Replaced fuel pump now rear SAM is bad?
#26
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2006 CLK350 Cabriolet (A209)
The problem with CPS failure is it often does not throw an error. Today's dealer techs rely 100% on DTCs to decide what part to replace. The challenge in diagnosing CPS failure is that it mimics fuel pump failure. Without a signal from the CPS, the ECU shuts off the fuel pump as a safety feature (no CPS signal = no engine rotation, so no need for fuel).
There is a breakout box that can be plugged into the ECU that allows the tech to jump out the fuel pump so that is is energized regardless of engine running or not. If doing that causes the pump to operate and produce pressure at the fuel rail, then I'd say it's the CPS (or, though doubtful, the ECU itself). Unfortunately, most techs only understand how to read codes and swap parts - they have weak diagnostic skills and little understanding of how these electronic systems actually work.
There is a breakout box that can be plugged into the ECU that allows the tech to jump out the fuel pump so that is is energized regardless of engine running or not. If doing that causes the pump to operate and produce pressure at the fuel rail, then I'd say it's the CPS (or, though doubtful, the ECU itself). Unfortunately, most techs only understand how to read codes and swap parts - they have weak diagnostic skills and little understanding of how these electronic systems actually work.
#28
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Lol, I edited. But you are right. When I picked up the car (on the day it ran) I spoke to the tech on the phone and he said it started the last 30 times, as if that means anything, and then went on to explain everything he had done. No mention made of checking the CPS. I'm sure he knew the car was not fixed, I'm surprised it started for a day. The CPS going out would logically explain all the issues. I don't care at this point that I might have needlessly paid for a fuel pump and SAM, I just want the car fixed. The car has never thrown a code and at this point their service department has lost all credibility with me. If they get their feelings hurt by my message I don't care, I just want them to put in a new sensor and see if that works. I'm assuming you can't tell if the sensor is bad or faulty by just looking at it. They had the car the first time for 20 days and gave it back and it still wasn't fixed. It is beyond frustrating.
#29
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Well, I wouldn't tick them off before they fix it - there will be plenty of time for that once it's fixed. You can then dispute the charges and threaten a crappy survey to MBUSA (these surveys directly affect their wallet).
Unfortunately, there is usually not a definitive method to detect a bad CPS except by replacing it. It's a Hall Effect Sensor, which is a magnet that passes current when it is magnetically attracted to a metal. The rim of the flywheel has alternating holes, and the CPS sits very close to, but not touching, that rim. As the flywheel turns, the CPS pulses the current as it passes over the solid parts of the flywheel. This allows the ECU to determine that the engine is still rotating. There is also one longer void on the flywheel that the ECU looks for to determine the angle of the crankshaft for timing purposes. No signal from the CPS tells the ECU the engine is not rotating, therefore it shuts off fuel supply.
I am not sure what causes the CPS to fail, but it seems that extreme temperatures can affect it. Most of the time we hear that it fails from heat, and then when the engine cools down, it works again. MB Roadside Assist techs have learned to pour cold water on the CPS to get a customer going again (and thus diagnose the problem). My guess is that the electromagnetic properties of the CPS are not failing (that would violate some laws of physics), but maybe it's a slight physical warping of the sensor or even the bell housing so that it moves just far enough away from the flywheel that it can't sense properly. It's also curious that some cars never have this problem, yet others have it multiple times. And that cheap knock-off CPSs also fail more often, or just don't work at all. To me, that just says it's a tolerance issue.
Unfortunately, there is usually not a definitive method to detect a bad CPS except by replacing it. It's a Hall Effect Sensor, which is a magnet that passes current when it is magnetically attracted to a metal. The rim of the flywheel has alternating holes, and the CPS sits very close to, but not touching, that rim. As the flywheel turns, the CPS pulses the current as it passes over the solid parts of the flywheel. This allows the ECU to determine that the engine is still rotating. There is also one longer void on the flywheel that the ECU looks for to determine the angle of the crankshaft for timing purposes. No signal from the CPS tells the ECU the engine is not rotating, therefore it shuts off fuel supply.
