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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 20357
Experience:  BEng hons Mech engineering, in auto industry 22 years
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All, I have a 2007 s'class 302L cdi, and at the moment

Customer Question

Hi All, I have a 2007 s'class 302L cdi, and at the moment every time I slow down or brake just before it stopping I feel a jerk . this is happening all the time for the last two days , now the engine icon has comes on and stays on in yellow. any idea what is going on and how to solve this problem...?? I did have the glow plugs 1 & 2 changed about last year November 2015. please any real ideas to help would be most grateful. Thanks
Submitted: 8 months ago.
Category: Mercedes
Expert:  Matt replied 8 months ago.
Hello On any car if you get a check engine light or other fault light this typically means one or more of the sensors has failed or has a faulty connection. The fault can be something quite simple and nothing that’s going to stop the car to something quite major that will reduce engine power and possibly stop the engine The ECU senses this and may put the car into 'limp home' mode which typically limits the revs and the amount of power available. Usually the car is safe to drive for a short distance as the mode is intended is intended to get you home without incurring any engine damage The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious. to get the jerk you describe I'd 1st check for an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running. Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Expert:  Matt replied 8 months ago.
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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 20357
Experience: BEng hons Mech engineering, in auto industry 22 years
Matt and other Mercedes Specialists are ready to help you
Customer: replied 8 months ago.
Hi Mat, sorry for the delay in replying to you, in the end I took it into the dealership MB, I've since had the updates put on my car , two small f on the diagnostic. One could be a possible injector, and the other a sensor around the exhaust. It feels and drives better after the updates on the car but they said i must keep an eye on it, so at the minute they are saying don't throw no money at the problem as yet. But what would you suggest for squeaky brakes....?? If that ok with you many thanks .
Expert:  Matt replied 8 months ago.
Brake squeal is caused by the pad vibrating at high speed on the disc you should find under a hard stop the squealing stops.
Its quite common in high performance cars and there are a few things to try and solve it:
1) strip the calipers down, remove the pads and clean out all the pad grooves and location in the caliper, smear a thin layer of copper grease on the metal back of the pads where they touch the piston and where they rub in the tracks of the calliper also clean the calliper tracks of debris and dust before re-fitting the pads.
The copper grease won't melt under hi temps so DO NOT get it on the brake disc or friction face of the pads, it does however keep the brakes working smoothly and help reduce any squeal as it damps things out
2) As above but fit an anti-squeal shim as well, these are a either stainless steel shim or sticky plastic pad which fits between the piston and pad and also acts as a vibration damper.
3) file a small chamfer on the leading edge of the pads as this encourages the pad to sit squarely on the disc and not point load on one edge

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