Noise/sensation question: ABS or 4Matic?
 

Gretel - our 91 300 TE 4Matic - has us pondering over a new trick.

Rolling up to a slow stop, we sometimes get a slight feeling through the brake pedal that almost feels like ABS engaging - on a small scale. ABS engagement, if it's happening, shouldn't be surface related (one, this only happens at slow rolls - speeds like 2-3 mph. Two, it doesn't matter whether the road surface is clean & dry or sandy or wet.)

So - we're wondering if what we're feeling is the 4Matic kicking in.

Figure the next step (one for tomorrow morning when the sun is up and the 151 is flushed :P) is to flip the 4Matic test lever to the off position and see if I can reproduce the feeling.

Any ideas anybody?

You could be experiencing the abs/4 matic because if the system senses a slip in the wheel it will apply and do what you are describing even its sunny. Conditions doesnt matter in this case. if senses a wheel slip for whatever reason the abs computer will send a signal to apply the brakes and engage abs.

What is the likelihood of getting a false slip reading off of a sensor? If this is the case, what are the troubleshooting steps for finding (and correcting) the root cause?

Thanks!

to clarify 4 matic is mercedes 4 wheel drive and is a completely different system from the ABS. The 2 work together so I hope I didnt confuse you. A bad abs sensor will cause this problem. To see if your sensor is bad measure the voltage at the sensor or get the abs codes stored in the computer. the code will tell you what one is faulty. Also you could pay close attention to what wheel applies when it happens.

Understood re: ABS vs. 4Matic.

If you happen to know the correct voltages for the sensors, or can point me toward schematics with this info, that would be greatly appreciated.

I'm assuming the sensors are going to be located somewhere near each corner - on/near axles/CV joints up front I presume? (early unscientific 'testing' suggests that left front is the source).

Also - additional info or potential red herrings - simulated panic stops last night (dry pavement, standing on the pedal from 60mph down to 20mph) did occasionally result in brief (maybe 1.5 - 2 second) lock up of one wheel. Seemed to be left front. New General Altimax tires (less than 500 miles), dry clean pavement, straight road, 80*F air temp, probably +10 at the street, tires well warmed prior to 'test' was executed. Repeated half dozen times, got quick squeal twice.

First Check:
Pull the front sensors and clean them..they get full of rust filings and don't give a signal at low rpm..this get mis-interpreted by ABS module as a skidding wheel and engages ABS system...very common.
If they are clean, then do an ohms test on each..the plugs are up on the inner fender well, each side..follow the cable up to the connectors.........

Excellent info!

If that doesn't cure things, next I'll try pulling codes - found this excellent site http://pages.prodigy.net/jforgione/MB_DM.html doing a search on Read ABS Codes here on mercedesshop.

And the darling wife says to say thanks to each of you for your quick replies - and that she will keep her "nah nah nah I was right!" dance at a reasonably low level of intensity until such time that we confirm your suspicions :P

noise/sensation
 

Before digging into a complcated and usually reliable system such as ABS, I would like to offer the following.

The symptoms you describe are classic for warped front brake rotors. I had a similar problem on another of my vehicles (admittedly a non-Benz). One of the clues is that the problem develops over time. Heat generated during heavy braking is usually the culprit.

<The symptoms you describe are classic for warped front brake rotors.>

Classis ABS activation..
He said when he is coming to a rolling stop, he feels ABS activation..Classic ABS, for sure. A sensor is dropping the signal.
Rotors are pedal pulse , not ABS activation. And more noticed at higher RPMs, not low.

Update......

Found the sensors, but can't yet get the bloody things off (salt sucks!).

The pair of allen head cap screws holding each sensor in place aren't the star type, and they seem to be right about half way between a 6mm and 8mm size - and of course, I have no 7mm.

Odd thing is, I don't think I've ever run across an odd size metric allen head before. Am I letting rust particles cloud my size assessment, or are these actually 7mm allen heads?

From the just in case I'm totally missing the boat desk: It appears that these two cap screws must come off to remove the sensor. If that is incorrect, please - set me straight!

What is odd about 7mm ??
Allen even come in half sizes [ 4/5 5.5/ etc....]

Odd as in 'not an even number.' Just my limited Benz wrenching showing through I guess (have torn multiple Miata's down to the bare bones and built 'em back up again, and I can assure you there is not a single allen head cap screw anywhere in that play).