I am not sure what causes the CPS to fail, but it seems that extreme temperatures can affect it. Most of the time we hear that it fails from heat, and then when the engine cools down, it works again. MB Roadside Assist techs have learned to pour cold water on the CPS to get a customer going again (and thus diagnose the problem). My guess is that the electromagnetic properties of the CPS are not failing (that would violate some laws of physics), but maybe it's a slight physical warping of the sensor or even the bell housing so that it moves just far enough away from the flywheel that it can't sense properly. It's also curious that some cars never have this problem, yet others have it multiple times. And that cheap knock-off CPSs also fail more often, or just don't work at all. To me, that just says it's a tolerance issue.
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2006 CLK350 Cabriolet (A209)
I mentioned the CPS when the car was first taken in. When it went back after starting for only one day I sent the service rep a text message containing part of the explanation regarding the CPS that Rodney wrote here. Yesterday the service rep text me again and said the car was starting every time but they were still trying to diagnose the problem. I text back "have you checked the CPS?" I got a text back that said he would instruct the tech to check it, which I assume will mean they will replace it. Why they have ignored this for almost 30 days now is beyond me. Maybe if it is the CPS could it mean I really didn't need a new fuel pump? Or is the tech just too lazy to tackle the job? I don't believe that the car is starting "every time" either. The last time they told me that it only started 5-6 times and then quit. A bad or failing CPS would logically explain the intermittent starting. So yes, I agree with you, it should have already been replaced on the first visit to the shop. After all it is a 10 year old part that has lived its life in the Texas heat.
#32
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If this turns out to be the CPS, I would absolutely DEMAND that the dealer refund all money paid! CPS failure is such a common problem, they should know to consider that first. If not, then they are just trying to pad their revenue number with unnecessary repairs. In a way, I hope it's not the CPS because I don't want to believe that the shop is either that ignorant or that untrustworthy.
#33
Speaking from experience. The 272/273 crankshaft position sensors were extremely reliable in comparison with the 112/113. However, up until sometime in 2007 there were some that failed and there was a shop Foreman conference call that covered this topic about a crank no start with no codes and it mentioned a date range to look for stamped on the sensor. It's very possible you have one of these affected sensors.
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2006 CLK350 Cabriolet (A209)
If this turns out to be the CPS, I would absolutely DEMAND that the dealer refund all money paid! CPS failure is such a common problem, they should know to consider that first. If not, then they are just trying to pad their revenue number with unnecessary repairs. In a way, I hope it's not the CPS because I don't want to believe that the shop is either that ignorant or that untrustworthy.
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Speaking from experience. The 272/273 crankshaft position sensors were extremely reliable in comparison with the 112/113. However, up until sometime in 2007 there were some that failed and there was a shop Foreman conference call that covered this topic about a crank no start with no codes and it mentioned a date range to look for stamped on the sensor. It's very possible you have one of these affected sensors.
#36
Rocman8 - This could be very useful information, just want to clarify you are referring to the camshaft position sensor (CPS) that is accessed from the top of the engine bay? I remember reading about a crankshaft position sensor also, I believe it is referred to as a "CKP" sensor? I know there is confusion regarding the two sensors, myself included, so want to make sure we are talking about the same part. Thanks, Mike.
#40
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Useless dealership that is. Once you get the car back, if I were you, I'd tell them to hire new technicians or close the dreaded place. I am sure that in SDS, there must be a place to test the sensor in diagnostic mode like we do. It should be able to indicate whether the signal is low or high when its close or far from metal. Obviously they should conduct the test not once but several times for prolonged durations to inspect their observations and compare if they are the same or not in ruling out a faulty sensor. However I am unsure if this is possible but if my company equipment can conduct this test, MB surely can as well.
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Useless dealership that is. Once you get the car back, if I were you, I'd tell them to hire new technicians or close the dreaded place. I am sure that in SDS, there must be a place to test the sensor in diagnostic mode like we do. It should be able to indicate whether the signal is low or high when its close or far from metal. Obviously they should conduct the test not once but several times for prolonged durations to inspect their observations and compare if they are the same or not in ruling out a faulty sensor. However I am unsure if this is possible but if my company equipment can conduct this test, MB surely can as well.
