# How to repair G200 and G251 sensors



## John-H

*How to repair G200 (Roll - lateral) and G251 (Pitch - longitudinal) sensors*

These are the sensors for the ESP system which detect acceleration / braking or g-force in a longitudinal direction (pitch) or sideways g-force on cornering (yaw). Both are single axis acceleration sensors and both the same part (1J0 907 651 A) but just mounted differently - one 90° to the other. The lateral (yaw - G200) sensor is mounted under the steering column and the longitudinal (pitch - G251) is mounted behind the glove compartment on RHD UK Mk1 TT vehicles.

See here for a guide by shaneg for removal: Lateral-G200-Removal. The removal of the other sensor behind the glove box is similar and shown here: Longitudinal-G251 Removal .

Note that this repair guide doesn't cover the later combined sensor G419.

There are a couple of guides in German here: G200-251-Link1 and here: G200-251-Link2 which are good for the pictures at least if you can't read German. All credit to them for delving into the units, finding the fault and posting the information.

Fortunately Dani (A3DFU) speaks fluent German and has kindly provided a couple of handy translations into English - much better than using Google transation!

View attachment G200-251-Link1-English.doc

View attachment G200-251-Link2-English.doc


*Notes on diagnosis and repair.*

*Diagnosis:*

With an ESP light showing and Vag-Com reporting a G251 longitudinal sensor with an implausible signal I tried zeroing the sensor using Vag-Com. Here's an excellent guide by Tony Rigby: G200-251_Read_and_Reset_Guide

*N.B. When using the above recalibration procedure G200 will "zero" to 0m/s but G251 will "zero" to 24m/s and report a successful reset within perameters if all is working.*

Unfortunately the sensor was reading a constant too high a value and could not be reset so needed replacing or repairing. I needed to first ascertain which of the two positions (steering column and glove box) the sensor was located. There seemed to be scope for confusion.

The lateral sensor G200 was reading near zero and in order to double check the good one is not about to be removed - if you reach up and twist the good sensor on its bracket a little you can see the reading change slightly. This is reassuring and a good check. The faulty sensor won't respond. If you unplug the faulty sensor the reading will change but to another fixed offset - also confirming you've got the correct one.

*Repair:*

Having read the translated guides I thought I'd add some comments of my own with some pictures from repairing A3DFU's longitudinal sensor.

Firstly you need to gouge out the silicone rubber potting compound. This is best removed with your thumb nail or a plastic implement rather than a metal screwdriver to avoid damaging components or scratching through PCB traces. Some IPA will help loosen the bond as the material is rubbed away with a wooden cocktail stick or similar and help to clean the PCB. Dig away round the edges of the PCB too to help undermine it using something sharp.










You then need to de-solder the three connector pins. This is best done with vacuum desoldering equipment but you can use de-soldering braid. Whichever way, make sure the pins are completely loose in the holes by checking they can be moved sideways with your fingernail.










You can then prise out the PCB being careful not to damage anything. Having removed the PCB you will probably find the chip is still embedded in the potting with its legs showing. Carefully cut around it and prise it out too


















With the chip removed I did notice that the pins han no solder on them. The PCB had little solder. The pins on the chip looked like stainless steel in appearance although I later confirmed they were nikel/tin plated copper.


























It did seem likely that the cause of failure was too little solder combined with vibration and muvement with thermal expansion and contraction over the years that had caused fatigue of the tiny amounts of solder holding the chip to the PCB. Poor solder flow due to lead contamination or poor flux could also be an issue The early days of lead free solder production were plagued with this sort of thing.

Here's the chip cleaned up.










Before re-soldering the chip it's a good idea to clean the pins using some abrasion to form a key and break through any surface contamination and oxide. A glass fibre pen is being used here although careful use of a small piece of wet and dry paper would do.










Make sure the dot on the face of the cuip (pin 1) is nearest the semicircular PCB cut out and carefully solder back into place but using a more generous amount than in original manufacture so it's mechanically stronger.


























Inspect the other compoents with an eyeglass for poor soldering but in this case it they were all fine. I suspect the only problem was with the chip.










Before replacing the PCB, excavate more of the silicome potting from around where the chip was in order to allow new potting to flow around the chip and PCB and not have problems with fitting. Then replace the PCB firmly on it's mounting pegs and re-solder the connector pins.










Here I'm pouring in a suitable two part mix silicone rubber potting compound designed for this purpose. If you have access to vacuum equipment you can also remove all the trapped air so when atmosphere is allowed back in the silicone will shrink down and have no voids.