So I guess it's off to the FLAP place to try and procure a 7mm allen driver. Will (carefully to keep the PB Blaster off the brakes!) soak the little buggers tonight after we get home, and give it a run tomorrow.

Thanks again folks - your knowledge and willingness to help is greatly appreciated.

Maybe they are 8 and are crapped up.
A good way to clear them out is with a pick ..you can scrape into each hex corner that way. I will check on a car here ...

No 4matic to check..but a couple of standard 124 Benz and they take 6mm...

Mercedes are much harder than a miata's. They make you much work more than other car manufacturers.

Well, they definitely aren't 6's (spins) and they aren't 7's (won't go in even after clearing the slot of rust). I don't have a 6.5, and neither do the two FLAPs or Sears.

So they "became" 1/4" hex with a little friendly persuasion. Figured the heads were rusted up enough I wasn't going to re-use the cap head screws anyway.....

Sure enough, the left front sensor was full of filings and crud as suggested by Arthur. Right side was only mildly dirty.

And of course, neither FLAP store had the right bolts for replacements, so I'll be trying the not so local Napa tomorrow morning. Worst case, it's off to the nearest Benz dealer (~30 miles away).

If you were able to pound a 1/4" in there , then they are 6.5mm b/c that would be .255"...and a 1/4 is .250"..

If the 1/4 works , reuse them after cleaning just to see if that solves the signal dropping.
You also want to blast some brake cleaner into the sensor hole and spin the wheel to clean the reluctor segments..and a good blast of compressed air.

Here is a good read on how wheel sensors basically operate and testing them. It will give you some insight to the actual electrical working/theory and design. Te atricle was a diagnosis one, but the lead-up info is a good Teach.

http://www.picoauto.com/tutorials/diagnosing-abs.html

Thanks for the additional info. Reuse of the existing cap screws ain't gonna happen - while I could probably get them back in tight enough to do some test drives, whether the crud all over the front sensor is the root cause or not, I need to replace the screws. Don't need the car to be done today (or this week, for that matter) so I'll go ahead and get the right cap screws first and proceed from there.

Variable-reluctance sensors I understand - theoretically and in practice (one of my three Miata's uses the same technology on it's crank position sensor).

Thanks again Arthur!

Yes , they are all the same "Hall Effect " principle...simple as that.
And knowing the problems that Hall Effect sensors have with low amplitude output at low rpm's, one can see where they have to be perfect , b/c if they are not, they show up as fail @ low rpm...which is what we have with your car..acting up as you come to a slow stop..[ low speed wheel rotation], resulting in the ABS module reading this "no sensor signal " as a locked/skidding wheel......

Got new fasteners (not from the dealer - nobody has 'em in stock!). Cleaned up the reluctor teeth as best I could. Right front looks pretty darn clean, the left has some rust on the teeth.

Still getting the same symptom - ABS engaging at low speed.

Help me understand something - am I fooling myself into assuming that since the ABS feels like it is pulsing the front wheels only (specifically the left front), that I have a front WSS issue? Is it possible that I have a rear wheel speed sensor issue? I haven't opened those up for inspection yet.....

I read through the article you linked above Arthur, and see that the root cause in that situation was misalignment of the sensor due to damage/corrosion. As best I can tell, the sensors are mating as designed. There is some corrosion on the mounting surface on the left wheel, but the sensor mounting bracket sure looks fully flush and parallel.

Both front sensors measure 19.98 kΩ at their respective connectors near the firewall. The article mentions 1.734 kΩ - not sure if that is what I should be expecting on my WSS's or not. Order of magnitude difference, but both reading the same, leads me to assume they're different sensors than those in the article - can you confirm or correct this? (i.e. what should I be seeing?).

Much obliged!

Once I get this settled out, the CV boots get replaced....... always another project (or ten).

Once you get to that point, you really have to have a Scope...that is the omly way to see what the ABS module is reading...
You can ohm the rears and look for bad wiring at front ones by flexing the cable while watching the ohms values for change, etc...but once you are to this point , a scope is the tell.
I don't even do primary ohms/volt test on WSS...I go right to a scope wave pattern.
You may also want to test the ground side of the sensor cable to a good ground w/ohm test to be sure of a good ground at mounting ..should be trace/none..

