Brake Pad Change and the SBC

[e220estate]

Yep, just raised the lid and on the left wing there is this large finned alloy box with the words SBC cast into the front - just like a threat! And my handbooks only show one large battery under the load area. While checking these I noticed that there is a simple procedure to disconnect/connect the battery - but a radio code is mentioned so presumably I need the original unit code to get it working again?

 

[reflexboy]

Did you not get a fault code unplugging the multi plug?
I was under the impression that happened and the code had to be cleared on STAR.
Its good news if that isn't the case

Nope-No error codes at all and no problems. The reason I did this instead of disconnecting the batteries as I was worried it would upset/reset other things. I'm no expert, but it worked for me

 

[OneForTheRoad]

so long as all the doors are locked and the keys are impossible to be able to open the doors , its just like doing any other car tbh . like I said earlier get the piston clamped with the wind in tool and you've all the time in the world , if the system fires in the tool will hold the piston in for you .

 

[e220estate]

A bit more research suggests that there might be an Auxiliary Battery under the pollen filter housing so will have a look and disconnect that as well - I can't see any downside for disconnecting the power as long as it all boots up again when I reconnect (SBC too!). My concern is receding though not fully resolved!

 

[OneForTheRoad]

Should find the other battery under the cover right hand side of engine bay , if you go down this route , windows and possibly the roof if fitted will need resetting , as will the clock , my stereo had no code to be entered . sbc will be fine once powered up keep pressing the pedal until you get a pedal , wont take long , seconds infact .

 

[e220estate]

Right...Loins girded and will probably crack-on tomorrow AM if not raining (yeah, right!).Any other thoughts pse don't hesitate to educate me further! Thanks all. Brian

 

[e220estate]

Ok - done it but I still have a bit of work-in-progress to resolve. I disconnected both batteries and left the car for 60 mins to be sure (can the SBC fire without any power connected at all, I wonder?) and it was pretty straightforward after that. Started with the off-side and the carrier bolt came out OK and the piston assembly swung away as it should. Pads came out OK and it was clear that the wear sensor had made contact with the disc hence why the warning message 'Brake Wear'. It took some fiddling to get the wear sensor out and it looked a bit knocked about (see later). Bit of a clean up, put the new pads in (question 1: the pads I removed seemed to be in a metal case/shim which was riveted to the back of the pad - the pattern replacement ones didn't. Is this likely to be a problem?), put back the wear sensor, bolted everything up and put the wheel back on. Started on the near-side and the first thing I noticed was that there was no wear sensor or wiring for one (question 2: Is this the standard on the Bosch disc brakes?). Anyway, replaced the pads on this side (again the old ones sat in a metal case/shim), bolted everything up and put the wheel on. Connected both batteries at this point and the SBC pump actuated as I did it. Sat in the car, turned on the ignition and.....STILL got the 'Brake Wear' warning message. A bit more research suggested that this is not a message you can re-set (because it is down to the earthing of the wear sensor, I suspect) and the likely cause is using a previously 'used' sensor. Previous installations I have dealt with have been one-wire sensors. When the metal of the sensor touches the disc it is earthed and the warning light comes on. But the M-B sensor has 2 wires. From what I can see on a picture of the sensor I have ordered, the two wires are kept apart by a plastic insulator - which melts on contact with the disc - and it's the touching of the 2 wires in the sensor which triggers the 'Brake Wear' message rather than earthing to the disc (question 3: am I right in this?). Removing the message is my current work-in-progress - hopefully will go when I replace the wear sensor.
Anyway, went out to try things and everything works fine so the car has successfully re-booted!

 

[whitenemesis]

Regarding SBC operating with both batteries removed, just be aware the system reservoir is pressurised to approx 1600psi, any stored pressure may be released if triggered?

 

[OneForTheRoad]

if you've ordered a sensor , snip the wires at the pads end and join them together , this will rid you of the message for now , was there no plug socket bolted to the other calliper ??? the pagid pads I used had the metal casing on them, you also get the wear sensors .which brand did you buy ???

are your windows auto up and down with a single button press ???

 

[e220estate]

Had decided that tomorrow AM I would unplug the sensor and see what happens. If I still get the message I will try your suggestion. Absolutely nothing on the near-side calliper. Not even a wire leading to a plug in front of the sensor - the clip on the hub carrier only has the ABS sensor wire in it, the other part of the clip is empty! As to make, they are Eicher. The tang which fits into the upper/lower locating clips is the width of the old pads PLUS the metal case/shim ie it is the same width, overall. Pagid next time then , and I hadn't really understood that the warning message implies that the sensor had been 'consumed'!

 

[e220estate]

Ohhh..windows were one touch up/down but have not tried them yet!

 

[OneForTheRoad]

you,ll be a pad change expert soon then using eicher pads , they wont last that long , they are cheap for a reason and will soon turn to dust , they should be made illegal tbh , the friction material has been known to break free from the backing plate , they are so poorly made . their discs are ok , but the pads are a big no no , especially in a car like yours . I fitted them to a 1.9 pd vw Passat once , changed them again after 2 months , total crap .

joining the wires together on that sensor will turn off your message , its an open circuit when the sensor rubs on the disc that turns it on .

 

[e220estate]

Thanks for the info - will see how it goes but won't be surprised when the message comes up again - at least I will get quicker at it!

 

[andy27168]

Hi,
Something no one has mentioned, including me is that the batteries need to be disconnected/reconnected in a specific order, boot/large battery first, then the small one under the bonnet, and then reconnect the small one first then the large battery.
If this isn't done it can cause problems.

 

[e220estate]

Well....I disconnected the aux one first and the boot one second and reconnected the boot one first and the aux one second (btw the Haynes manual doesn't id a necessary sequence) - so watch this space! I wonder why the M-B handbook makes no mention of the aux battery (ie symptoms of it's failure)? It can't last forever!

 

[andy27168]

Hi,
I have been having recent issues with my batteries, and spoke to a friend of mine who works for a Mercedes main dealer he stated that if any issues with the batteries then they would look at the date stamps on the batteries and if over fours old replace them, though think that was based on AGM batteries being fitted. My car MB no longer spec an AGM battery (CLS55) for it just a normal Lead Acid, so I just left it on charge for a day or two and did a drop test on it which proved it was ok, the date code on top of my small battery was over four years so was just replaced.

 

[OneForTheRoad]

I'm thinking the leads to the smaller battery are live from the main all the time , that's why its best to d/c the main first ???

no harm in giving the small battery a 12 hour charge on a 4 amp charger just to freshen it up .

 

[whitenemesis]

There is no direct connection between the two batteries. The Aux battery is brought into circuit by the aux battery relay, controlled via the BCM

 

[e220estate]

Two independent battery's? - I have never come across this before my M-B. What functions are supplied under what circumstances by the aux. battery? Or, putting it another way, what won't work if the aux. battery isn't up to it - this would help id aux. battery failure, it seems to me? All interesting and helpful stuff.

 

[whitenemesis]

In the 211 & 219 the aux battery is simply there to support the main battery, should the system voltage drop too low the BCM will switch in the aux battery by closing the aux battery relay. The BCM also constantly monitors the charge in both batteries and directs the alternator charge current to where its needed, almost always to the main battery as in normal operations the aux is never used.

Have a read here http://bayhas.com/mercedes/w211/contents/electrical/elect_battery.htm

In the 230 its slightly different as the front mounted battery is for starting the car and is directly connected to the starter motor.