W211 SRS question

[moj91]

We have a W211 E220 CDi estate with the dreaded SRS light on atm. Icarsoft points to the NS sensor on the front bumper impact bar (i know, a proper STAR read is needed )

As its the pita one to get to of the two we cant check the cable continuity/clean the contacts to see if that rectifies the problem, so, as we are struggling to get time to have the car off the road, i am trying to do some pre-emptive work...

Merc Northampton have given me 2 part numbers of what the sensor could be by VIN search on EPC, one a Bosch sensor, the other a ? sensor.

I am told these sensors, if it indeed need replacing must be replaced like for like by manufacturer and Part No, as we cant get to the sensor atm, in order to save the car being sat dismantled whilst we wait for parts, is there any way of telling which sensor it might be? ie. If the sensor is Bosch, will the whole SRS system be Bosch components, or the other make of parts? in so that can i check another, more easily accessible part of the system such as the SRS module under the ash tray (i believe) to see what make it is and order the same make for the sensor?

I hope that makes sense!
Thanks!

 

[Wighty]

Hi buddy , I went into this a while ago , as I have a dodgy front impact sensor which is on an upright beside the radiator . But mine hasn't played up for 6 months so I'm leaving it until it does . Yes you are correct you have to replace with the same make . My reading up on this problem and advice from others is that the sensors do fail , so just replace them , it's probably not the wiring .
If I were you and wanted limited downtime , then buy both sensors and doesn't open them until you see which make you need , then return the other unused one .

 

[moj91]

Hi buddy , I went into this a while ago , as I have a dodgy front impact sensor which is on an upright beside the radiator . But mine hasn't played up for 6 months so I'm leaving it until it does . Yes you are correct you have to replace with the same make . My reading up on this problem and advice from others is that the sensors do fail , so just replace them , it's probably not the wiring .
If I were you and wanted limited downtime , then buy both sensors and doesn't open them until you see which make you need , then return the other unused one .

Hi Wighty, I was planning on buying both, but there is one which is around £30 and the other £150 - our local dealer wont accept special order electrical part returns, even if un-opened :/ typically they hold neither in stock...

 

[Wighty]

Hi Wighty, I was planning on buying both, but there is one which is around £30 and the other £150 - our local dealer wont accept special order electrical part returns, even if un-opened :/ typically they hold neither in stock...

Jesus buddy , that's not much of a service . Will they order both in and reserve them awaiting collection ?

 

[LostKiwi]

Jesus buddy , that's not much of a service . Will they order both in and reserve them awaiting collection ?

Quite common I'm afraid. Inchcape are the same.

As to the original question as far as I'm aware there is no guarantee the same brand parts are used all the way through.

 

[moj91]

I can see why they wont allow electrical parts back, as people like me would buy each which could be at fault, and trial and test them until they find the culprit, then return the others which by then are technically used.

That's a pain LostKiwi, I was hoping to avoid having the car apart awaiting a new sensor, MB wont stock in or reserve both parts for us whilst we find out which is needed. Typically the MOT is due in 2 weeks and we haven't got 5 minutes, let alone a few days spare to have it off the road to work on it. I am going to get it STAR read through to be certain its that part... Looks like a right PITA to get to, undertrays, bumpers, headight, headlight frame all need to come out

 

[Ricardo_e220]

Mine which was a 2009 had this and I believe ended up being the cheaper one, my indi did it for me and total repair was £150 including the diagnostics stuff.. he also said no way of telling which piece until he had the car in the shop

Don’t you have another way of taking car off road and finding the correct one otherwise it would be cheaper taking it somewhere?

 

[John Laidlaw]

My local indy has a deal with his MB Parts main dealer whereby he can ‘try and return’ until he solves issues. I know this as we spent an age trying to get the flappy paddles working on my SL when I bought it (known problem when I bought it), tried all sorts until a new steering column module was changed over which solved it....all other bits were returned no charge. I doubt MB would do that for individuals though and I can fully understand why!

 

[moj91]

We had another look today - we think we can access the bolts holding the sensors on from the engine bay side, (albeit tight). They are both clear to see but the part numbers are on the side facing the chassis member, so even with a mirror we cant obtain the correct part until the sensors are un-bolted. We are going to have a crack at removing them tonight, and then try to solve the fault tomorrow assuming we have the correct sensor. At present we have no idea if it is the NS or OS sensor at fault as we cannot fathom if the B48/2 code is the NS or OS side on a RHD car. Im going to check cable continuity at the same time. We are half expecting to find a plug full of corrosion or something anyway...

 

[moj91]

So.. fixed!

ICarSoft gave a B48/2 fault code, throwing up the SRS light and a screen message which would not clear. The issue was indeed the B48/2 sensor located on the metal upright(s) either side of the radiator.

Having looked at WIS, it suggests a frontal strip down (headlights out) on the larger engined models, however our E220 had plenty of space due to the smaller engine to just reach in behind the headlights. (The driver's side sensor needed the airbox intake pipe removing but this pops out quickly enough).

