Can any one help with this issue

Shahzad

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Recently got MOT passed, service done from
Mercedes few days ago suddenly abs and esp lights turn on, went to local mechanic he diagnosed with ABS front left sensor. Went to another mechanic for second opinion he advised me to replace brake pads as it was 70% wear and also he suggested me to change brake pads sensor replaced both of them. Getting new code after driving 5-10 mins he diagnosed with no codes all clear, so After driving for another 30-45 min both lights came back. Should I go for abs sensor replacement? Mechanic is saying abs sensor is fine it might be something else needs to be diagnosed
 

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ManofKent

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My abs sensor went on the rear offside wheel. Apart from the two warning lights you mention it wouldn't go into cruise control until fixed. Mine was the ABS RIng, not the (easier) pulse sensor, a bit more expensive but not too bad.

John
 

CClassPokemon

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I also have a W204 and am currently having the same issue as you. The manual says that low battery voltage can cause this issue - it seems cheap and easy enough for a layman like me to check this myself, so I am doing that first before taking it to a workshop.

Therefore, I recently gave mine a full charge and recond with a CTEK MXS 5.0 to see if it resolves the low voltage issue. When I checked the voltage beforehand, it was 12.1 (not good). Immediately after disconnecting the charger, it was at 12.7 (good). But then I checked it the other day and it's sitting at 12.2 with the engine off (not sure if this is good or bad to be honest - probably a bit on the low side).

Next I will check the voltage with the engine running to see if it increases to 14 volts or so (if it does, I assume that means the alternator is able to charge the battery ok, but the battery is not holding the charge - in which case it looks like a new battery is needed).

To cut a long story short, I'm just trying to work out if I need a new battery or not as the current battery is getting on 9 years old. So if I need a new battery, I will do that first to see if it resolves the ESP / ABS warning lights. And if it doesn't, I will take it to a workshop.
 

SMS

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I would have gone with the first garage, very common fault and second garage just had you fro brake pads without diagnosing the fault. Brake wear will not cause an abs fault.
Why didn’t you trust the first diagnosis? as the second one has replaced parts that have nothing to do with original fault.
 
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Shahzad

Shahzad

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I would have gone with the first garage, very common fault and second garage just had you fro brake pads without diagnosing the fault. Brake wear will not cause an abs fault.
Why didn’t you trust the first diagnosis? as the second one has replaced parts that have nothing to do with original fault.
He was considering Mercedes report on last service where is says brake pads are 70 percent wear so he suggested to change brake pads and brake pad sensor it would work, as per his personal experience and diagnosed
 

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Shahzad

Shahzad

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My abs sensor went on the rear offside wheel. Apart from the two warning lights you mention it wouldn't go into cruise control until fixed. Mine was the ABS RIng, not the (easier) pulse sensor, a bit more expensive but not too bad.

John
I guess it’s for traction it would link with abs system, even eco button is not working due to electrical fault it has some link
 
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Shahzad

Shahzad

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I also have a W204 and am currently having the same issue as you. The manual says that low battery voltage can cause this issue - it seems cheap and easy enough for a layman like me to check this myself, so I am doing that first before taking it to a workshop.

Therefore, I recently gave mine a full charge and recond with a CTEK MXS 5.0 to see if it resolves the low voltage issue. When I checked the voltage beforehand, it was 12.1 (not good). Immediately after disconnecting the charger, it was at 12.7 (good). But then I checked it the other day and it's sitting at 12.2 with the engine off (not sure if this is good or bad to be honest - probably a bit on the low side).

Next I will check the voltage with the engine running to see if it increases to 14 volts or so (if it does, I assume that means the alternator is able to charge the battery ok, but the battery is not holding the charge - in which case it looks like a new battery is needed).

To cut a long story short, I'm just trying to work out if I need a new battery or not as the current battery is getting on 9 years old. So if I need a new battery, I will do that first to see if it resolves the ESP / ABS warning lights. And if it doesn't, I will take it to a workshop.
On Monday I will get proper check of battery and abs sensor if something works will share it you. I was reading on some forum it could be a battery, sensor or brake switch issue. Even I booked appointment with Mercedes if local workshop can’t fixed it will consider to use their services to get rid of this issue. They are charging £120 per hour for diagnostic than parts and labour seems around another £500-800
 

MilesWFB

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Check to see if your alignment is off, mine had the same symptoms due to really bad alignment.
 