If you don't have the correct potting material and equipment you could instead use silicone bathroom sealant or similar but this is not the best due to it being an acetic ure requiring moisure in the air so may take some time to go completely solid. In one of the German guides someone used hot melt adhesive. This will probably work too but will not bond as well to the existing potting.










The reason the potting is there is not so much to prevent moisure from entering but to form one solid inertial mass and prevent unwanted vibration in the sensor. I don't think its there to hide the simplicity of a £200 part either!

When set completely the sensor can be returned back to the car and the reset procedure applied.


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## steveupton

Excellent guide, as usual the explanation and detail makes it very professional and more importantly, easy to understand. Wish it had been around a couple of years ago when replaced this sensor in my step sons TT!

Just shows how much of a rip off Audi parts can be, manufacturing cost must be a very small fraction of what they charge.

Does the G419 in the later TT's not suffer from the same problems then?


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## brian1978

[smiley=cheers.gif]


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## Wak

Excellent Guide John, but annoying about the construction quality looking at that chip as you say barely any solder on the pins not great quality and one could argue designed to fail. :?

The Repair looks like it will last forever.


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## cookbot

Wak said:


> Excellent Guide John, but annoying about the construction quality looking at that chip as you say barely any solder on the pins not great quality and one could argue designed to fail. :?
> 
> The Repair looks like it will last forever.


Could also be the use of lead free solder that the eco hippies want to be used. All well and good except it's brittle and components don't last as long, thus ending up on landfill! Lead based for the win :lol:


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## Wak

cookbot said:


> Wak said:
> 
> 
> 
> Excellent Guide John, but annoying about the construction quality looking at that chip as you say barely any solder on the pins not great quality and one could argue designed to fail. :?
> 
> The Repair looks like it will last forever.
> 
> 
> 
> Could also be the use of lead free solder that the eco hippies want to be used. All well and good except it's brittle and components don't last as long, thus ending up on landfill! Lead based for the win :lol:
Click to expand...

Maybe so just Johns first chip pic looks like solder free solder! :lol: It would have been nice to find a chip that didnt have legs as clean as a new one and they made some effort!


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## Trouble4

that is really good to know. thanks ....

I pay about $123.00 GBP for that part .......... Have never really understood why parts are so much more in UK ??

anyway great write up


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## warrenstuart

Excellent write up, as always [smiley=thumbsup.gif]

Warren.


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## JorgeTTCQ

Excellent, thank you very much [smiley=sunny.gif]


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## A3DFU

Thank you


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## John-H

Thanks for the translations Dani. 

I don't know if the G419 combined sensor suffers from the same fault and can be repaired just as easily. Definitely worth trying though.

Since they brought in RoSH compliance (lead free) they have improved the situation from the early soldering problems. I use it all the time at work and don't find it a problem now. A slightly higher temperature perhaps helps. It's not pure tin but contains other ingredients like copper, silver, bismuth, indium, zinc, antimony, and traces of other metals to make it work and they've probably improved the flux too. I don't worry so much about lead poisoning either [smiley=dizzy2.gif]


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## aidb

Something I would never be able to attempt myself, but an impressive "How to" as usual John.


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## A3DFU

aidb said:


> Something I would never be able to attempt myself, but an impressive "How to" as usual John.


Aiden,
are you ever going to crawl out of the woodwork again and join another cruise? :roll:

viewtopic.php?f=3&t=430602

Sorry for hijacking your thread John


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## John-H

That's Ok Dani. At least you won't have a warning light showing now on the cruise 

Interestingly "zeroing" the longitudinal sensor was confusing: Unlike the lateral sensor it doesn't zero to 0m/s but reports back 24m/s and a successful reset within perameters.

To confuse matters further the ESP warning light was still lit after zeroing the longitudinal sensor but doing a fault reading check revealed a steering angle error that hadn't been there when the longitudinal sensor was originally playing up. This was odd because the steering angle read back zero in the straight ahead position so appeared correct.

Still holding the steering wheel in the straight ahead position I zeroed the steering angle sensor anyway and was then relieved to see the error code would clear and the ESP light extinguish. A road test revealed no errors.


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## silkman

Sorry to resurrect an old thread but I need to clarify:

Longitudinal is G251
Lateral is G200
THESE NEED CALIBRATION WITH VAG-COM WHEN REPLACING.