That second section of the article was an oddity, so I would not search in that same direction...I believe you have a weak sensor and a dirty/bad reluctor..and that is why you need a scope if all other continuity an ohms test look OK.
If the ohms and wires look OK, then the sesnors SHOULD work as deisned, but you can see that there are distance spacings and magnetic properties that come into play and thew ECU will pick them up, an ohm meter wont...and a Good Scope has no problem , as you can see by the wave forms he displayed. [ and the reason why I posted the article..I thought he did a good job and is one of the better ABS ones]
There is one thing I did not mention, but is a possible with some sensitive systems..the tire sizing/pressure must be uniform or a sensor can mis-interpret wheel speed imbalance due to rolling circumference differential..this is actually quite common on ASR system and will actually bring on codes.....doubt that to be the problem, but a consideration

Just read thru the typos b/c I get tired of having to constantly edit...I can't type to save myself and I hit send before proof reading my post.. I see them later some of them are BAD ..............:)

<<Both front sensors measure 19.98 kΩ at their respective connectors near the firewall. >>

Is that a decimal typo ??
Spec for front on that chassis is .85-2.3K
Rear is .6-1.6K

Ah - not a typo, but was an error on my part. Went back out and double checked my tracing of the cable to the connector - my 19.98 kΩ readings were on the wrong side of the connector :o

Actual readings are within the range you gave, but over a spread:

RF = 1.023 kΩ
LF = 1.611 kΩ

Is there any chance this amount of difference between the two could be a factor?

As of tonight, getting the left front axle out has moved up the priority list - the inner CV boot has progressed from "gee that looks fatigued" to "has an actual split" so Gretel is going to stay as parked as possible until I can get the boot replaced. At that point, I'll do a proper clean up on the reluctor teeth.

I don't think so....
....in spec.

Update: got the boots!

Quick plug for Phil at Fastlane - this guy rocks! Called him up since I was confused by the photo in his catalog.

Wanted to make sure I wasn't ordering more than I needed - text read that I'd need an inner kit and an outer kit, but the photo showed two boots in the outer axle kit. He checked, and concluded that the outer kit contained everything. Placed my order, then got a follow up email - seems on further checking, I did in fact need both kits, so Phil was going to ship both - at no extra charge. I would have been perfectly happy to hear "I was wrong, sorry, you need to order the inner kit separately" but Phil wouldn't have it. "I said you only needed the one, so I'm not gonna charge you more" was the gist of his reply. :2thumbsup

Anyway - now I'm ready to pull the axle to replace the boots, and (back to this thread :P) clean up the WSS related bits.

Any pointers - link to a step by step guide, with photos, per chance?

Another update
 

Got time this morning to replace the CV boots on the left front.

Found the teeth on the axle that the WSS reads to be truly crapped out with rust - something like 30% of them had reduced or non-existing gaps between the teeth (rust growth). Seemed kinda odd, since the other surfaces in the vicinity weren't bad at all.

Judicious application of a wire wheel cleaned 'em up just fine.

Now, the original problem (ABS kicking in on slow speed stops - down at 2-3 mph) is happening on damn near every stop instead of some to most.

My guess - since I believe the ABS is looking at wheel speed differentials - is that I just upset the balance between two almost equally crapped up set of teeth. So, tomorrow's mission will be to pull the right front axle and clean those teeth up.

Will also trace back on the rear WSS's and check the resistance on those.

Any other thoughts, observations, suggestions appreciated.

Turn the steering from lock to lock a couple of times.

Did that this morning. Cleared up the half of yesterday's observations (the half that I forgot to mention): yesterday, every time the ABS would engage on a slow stop, I'd get the 4matic light to come on as I pulled away.

Today, after going lock to lock with the steering wheel 4 or 5 times, the ABS still engages on every stop, but the 4matic is not engaging on take off.

Any other suggestions Arthur, others?

It's not looking like I'm going to pull the right front today to clean that side up - is this even worth doing, or am I barking up the wrong tree?

Also - any hints as to where I would find the connectors for the rear WSS's?

Thanks again!

heres what i did trying to track down an identical problem.connect a DVM to each wheel sensor at the coaxial connectors in the engine compartment.attach meter to windshield with duct tape.drive car at slooow speed and observe voltage readings.the sensor with the lower reading is the problem wheel.rear sensor is either good or bad but you can measure it too by finding the connector under the rear seat.the air gap between the sensor and axle teeth is very critical.but there is no adjustment.possibly the teeth are worn down:)

Did you disconnect the sensor, and just read voltages (resistance maybe?) from the sensor side of the connector, or did you figure out a way to measure voltages with the sensor connectors still connected?