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Shahzad

Shahzad

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Check to see if your alignment is off, mine had the same symptoms due to really bad alignment.
But last month I had a service from Mercedes I hope they checked everything I do have a report from them. Sharing with you
 
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Shahzad

Shahzad

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But last month I had a service from Mercedes I hope they checked everything I do have a report from them. Sharing with you
 

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MilesWFB

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Thanks for that, Not sure if they check for alignment, A pothole can knock it out of place and this can trigger the sensitive sensors related to this. The easy way to check yourself is if you are driving in a straight line the steering wheel should be the dead centre if it is quite off (left/right) then it might have the chance of being the cause of your problems. It's an easy way just to check, it's only an idea though as this was my issue.
 
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Shahzad

Shahzad

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Thanks for that, Not sure if they check for alignment, A pothole can knock it out of place and this can trigger the sensitive sensors related to this. The easy way to check yourself is if you are driving in a straight line the steering wheel should be the dead centre if it is quite off (left/right) then it might have the chance of being the cause of your problems. It's an easy way just to check, it's only an idea though as this was my issue.
Thanks will try this in the morning
 

SMS

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He was considering Mercedes report on last service where is says brake pads are 70 percent wear so he suggested to change brake pads and brake pad sensor it would work, as per his personal experience and diagnosed
Thanks, although 75% of the cars we see that are told they require brakes after a “free” Mercedes inspection don’t.
 

Will

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Worn brake pads will not give an ABS fault, or indeed a fault code for a wheel speed sensor.

Second mechanic doesn’t seem to understand the fault. Your first diagnosis sounds more plausible to me.
 

Tuercas viejas

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Interesting series of posts in this thread.
First a broad statement , brake pad wear will NOT trigger an ABS ESP fault.
Brake imbalance when something is worn like a wheel bearing may sometimes flag the system if conditions are right, including steering wheel/column is out of adjustment by more than 5 degrees variation from center to center steering lock, i.e full L/H to R/H . That is simply put because its part of the stability control system interface.

Now this is NOT rocket science rather its the use of a professional style scan tool incorporated with oscilloscope features.
Obviously a code or two gives the clue, but switching to wave form program PID on the scan tool will allow the operator to "see' each four corner wave forms as you roll the car forward and back. Sometimes you simply drive the car up to about 30mpg with an assistant observing the wave form activity which MUST be uniform. You can't go much faster than that since these systems cut the scan tool communication for safety reasons.

If you have to as a tech be closely looking at glitches to solve a problem at speed, (say going over a road bump causing loss of communication) then a full 4 or 6 channel oscilloscope directly connected to each sensor circuit is what's needed. Now Picoscope automotive series tool at about $6500 , even has a wave form library built into it, so it can be used as a reference point for mechanic dummies who are inclined to want to shot gun the repair by guessing.
In my shop the wave form study diag' accounts for about 1 in 50 repairs involving wheel speed related issues.

The other of course is just BASIC electrical related.
Wiring bad communication due to high resistances , low supply voltages including a loss of the high speed Can-Bus circuitry.
As this is a Euro based BIG three brand (car/vehicle ) I swear the harnesses etc were made/designed by Chef Boyardee .

Now with diagnosis, brand knowledge is essential, and "some" is platform familiarity from brand to brand being "really essential" & of course knowing what you are dealing with, but ostensibly (MB in this case ) uses two distinct systems depending upon year /type /vehicle /model etc .
Here's some Sunday afternoon reading matter on the subject:-

Wheel Speed Sensors – Active and Passive

As a further comment why do shops in the UK not give the customer a print out of the scan tool results ,since many of you are paying for the diag scan tool service which costs money?.
In today's connected world its just a touch of a button to print out results, send to R/O archives. even aim the bloody scan tool at the problem area, and take a photie from the customer to see.