#42
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Rodney, do these cars have a fuel pressure sensor that will trigger a code? I ask only because I changed the pressure sensor on my wife's XC90 when it triggered a generic OBDII code for low pressure at the rail. I was just wondering if even though the CPS throws no code, would a bad fuel pump, but good CPS, result in some code such that the absence of a code might be diagnostic of a bad CPS and not a bad fuel pump?
#43
Rodney, do these cars have a fuel pressure sensor that will trigger a code? I ask only because I changed the pressure sensor on my wife's XC90 when it triggered a generic OBDII code for low pressure at the rail. I was just wondering if even though the CPS throws no code, would a bad fuel pump, but good CPS, result in some code such that the absence of a code might be diagnostic of a bad CPS and not a bad fuel pump?
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Got a text from the service rep today saying the car has been starting every time and there is nothing to diagnose because the car is starting, but do I have a spare key? Replied yes I have a spare key and could drop it off and btw, when it wouldn't start here I tried the other key and it still wouldn't start. Within minutes I get a message back that the car is not starting after all and they will run diagnostics. Oh, and hang onto the other key for now since I had tried it already when the car wouldn't start here at home. At least the tech is thinking as far as the key and its associated electronics, now if I could just get him to the CPS...
#47
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this is your car right? why do you just demand that the replace the cps. Tell them if it still doesn't start you'll pay the $100 for the part.
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The service rep asked for the spare key today which I dropped off. While I was there I brought up the CPS and that it could fail and not throw a code and there was no way to test it without replacing it. Another rep was there and politely told me I was wrong, that plenty of cars came in showing a bad CPS code. So that was the end of that conversation.
#49
Yes, it is my car. However, since I have already paid for the fuel pump and SAM my agreement with them is that if those parts didn't fix the car (which they guaranteed would fix it) then anything else is on them. So I'm not in a position to demand certain parts be replaced at this time.
The service rep asked for the spare key today which I dropped off. While I was there I brought up the CPS and that it could fail and not throw a code and there was no way to test it without replacing it. Another rep was there and politely told me I was wrong, that plenty of cars came in showing a bad CPS code. So that was the end of that conversation.
The service rep asked for the spare key today which I dropped off. While I was there I brought up the CPS and that it could fail and not throw a code and there was no way to test it without replacing it. Another rep was there and politely told me I was wrong, that plenty of cars came in showing a bad CPS code. So that was the end of that conversation.
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2006 CLK350 Cabriolet (A209)
I used to have a trusted service rep at this location but he moved to a different location that is across town and too far away. I don't know if this is just happening at my dealership but it seems my dealership does not want to actually speak to service customers anymore, all communication is done by text or email. If I call the phone is never answered but goes to voicemail, however the last few times I have been in the service rep area I noticed I never heard a phone ring. Even payments can now be made in advance online. Maybe this is how things work now but sometimes you need to be able to speak to an actual person.
The new service reps are not like the old ones. Less than a year ago I went in for new spark plugs and was advised I needed a new battery. My service rep that day was a young girl who was obviously new, I told her I always keep my old parts and I wanted them put in the trunk when they were removed. When she informed me about the battery I renminded her I wanted my old parts put in the trunk. She said in the trunk and sounded confused, I said yes in the trunk. I get a text the car is ready and go pick it up, check the trunk and there are the parts and head home. It is getting dark already when I go to the car to put the old parts in the garage. I'm not paying too close attention but I pick up the battery and think this looks really clean, I don't bother to check out the spark plugs but notice they were put back in the new box. That night I kept thinking how good my old battery looked and went to bed still puzzled by it. The next morning I was still thinking about that battery, and then the light bulb went on...could that really be the new battery? No, how could that be? Well, it was the new battery and the new spark plugs. I looked closer at the invoice and sure enough I was not charged for labor, just parts. It was easier to install them myself than go back and deal with that service rep again. How a simple request for the old parts be put in my trunk got translated to don't install the new parts but put them in the trunk is beyond me. Is it that unusual to ask for your old parts?