Yaw is G202 (my problem) which is completely unrelated to the above. Does the yaw need calibration or not?


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## Skeee

Have a read of 
viewtopic.php?f=2&t=313096&start=15

and

viewtopic.php?f=2&t=153716&hilit


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## miknix

Hello,

Thank you for the excellent write up. I've managed to repair my sensor following this thread 
There is just on thing I would like to clarify. You said:



John-H said:


> *How to repair G200 (Roll - lateral) and G251 (Pitch - longitudinal) sensors*
> (...)
> *N.B. When using the above recalibration procedure G200 will "zero" to 0m/s but G251 will "zero" to 24m/s and report a successful reset within perameters if all is working.*
> (...)


When I put the repaired sensor back, I fired vagcomm and the sensor was reading 24.617 m/s. Does this mean I don't need to do a re-calibration, the value is just fine?

My repair thread: viewtopic.php?f=2&t=1323122


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## Antnkel

How easy was it to dig the parts out?
I've got one which I'm thinking of doing and what did you use to seal it?

Edit- just saw your link at the bottom :roll:


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## miknix

Antnkel said:


> How easy was it to dig the parts out?
> I've got one which I'm thinking of doing and what did you use to seal it?
> 
> Edit- just saw your link at the bottom :roll:


Digging the parts out from the assembly is pain the in ass, I started the disassembly of the module at 15h and finished assembly (including potting) at 19h!
I used black silicone, the one rated for making car and boat joints. It is pretty good stuff, I completely removed the dried joints around the rear lights and replaced them with this silicone (link: https://www.amazon.fr/Rubson-Mastic-Aut ... icone+noir)


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## Antnkel

Thanks, I'll have a look at that. I've got a spare faulty sensor so can take my time.


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## miknix

*Can please someone confirm whether the G251 sensor is supposed to be calibrated to 0 or 24 m/s??* I've been reading conflicting reports about this! On my car, using a repaired G251 sensor, after triggering basic settings for group 069, the measured value is around 0 when the car is parked.


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## John-H

From my write up G251 is set to 24m/s. This was a long time ago but I vaguely remember being surprised it wasn't zero but it was differently orientated. I may have swapped it with G200 under the steering column to double check or simply rotated it to the same orientation. Try that.


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## miknix

John-H said:


> From my write up G251 is set to 24m/s. This was a long time ago but I vaguely remember being surprised it wasn't zero but it was differently orientated. I may have swapped it with G200 under the steering column to double check or simply rotated it to the same orientation. Try that.


Yeah got it. I went checking the Bentley manual and there is something about it in the G251 "zeroing" section:



> NOTE: After successfully zeroing, the value indicated does not become 0.00 m/s2


It is not very clear what they meant by that, I'm assuming the value will be close to zero but not EXACTLY 0.00.


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## miknix

So today I went measuring the G251 accelerometer value just to make sure it was still working fine. To my surprise it was measuring 24m/s. I disassembled everything, popped the accelerometer out and removed all the gunk. This time I rechecked all the connections for continuity and measured the each component (mostly resistors) against their printed value. All was ok.

Then proceeded to hook the pcb to a 5V power supply, by knowing the IC pinout it was easy to find the pinout of the G251 connector:
1 - Vdd (+5V)
2 - GND
3 - Vout (accelerometer value)

Then I measured the 5V pin of the IC and it was spot on. Finally, I measured the voltage between Vout and GND - it was 2.5 V volts which matches the ZERO = Vdd / 2 mentioned in the datasheet. Then I found something, when tilting the accelerometer down, the value went from 2.5 V downwards. Tilting the accelerometer up the value went 2.5 V upwards.
Potted the thing again and put it back in the car. Using vagcomm to dump the measured values (Measure block 006 of ABS controller) I tried moving and tilting the accelerometer. Guess what? When tilting the accelerometer down, the value read by Vagcom is 24 m/s downwards. Tilting the accelerometer up the value is 0 m/s upwards. So basically, both 24 m/s and 0 m/s correspond to "zero" values - it is just 24 m/s is slightly tilted down while 0 is slightly tilted up! If that makes sense.


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## John-H

Hmmm ... not sure what's going on there. Just a thought but you don't need to tilt far to get to a good proportion of g. Obviously 90 degree tilt would be 1g one way and 90 degree the other way would be -1g. The interpreted readings don't make much sense to me as 1g = 9.8 m/s/s. However, disregarding the size of the numbers and integrating time, pulling 1g in acceleration terms is huge, so tilting by a small angle is normally very significant in terms of the ESP - e.g. a slight drift sideways is way less than 1g. Couple that with Vag-Com only sampling values at a slow rate (and I 've no idea if this particular reading is averaged) could it be that your tilt exceeded the slight offset expected or was not settled long enough?


