABS should be disabled and not affecting the rest of the car. I would want to see the results of a full fault scan, so get yourself an OBDeleven, VCDS, or some other VAG-specific diagnostic tool - or a friend who has one ;)

I tend to treat "the garage says" with a little skepticism when it comes to diagnosis. Unless they can show you an obviously broken part, the dealers are just following the instructions their computer walks them through and the rest don't have the assistance of a computer loaded with all the potential causes and diagnosis steps. If they can "show their working" then by all means trust them, but maybe don't trust them by default ;)
 

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That sounds like two separate problems - if ESP is off then the ABS should be disabled and not affecting the rest of the car. I would want to see the results of a full fault scan, so get yourself an OBDeleven, VCDS, or some other VAG-specific diagnostic tool - or a friend who has one ;)

I tend to treat "the garage says" with a little skepticism when it comes to diagnosis. Unless they can show you an obviously broken part, the dealers are just following the instructions their computer walks them through and the rest don't have the assistance of a computer loaded with all the potential causes and diagnosis steps. If they can "show their working" then by all means trust them, but maybe don't trust them by default ;)
I agree with all that. I would add that a dashboard ABS error might signify either a transitory problem which would mean the ABS is still functional, or a permanent problem which would mean that all ABS function is disabled, including stability control. Perhaps someone knows how to tell if all ABS function is disabled from the dash display without reading codes. In any case I'm not sure I'd like to be driving around in winter without being able to depend on ABS and stability control.
 

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I always thought the ESP and ABS functions were interlinked and there can be no guarantee one or the other may still work? There is very little info from the OP as to the nature of the fault. These systems have their own static and dynamic self checking. Static testing of the electronics is usually done at key on, then continuous testing is done when moving. ABS is usually very sensitive to any failure and keeping the ABS fault light off is always harder than putting it on! I assume the OP has turned on the ignition, watched the dash lights and confirmed the ABS and ESP lamps do come on briefly?

If warnings come on at key on failing the static tests, then something is clearly wrong. Dynamic self tests usually involve a continous check on the pulse count from each wheel sensor. If his faults only occur whilst moving I would have a look at those. But for somebody not wanting to spend money, intermittent wheel sensor faults are virtually impossible to find when something like vcds (or dealer diagnostics) can tell you exactly which wheel sensor of 4 is failing.
 

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I always thought the ESP and ABS functions were interlinked and there can be no guarantee one or the other may still work?
That's my assumption too. It was the trembling at 2000rpm that I thought would be a separate issue to the ABS/ESP problems.

I wonder if the OP could clarify whether the trembling occurs when the engine is around 2000rpm in all gears and when standing in neutral? Because if that issue was more to do with the speed of the car than the speed of the engine, it could point towards a wheel-related issue (e.g. the wheel bearing) which could mean both issues originate in the same area. That's a wildcard guess based on idle speculation, but worth following up on to rule out.
 

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Yes, that's why I explained the static and dynamic self checks done by the ABS system.

I know from from working on another ABS system that if one of about 60 printed segments on a wheel bearing with integrated sensor is faulty, the dynamic check will find the missing pulse. The OP says rpm but it could be wheel road speed related and the way to prove that is to shift to another gear at the same road speed and different rpm and drive hard around a left and right corner. And yes, it could be a worn wheel bearing or damaged wheel sensor. But as we know, a diagnostics scan will show those stored faults and say which wheel sensor it is. Front wheel bearings do more work than rear and if a scan points to a front wheel fault, it supports the argument.

I once had a vehicle with no access to diagnostics and figured out a way to test a printed wheel bearing ABS sensor. I put a masking tape reference mark on the tyre and wheel arch at 12 o'clock, then watched the sensor output on a 'scope as I slowly rotated the wheel by hand. I saw 2 missing pulses at 10 past 12 and 20 to twelve not present on the other 3 wheels. I would have seen the same thing with a voltmeter..
 
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