It is very difficult to get a concise diagnosis from wheel speed sensor/reluctors output without a scope to examine the ac sine wave pattern. You can ohm them and you can take DMM output voltages , but you really want to see what the ABS control module sees ..and that is the sinewave.
...which is why I posted the article......
It take one little glitch to activate ABS , specially at low rpm [ output]

you can see the rms a/c voltage output of the sensors this way.crude but effective.my right sensor had 1/10 the a/c output of the left despite a new sensor on that wheel.thats how i tracked it down.your dvm probes wi:)ll fit into the female side of the coaxial connector.drive at sloww speed below where the speedometer will register

Have you ruled out 4matic?
 

My 91 4matic sedan has a 4matic test lever under the hood used to disable the system. On your car, I believe that it will also disable the leveling system, but that shouldn't be a problem for a short period to rule out a 4matic issue.

I would disable the 4matic and see if the symptoms are the same.

Grrrrr!
 

Getting really frustrated now. Pulled the right front this morning, cleaned up the teeth that the WSS reads, no change.

To recap:

1. 1991 300TE 4matic, 147k miles
2. Getting ABS engagement on every stop when speed falls below ~1-2 mph
3. Both front WSS resistance readings are within spec - checked again today: 1.598kΩ (left) and 1.020kΩ (right)
4. Both left and right front teeth were crapped up with rust. Both cleaned. No change.
5. ASR light (mistakenly called 4matic light by me yesterday) comes on sometimes when pulling away after ABS has engaged on previous slow roll stop (definitely NOT due to wheel slip)
6. If I do a panic stop from 20/30/40/50/60 mph, ABS functions normally
7. If I hang one side off in the gravel and stomp the go peddle from a dead stop, ASR functions normally
8. Flipping the 4matic into test mode (lever on right front fender wall) makes no difference to any of the above

Questions:

1. Where can I find the connectors for the rear WSS's (would like to confirm 'under the back seat' is correct for my wagon before I start tearing up carpet)?
2. Lacking a scope to get more meaningful readings off the front WSS's, what are my options for further troubleshooting?
3. Does it make sense to pull the rear wheels and do the same 'clean out the rust' routine on the teeth there?

W/O a scope , you can try a DMM as Cole suggest..
I would jack each front wheel and take a V reading at 60 rpm. [ 1 rpm/sec]
This can be done with a little practice. You get the tire going smooth by putting a finger on the side wall and spin the tire with your whole arm and count in seconds...You can actually get it pretty close if you do 5-10 sec rotations.
Then compare the V of each side. [ @ approx same rpm]
The problem with hall effect sensors is the amplitude [ voltage] increases with rpm , so slow rpms show the first drop to the ECU [ which is why you have activation coming to a slow stop.]
So, that indicates either a glitch [ only scope will show that]..or a V drop from a sensor [ caused by sensor /reluctor/spacing/etc ..you know the drill.].....
My concern would be the % of ohm differential reading you have between the two fronts..they are both spec, but I would suspect a difference in ohm values that large to possibly show up as a lower V on the lower R side at low RPM..[ in other words, that one would likely drop V to zero sooner than the other ]...just a possible
Scope is the tool, no matter what other test are done..but when you don't have one , you punt.

Ramonjim.your front sensor ohm readings are good.nothing to worry about there.i suspect the teeth on one or both of the front axle tone rings are worn down a little bit from corrosion over time.the air gap between the teeth and the sensor is the critical dimension here.some ac voltages would be handy now to further troubleshoot.dont worry about the rear sensor too much.you can get the ohm reading at the plug which is under the right rear seat under the carpet.carefully lift the carpet the edge nearest the door.you will find it right under there.the rear sensor mounts into the rear differential and as such is protected from rust.the sensor is easy to remove for inspection and cleaning.ive tried the scope method on the front wheels but found the ac sine wave difficult to interpret so im recommending you try hooking the dvm to the connectors in the engine compartment and driving the vehicle with the dvm taped to your windscreen.you will see the ac voltage fluctuate fairly rapidly.have an assistant watch the meter and keep your speed below where the speedometer begins to move.:)

<ive tried the scope method on the front wheels but found the ac sine wave difficult to interpret so im recommending you try hooking the dvm>

There is NO comparison to a sine wave and a DMM reading when diagnosing hall sensors.
I am also recommending the DMM , but only b/c he has no scope..certainly not b/c a DMM is the better diagnostics tool for hall sensors...for sure.