I diagnosed using the novice's friend, the ICarSoft, which we found adjusted its readout to give the correct side for a RHD car, in so that it said the B48/2 was the passenger's side, and it was (We checked by swapping the sensors side to side and re reading) I had expected the issue to read as the passengers side, but actually be the drivers side as MB's are designed LHD, alas not, although I can't be certain if this will apply to all models/code readers. (B48/1 in this case was the driver's side sensor).

The sensor was held on by two short 10mm hex bolts, sprayed and soaked with some WD40 prior to lessen the risk of the rust on them damaging the captive nut on removal. There is a little pin on the sensor which slots into a guide hole to make re-positioning easier as visibility is poor. We found on the 11 year old car that the sensors plugs were clean still and had not let in water which was good and ruled out a poor connection. The were sprayed with contact cleaner regardless. The plastic cable connectors/plugs which attach to the sensor were beginning to get brittle so care was taken when un-clipping and removing/replacing them.

The main issue we had was determining what sensor the car is fitted with prior to removal and replacement - either a Bosch sensor or Temic sensor. The part numbers are on the side of the sensor attached to the metalwork so cant be seen before removal. It turns out that the Bosch sensors have a white coloured back, visible without taking the sensor off, and the Temic ones are all black. If you can see down behind the headlights, this should be visible.

It is correct that the sensors must be of the same manufacture as the original (only replace Bosch with Bosch etc.) However the corresponding part number only needs to be the same or a newer superseding one. I was told by MB that the whole system will be one manufacturer or the other, but I do not know for certain.

Once the sensor was replaced, the SRS system re-set itself after a 2nd restart of the car, although ICarSoft will reset it also.

Due to the cost of the sensor (£120) we opted to only replace the faulty unit - the other side being easy to get to when needed on the E220. On the larger engined cars which may need a greater frontal strip down to access, I would advise doing both if they are original, as I was advised that when one sensor goes, the other is usually soon to follow.

It turned out that when we reserved the Bosch sensor, MB had a delivery that morning and the chap on the desk gave us a box of sensors instead of just one - so if the other was at fault we would have been sorted for parts. The remainder were of course returned the following morning as I did not fancy a grand adding to my account invoice ha!

Hopefully this is helpful to others, I'm afraid i did not take any pictures as by the time we got round to doing it the light was going for the evening and it was difficult to get a camera in there to see anyway!!

 

[Wighty]

So.. fixed!

ICarSoft gave a B48/2 fault code, throwing up the SRS light and a screen message which would not clear. The issue was indeed the B48/2 sensor located on the metal upright(s) either side of the radiator.

Having looked at WIS, it suggests a frontal strip down (headlights out) on the larger engined models, however our E220 had plenty of space due to the smaller engine to just reach in behind the headlights. (The driver's side sensor needed the airbox intake pipe removing but this pops out quickly enough).

I diagnosed using the novice's friend, the ICarSoft, which we found adjusted its readout to give the correct side for a RHD car, in so that it said the B48/2 was the passenger's side, and it was (We checked by swapping the sensors side to side and re reading) I had expected the issue to read as the passengers side, but actually be the drivers side as MB's are designed LHD, alas not, although I can't be certain if this will apply to all models/code readers. (B48/1 in this case was the driver's side sensor).

The sensor was held on by two short 10mm hex bolts, sprayed and soaked with some WD40 prior to lessen the risk of the rust on them damaging the captive nut on removal. There is a little pin on the sensor which slots into a guide hole to make re-positioning easier as visibility is poor. We found on the 11 year old car that the sensors plugs were clean still and had not let in water which was good and ruled out a poor connection. The were sprayed with contact cleaner regardless. The plastic cable connectors/plugs which attach to the sensor were beginning to get brittle so care was taken when un-clipping and removing/replacing them.

The main issue we had was determining what sensor the car is fitted with prior to removal and replacement - either a Bosch sensor or Temic sensor. The part numbers are on the side of the sensor attached to the metalwork so cant be seen before removal. It turns out that the Bosch sensors have a white coloured back, visible without taking the sensor off, and the Temic ones are all black. If you can see down behind the headlights, this should be visible.

It is correct that the sensors must be of the same manufacture as the original (only replace Bosch with Bosch etc.) However the corresponding part number only needs to be the same or a newer superseding one. I was told by MB that the whole system will be one manufacturer or the other, but I do not know for certain.

Once the sensor was replaced, the SRS system re-set itself after a 2nd restart of the car, although ICarSoft will reset it also.

Due to the cost of the sensor (£120) we opted to only replace the faulty unit - the other side being easy to get to when needed on the E220. On the larger engined cars which may need a greater frontal strip down to access, I would advise doing both if they are original, as I was advised that when one sensor goes, the other is usually soon to follow.

It turned out that when we reserved the Bosch sensor, MB had a delivery that morning and the chap on the desk gave us a box of sensors instead of just one - so if the other was at fault we would have been sorted for parts. The remainder were of course returned the following morning as I did not fancy a grand adding to my account invoice ha!

Hopefully this is helpful to others, I'm afraid i did not take any pictures as by the time we got round to doing it the light was going for the evening and it was difficult to get a camera in there to see anyway!!

That is an excellent write up . Thanks for taking the time . Well done .

 

[LostKiwi]

Great news.