The other was a chuckle into my morning cup of PG Tips observing the uploaded MB dealer multi choice inspection sheet. OK by itself, but who is the team leader I ask????
Who do they think they are???
In the Royal Air Force doing the Battle of Britain thing with customer's car ???
Or is it one of those besuited individuals getting a wage for swanning about with paper in his hand !. OH me Gawd!!

Reading these posts, its a formula for a bad or inconsistent repair, & a comeback with & angry customer to go with it!
Where's team leader I ask FFS ??--He's been fired and he's left on the horse he rode in on! :eek: :wallbash: :D
Tuercas Viejas.










e

,


.
 
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SMS

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Never seen pad wear trip an abs sensor fault in 25 years of working on mercs and yes we do give out the Star test print out when it’s paid for.
 

MrGreedy

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On some comments and questions in this thread, and not in relation to one specific point. I'm also not intending to diagnose as I don't have any in-depth understanding. I'm just chipping this in as it might be useful knowledge.

After charging, your battery should be holding 12.7 volts (maybe a little more if it's an AGM battery) for extended periods, like days or weeks.
If it's not reaching this voltage 24 hours after charging (because it takes a while to stabilise after a charge), either the battery is duff, or you have some serious parasitic drain coming from somewhere.
At 9 years old, battery failing would be likely, but of course age isn't a 100% indicator that you don't have parasitic current drain.

Some discussion on voltage:

Someone has already suggested that low battery is mentioned in the handbook around this issue.

ECO stop/start not working is also a classic symptom of low battery.


One final point:
If you have an AGM (Acid Glass Mat) battery, you must not use the recondition function on the chargers. That is designed for normal flooded/wet lead acid batteries. It works by attempting to remove sulphate deposits off the lead in the battery by electrochemically inducing hydrogen gas generation. These gas bubbles are intended to help dislodge the sulphates.
In an AGM battery, it is as it sounds, a mat of materials, and is therefore not suited to the reconditioning phase.
Plus, the car electronics shouldn't be exposed to the higher voltage used during reconditioning because it can damage them. You would disconnect the wet lead acid battery from the car before performing this reconditioning charge.
 

Will

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Interesting series of posts in this thread.
First a broad statement , brake pad wear will NOT trigger an ABS ESP fault.
Brake imbalance when something is worn like a wheel bearing may sometimes flag the system if conditions are right, including steering wheel/column is out of adjustment by more than 5 degrees variation from center to center steering lock, i.e full L/H to R/H . That is simply put because its part of the stability control system interface.

Now this is NOT rocket science rather its the use of a professional style scan tool incorporated with oscilloscope features.
Obviously a code or two gives the clue, but switching to wave form program PID on the scan tool will allow the operator to "see' each four corner wave forms as you roll the car forward and back. Sometimes you simply drive the car up to about 30mpg with an assistant observing the wave form activity which MUST be uniform. You can't go much faster than that since these systems cut the scan tool communication for safety reasons.

If you have to as a tech be closely looking at glitches to solve a problem at speed, (say going over a road bump causing loss of communication) then a full 4 or 6 channel oscilloscope directly connected to each sensor circuit is what's needed. Now Picoscope automotive series tool at about $6500 , even has a wave form library built into it, so it can be used as a reference point for mechanic dummies who are inclined to want to shot gun the repair by guessing.
In my shop the wave form study diag' accounts for about 1 in 50 repairs involving wheel speed related issues.

The other of course is just BASIC electrical related.
Wiring bad communication due to high resistances , low supply voltages including a loss of the high speed Can-Bus circuitry.
As this is a Euro based BIG three brand (car/vehicle ) I swear the harnesses etc were made/designed by Chef Boyardee .

Now with diagnosis, brand knowledge is essential, and "some" is platform familiarity from brand to brand being "really essential" & of course knowing what you are dealing with, but ostensibly (MB in this case ) uses two distinct systems depending upon year /type /vehicle /model etc .
Here's some Sunday afternoon reading matter on the subject:-

Wheel Speed Sensors – Active and Passive

As a further comment why do shops in the UK not give the customer a print out of the scan tool results ,since many of you are paying for the diag scan tool service which costs money?.
In today's connected world its just a touch of a button to print out results, send to R/O archives. even aim the bloody scan tool at the problem area, and take a photie from the customer to see.