First off, thanks again to all who are helping out.

Second - Michael, your note about the mounting of the rear WSS opens another set of questions in my mind (and your thinking that I could be facing a front axle replacement ($1156 each!) frightens me - two of those would be damn close to what I paid for the car!).

Gretel has a noisy rear end (noise when loaded either from accel or decel, quiet when unloaded). My guess is that the rear WSS is NOT looking inside the diff - and therefore the noisy rear end shouldn't be a factor here. Can anybody confirm or correct that guess please?

Also - I'll throw a meter on in either or both Michael's and Arthur's suggested methods. Assuming I find one corner different enough to be deemed the trouble spot - how do I positively determine if I need to replace the WSS vs. the axle?

If you find the problem w/DMM , then you are good...but before I spent any $$$ for parts, I would go to someone to get a scope pattern for a proper diagnosis.
A scope pattern with a flattened sine wave peak on the amplitude of the pattern would point to airgap excess of reluctor. Just one of the many possibles that a sine wave shows and a DMM won't. BC this is such a low rpm wheel speed complaint, I would want to look at EVERY single tooths sine
wave, b/c that wave will show what is the cause of ABS activation when the complaint is ABS when coming to a very slow stop.....even loose wheel bearings will cause that complaint.

i do concur with arthur on possible wheel bearing issue being a root cause and would recommend checking all the easy stuff before axle replacement.to be honest i havent resolved my own problem with this yet but i have nailed down to the right front wheel.the axles are mucho$$$.all teeth appear to be in good shape but they have been coated with rust before cleaning.im thinking now about possible measurement of the air gap with a feeler gauge at the known good wheel and comparison with the bad.i can see that a loose wheel bearing could give several thousands of an inch play and depending upon the air gap tolerance could be a factor.the airgap can be accessed at the rear of the hub so you dont need to remove the sensor.its also easier to blow compressed air in that way for periodic cleaning.:)

Well, crap.

Checked both front WSS AC voltage readings as described by Arthur (probe WSS connector, female side, spin wheel by hand at ~ 60 rpm).

Left: ~ 0.028 to 0.031 VAC

Right: ~ 0.250 to 0.290 VAC

Pulled the left front sensor, and checked the mating surfaces (sensor and hub). Sensor was clean, but the hub had a couple small mountains (eyeballing it, I'd guess maybe 0.050 - 0.060" high) of rust within the mounting area. Eureka, me thinks! Cleaned those up (small grinder) and replaced the WSS.

No change in the left front reading. Crap.

So:

Left WSS reads higher static resistance (1.598kΩ) and lower low speed voltage (0.028 to 0.031 VAC).

Right WSS reads lower static resistance (1.020kΩ) and higher low speed voltage (0.250 to 0.290 VAC).

Options for determining which component is the culprit?

1. Chuck the DIY mode and take it to a Benz dealer. What are my chances of getting a dealer who will actually hook up a scope and DETERMINE which part is the fault, rather than just have me pay to replace parts until it is resolved?
2. Replace the wheel bearings. I have no records indicating when they were last done, so I could maybe convince myself it 'needs' done now.
3. Actually CHECK the wheel bearings. How do I determine their health?
4. Temporarily replace the axle with a known good unit. Anybody got one I could borrow?
5. Other ideas?

My only other request (for right now :D): where do I fax a tall cold one in appreciation of your help?

Stick the depth gauge rule from a vernier in both sides w/sensor removed and see how the reluctors measure from the top of the sensor mount hole. Compare..side/side.


<<Left WSS reads higher static resistance (1.598kΩ) and lower low speed voltage (0.028 to 0.031 VAC).
>>

Flex that cable around where it enters the sensor while you have the ohm meter hooked up and look for that value to drop/change ..you could have a poor connection in the harness , causing higher R / lower V........
That would fit the slow stop complaint while no other ABS problems b/c as soon as WSS sees a higher rpm [ even 3-4 mph], the amplitude of the sensor [ V] is high enough and verified for the ABS module to be satisfied..

