mwolf5682

Our 2009 ML350 4matic has just been examined by the local dealer under the booster recall.

They removed rubber band around booster, found 3 rust marks greater than 15 mm. When I looked, no rubber band present and little to no corrosion visible on booster.

They performed brake power guided testing of ESP control module. Brake booster failed pedal travel test, only traveled 32 mm. Performed test again and pedal travel failed again. Booster is faulty, no parts available at this time.

I am using vehicle as there are no parts available at this time. Oddly, when I picked up truck, I now have ESP inoperative light and need to depress brake pedal to shift out of park message. These were not present when vehicle was taken in.

DTC Codes are per CarSoft:

5141 B34 sensor A7/7s1 BAS release switch Plausibility
C312 Event signal stop lamp switch on CAN bus not present or is faulty
5186 Check component A7/7b1 (BAS diaphragm travel sensor)

I have cleared codes, reset steering angle and they come back. The ESP inoperative light on dash is intermittent.

Could these events be related? Booster test and now EPS inoperative?
What is a guided brake test?

What are the incentives behind this recall, it seems as is the local shop would love to replace the booster on MBZ dime, on the other hand, if it is defective I am grateful to have it repaired.

With the unavailability of parts, and it being a no drive recall, this has escalated quickly.

Any advice?

Cheers

mwolf5682

What is a guided brake booster test? Does engine need to be running to provide vacuum to booster during test?

Do the above DTC suggest that there are issues with the stop light function in the booster?

Could increased travel during test lead to DTCs that are now being seen? Is there a leak in booster that would cause these results?

It is odd that none of these problems were present prior to the xentry testing, yet on very first drive they appear. Just curious.

HPDECLK55

I can't believe they released the car like that. wow.

scoutman

This is so disappointing to hear. MB is failing us. I would be very angry with the dealer for screwing up your car. Did they have any idea when they will repair your booster??

mwolf5682

Still no booster repair. Called dealer, they have no information.

Sort of crazy, Vehicle is no drive fail and there has been no reach out or how ya doing from Mercedes.

lkchris

The “ incentive” behind this recall is that the Federal Government has ordered Mercedes to perform this recall.

Having failed the test, there is no way you should be allowed to drive this vehicle.

The rest is irrelevant.

mwolf5682

I agree.

Does anyone know how the testing is done? Does the technician apply the brake and read out the travel manually, or is there a Mercedes automatic protocol that pressurizes and records automatically.

The booster itself with the enhanced braking system and travel measure/brake switch should be less of a mystery. Is the loss of vacuum such that manually the brakes will not function? Or is it that the loss of vacuum means there is no enhanced braking pressure in emergency? Seems as if a stout braking resrponse would still be transmitted through the master cylinder. Perhaps this is why Mercedes has not approached this as a huge crisis.

It would be nice to know how many failures there are? Must not be too many, as I feel somewhat abandoned. Numbers must not be there, or we would see more action and concern for the owners.

AchuMD

In my case, we rented a car at MB expense for three weeks. Germantown MD USA

lkchris

The rust will usually if not always be on the bottom … which you can’t see … unless maybe using a mirror.

Have not seen it officially admitted, but I think the rubber band is the cause of the rust. The facilitator, of course … trapping moisture. Yes, it isn’t going to be replaced.

E55Greasemonkey

If the rust were severe enough, upon emergency heavy braking, the two halves of the booster could separate and you'd just be pushing the outside half further away, with NO braking occuring. I've never seen or heard of such a failure myself but obviously it is possible.

lkchris

it’s very simple … they cut off the cosmetic rubber band that hides the center seam of the booster and inspect it for evidence of rust. They have guidelines for measuring the sizes of the rust spots. The rubber strip is held next to the VIN sticker in the door jam and photographed. Photo is sent to either Mercedes or NHTSA (don’t know). There is no mechanical or electronic testing of anything.

if car passes, a white paint mark is applied to booster.
there is a middle solution where you are required to return in some time period
if complete failure, vehicle is impounded

E55Greasemonkey

Incorrect; if the visual rust inspection fails then there is a test performed using certain Xentry parameters from the brake booster, and physically pressing down on the brake pedal with nearly impossible foot pressure for most people. If THAT test fails, the car cannot (should not) be driven. Some cars from the rust belt with rusty brake lines have been reported to rupture due to the extreme pressure applied to the brake system during this "test."

mwolf5682

Good news. Boosters are in. Truck is in shop right now getting booster replaced.

Still curious about the booster travel test. That was the parameter that read out as a fail. After the rust spots.

The service manager did not seem to be well versed in the workings of the booster, and insisted that if it fails there would be loss of brakes. This seems at odds with the mechanical connection to the master cylinder. Yes more pressure, but I would think you would still be able to brake.

The rupture issue as you mention, may be the problem, but it seems that hydraulic pressure would be related to master cylinder travel and independent of the booster. I thought the booster just made it easier to get travel in the master cylinder piston.

Any brake experts to weigh in? I remember switching out our W163 booster, had the actual leak that you could hear, but was not recalled. Seems like something more than just air leak is involved.