The other was a chuckle into my morning cup of PG Tips observing the uploaded MB dealer multi choice inspection sheet. OK by itself, but who is the team leader I ask????
Who do they think they are???
In the Royal Air Force doing the Battle of Britain thing with customer's car ???
Or is it one of those besuited individuals getting a wage for swanning about with paper in his hand !. OH me Gawd!!

Reading these posts, its a formula for a bad or inconsistent repair, & a comeback with & angry customer to go with it!
Where's team leader I ask FFS ??--He's been fired and he's left on the horse he rode in on! :eek: :wallbash: :D
Tuercas Viejas.










e

,


.
My statement about pad wear was based on the OP’s car - an eight year old W204 with 61k miles, that had been MOT tested and serviced at a Mercedes-Benz main dealer just a few days before.

It actually said:
Worn brake pads will not give an ABS fault, or indeed a fault code for a wheel speed sensor.
MOT checks include the minimum thickness of brake linings, the braking performance itself on a rolling road, wheel bearings and indeed imbalance/brake fluctuations would be picked up on this test. Likewise a main dealer would not miss a chance to increase those brake condition assessments from amber to red, or indeed other noted wear items including wheel bearings.

Your description of the braking system and diagnostics is sound, but so is the logic that W204 wheel speed sensors are prone to failure, the symptoms described by the OP and that the car has already been diagnosed with this specific fault by a mechanic :thumb:

No mention of adverse braking performance from the OP either. Surely it would in the first instance just kick the ABS/ESP systems into operation in a similar way to a loss of traction on one corner anyway - rather than a stored fault code for an implausible wheel speed sensor on one corner (?)

At this stage, I would still give credit to the original diagnosis and perhaps start with the obvious - the wheel speed sensor on the NSF - that’s where my money would be :)
 

Tuercas viejas

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Never seen pad wear trip an abs sensor fault in 25 years of working on mercs and yes we do give out the Star test print out when it’s paid for.
Is that showing a pre-repair test Diag etc, And a post repair road test print out attached to the R/O to show a successful repair?
How do you sell the job without supporting Diag evidence to the customer to verify a repair parts & sales agreement and sign the R/O contract ?
Curious??
Tuercas Viejas
 

Tuercas viejas

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On some comments and questions in this thread, and not in relation to one specific point. I'm also not intending to diagnose as I don't have any in-depth understanding. I'm just chipping this in as it might be useful knowledge.

After charging, your battery should be holding 12.7 volts (maybe a little more if it's an AGM battery) for extended periods, like days or weeks.
If it's not reaching this voltage 24 hours after charging (because it takes a while to stabilise after a charge), either the battery is duff, or you have some serious parasitic drain coming from somewhere.
At 9 years old, battery failing would be likely, but of course age isn't a 100% indicator that you don't have parasitic current drain.

Some discussion on voltage:

Someone has already suggested that low battery is mentioned in the handbook around this issue.

ECO stop/start not working is also a classic symptom of low battery.


One final point:
If you have an AGM (Acid Glass Mat) battery, you must not use the recondition function on the chargers. That is designed for normal flooded/wet lead acid batteries. It works by attempting to remove sulphate deposits off the lead in the battery by electrochemically inducing hydrogen gas generation. These gas bubbles are intended to help dislodge the sulphates.
In an AGM battery, it is as it sounds, a mat of materials, and is therefore not suited to the reconditioning phase.
Plus, the car electronics shouldn't be exposed to the higher voltage used during reconditioning because it can damage them. You would disconnect the wet lead acid battery from the car before performing this reconditioning charge.
I/We use a multi function charger that makes the operator select the right type of battery to be charged .
If you don't do that, you can wreck a perfectly good battery .

Additionally a modern battery charger has a selectable program function that holds a steady ripple free 14,1 to 14,2 battery voltage for down loading module flashes etc from manufactures' web sites over the WiFi using the scan tool as a pass thru device .
Tuecas viejas
 

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