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## DzieX

Hello,
Were you managed to find out if 24m/s acceleration is ok? I have same problem in my car which is Seat Toledo swapped to AWD with haldex and pump from Audi TT.

Here's my adjustment and reading:





I've sent G251 for repair, but with no effect. Then I replaced G200 with G251 but effect remains the same. I found out that when I'm accelerating readings are between 0 and 3 m/s, but when I slow down or ride with constant speed it shows 24.
There are no errors in VCDS.

I'm about to replace ESP pump, but if someone knows what is happening please let me know.

Thanks in advance.

-- edit
I have checked it on other pump with same effect.


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## DWL_Puavo

I just registered to thank you all for this topic. Great guide and pics! My 2000 TT 224q was registering intermittent G251 error and disengaging traction control, but not behaving abruptly. With these instructions I was able to fix the faulty sensor quite easily, and for me, it took a bit over two hours in total.

I removed glove box, then sensor was very easy to disconnect and remount. Removing all the gunk took a while, and I had to use pen-style desoldering pump to detatch the pins, desoldering wick wasn't enough. To remove PCB, I used sharp pointed O-ring tool / hook, as it was also easy to detatch the PCB from the sides with it. Chip was left into gunk, but it was easy enough to solder it back, with magnifying glass and a sharp tip.

I then used clear hot glue to create a kind of chip aquarium, it also worked out just fine.

Sensor reset didn't affect its original reading, and it was something different than 0 m/s^2, but for some reason, I didn't write it up. Everything works now as it should, no fault codes, no warning lights and no disconnected ESP while driving after two months now.


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## silkman

Congrats on the repair, you saved about 200euros 

I have written it elsewhere, why put bathroom sealants hot glue etc instead of the proper potting compound? 3M was the cheapest I could find, it was about 13eur for 90gr package. Easy to put, just mix it and open a SMALL HOLE in the pack to pour.

3M part 397055010, comes in 90, 200 and bigger sizes, same part number


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## John-H

Congrats on the repair - always best to have a go. Often these things have such a simple failure that can be fixed for pence. Dry joints are very common.


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## fire88

Thank you so much John 

Another happy TT owner with those shitty sensors. 

Sent from my GM1900 using Tapatalk


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## magwych

With it being spring and nearly Easter, I don't feel too bad about resurrecting this thread ...
The ESP light on our TT had been playing up, on and off, since we got the car. 
It was worse in the warmer months, sometimes it would come on before the car had even moved. Over winter it has been persistently cold here, and the ESP had behaved impeccably. Now it is starting to warm, daytime temperatures sometimes get above 10C, and it was playing up again.
Following this thread, I decided to tackle my G200 sensor, VCDS Lite was picking up the errors as "intermittent power G200".
Getting the sensor out was surprisingly easy, once the dashboard end panel was loosened entirely. Cutting the potting compound out took a while, and was particularly fiddly around the plastic mounting posts and the terminal pins.
I used a hook shaped scraper to shred the potting compound below the chip, which allowed me to pull the circuit board with the chip still attached. In these photos you can just see that one or 2 legs are not attached to the board.


















Don't worry folks, I have an anti static wrist strap on ;-)

I removed the chip, tinned its connection ponts on the board, then soldered it back on. 

I used a black silicon mastic to repot the boatd, after somdering it back in. Confession time : I damaged the circuit track around on of the pins in my enthusiasm to clean off the old compound. I used a short length of tinned wire in a heat shrink wrap to bridge from pin to a convenient point on the board.

Reassembly was the reverse of dissassembly. The hardest part was getting the clip back on to the bracket in exactly the right place. Working blind, on the underside of the dash with the steering wheel in the way did not help. 

I have just got back from a quick blast around the neighbourhood. No ESP light on permanently. Pushing a bit hard on loose surfaces I was able to get the ESP to kick in, light flashing as it ought to.

I am well chuffed, now enjoying a celebratory pastis


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## Hoggy

Hi, Congratulations & well done, cost me £164 for the sensor.
Hoggy.


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## fire88

Bought a second hand from UK for 80$, before I eventually fixed mine. 

Now I have spare part. 

Sent from my IN2020 using Tapatalk


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