How much V can you get out of that side if you hand spin that wheel as fast as possible by hand?.... and does it drop V before stopping earlier than the other side ?

No dramatic difference in spacing side to side: a 20 teeth from around the full diameter on each side, all fell within +/- .004 of 1.025" from the mounting surface to the top of the tooth.

No obvious open/short in the cable - wiggling produced no more than a .005kΩ change.

Max voltage left: 0.051 VAC
Max voltage right: 0.345 VAC

Left dropped to meter reading of nominal zero (0.002 VAC) pretty much right as the as the wheel stopped spinning.

Right didn't drop to a meter reading of nominal zero until just after the wheel stopped spinning - didn't put a stop watch to it, maybe a full second, maybe two - but markedly different that the left.

Does this mean funky left WSS?

<Does this mean funky left WSS?>>



That would be my guess.
Reminding all that w/o a scope reading , that is a logical guess only...

Might want to try that measure with tire suspension loaded [ some blocks under tire so you can get to hole again.
How do the working height of the 2 sensors compare ??? [ does the end of the sensor look worn down from debries/reluctor rust]

Are those MAX readings when you increased the hand spin tire speed??

Yes - spinning the wheels as fast as I could by hand:

Max voltage left: 0.051 VAC
Max voltage right: 0.345 VAC

Well, looks like a bad/weak sensor ...
I hate to do a diagnosis w/o using the proper equipment , but in your case it would be a pretty fair and logical determination.
There are many articles that claim the sensors can loose the flux propertires by getting jarred or even by the front end parts getting rapped with a hammer when doing repair work on tie rods/etc...so, no shorts, no bad connection, reluctors check, ohms spec , etc could equate to a weak sensor.
Just b/c a sensor ohms out spec does not mean it generates the proper/ required signal... [ that's where we go back to a scope..we are not interested in the coils ohmic value, we are interested in the sine wave the sensor/reluctor generates...an ohm value just says it is supposed to put out a signal..I want to SEE that signal when I diagnose.]
You are seeing the V output [ or rather , the weak V output], so bad/weak sensor possible looks better than anything else at this point.

I'll be getting a sensor on order from Phil later today.

Arthur, please accept my sincere thanks - your willingness to educate me through this process has been wonderful.

I understand (and appreciate) your hesitancy to make a firm call without the complete diagnosis a scope could provide - let alone make a call from across the interweb without ever having laid eyes on the car!

By answering my questions, and building on the info that I could provide in response, you've not only pointed me to the most likely solution, but you've a) reminded me of the value of truly understanding what is going on in a system, and b) got me comfortable inside a system I'd not previously poked about in.

:thumbup: and thanks. I owe you a beer.

Once you understand how cars work and how each manufacturer does things they arent so bad.

VeryGood..
There was a time when a mechanic that was savy could diagnose a common automotive circuit with a test lamp and a couple of jumper wires ...then the DMM came along , giving the user an expanded view into these electric circuits ... cool, ....but now we have gone from Basic Electric circuits to High Tech Electronics ..so, a Scope is simply the next generation DIYer tool required in the diagnostics process.
You can buy a good DSO scope on Eaby for less than the cost of a WSS..and once you get one it will open your world of Electronics understandings far beyond than when the DMM was " THE TOOL" to own.
[ Many of us Vet guys were brought up on Analog Meters and have a preference to them even today... I Love My Simpson 260 to this day...:)]

So,....... as Auto-Tech evolves with Frequency and Pulsed Code formats , along with digitized signals,CAN etc., a scope is going to be mandatory ..........almost that way already.
You can find SUN LS-2000 DSO scopes for a couple hundred ..very good tool and user friendly..keep your eyes out for one.
Here is one that also had the Ignition Probe included..$225..[ about 1/10th the original cost..not bad.}

http://cgi.ebay.com/ebaymotors/LS2000-LAB-SUN-SCOPE-from-SNAP-ON-TOOLS-used_W0QQcmdZViewItemQQcategoryZ43989QQihZ003QQitemZ130244765814QQrdZ1QQsspagenameZWDVW
...and That Pico site is a great read for anyone considering a scope.

good to see your making some progress on this problem.most folks are not as patient.i was going to say if your seeing .004 variance in the tooth height that could be significant.im urging caution with regards to sensor purchases.i now have 2 good spares and the same problem:)