JimVonBaden

I started this in the middle of a different thread, but thought it would make sense o post this on its own.

My 2005 CLK500 has 62,000 miles on it. Three months ago my car was parked for 3 weeks. When I got back the battery was flat. I changed the battery. It lasted a while but when flat a few weeks later after sitting a week. Definitely a draw issue. About that same time I started getting a popping sound from the dash, like an electronic valve opening and closing. It would do it on start up, then stop after about 30 seconds.

About a month ago it died at a light. It took 5 minutes of trying, but it finally restarted. I blew it off because it otherwise ran perfectly. A few weeks later it did it again. This time I had to get it towed. I killed the battery trying to restart is. I swapped out the Crank Position Sensor as suggested in the other thread. It lasted a few days, short trips, then did it again. It restarted after about 10 minutes. I then changed out the Cam Position Sensor. This time it died in 15 minutes of idling. Both sensors are Bosch.

I charged the battery fully and was working on other stuff for a couple of days, and again, dead battery. I am beginning to believe the issue is not the sensors at all, but a battery draw issue. I do get a check engine light, but no codes related to the light. The alternator is putting out 14.4 volts. I have some codes from the low voltage, but none that seem to indicate where the issue lies. Here they are:









As you can see, no ignition codes.

Lots of data, but I am lost as to where to start.

Plutoe

Load test the starting circuit-----what's the output voltage??

JimVonBaden

I'll check that tonight. Likely it is OK, as I can turn the car over at least 10 times before the battery starts to go too low.


Thanks,

JimVonBaden

Load test with a fully charged battery was 11.2V, plenty.

Interestingly, I drove it around today a few times, let it idle for over half an hour, no problem. Took it to lunch, and when I came back to the car half hour later, it wouldn't start again. It cranked, but no start. I dumped two liters of ambient temperature water over the CPS area and it started. Only potentially contributing factor is I opened the cover on the left side with the relays and pressed all of them tight. It did rain while I was eating, but everything in the box was bone dry.

I guess I need to drive it until it dies again and douse the CPS to confirm it is the issue.

JimVonBaden

So, yesterday I started it and let it run for a while. 15 minutes and it died. I poured water on the Crank Sensor, nothing. I poured water on the Cam Sensor and it started right up. It ran for 15 more minutes and died. I poured water on the Cam Sensor again, and it started right up. I suspect I got a bad Cam Sensor. I am going to play with it for a while and see if I can make it happen again.

Rudeney

A bad cam sensor should throw a code and illuminate the MIL.

JimVonBaden

I am getting a Check Engine Light. What code should I see? It would be under engine section, right?

By the way, what is a MIL? Is it the same as a CEL?

Rudeney

MIL = Malfunction Indicator Lamp, a.k.a. Check Engine Lamp (and , a.k.a. Check Wallet Indicator ). Yes, definitely pull codes. SDS is best to get the MBZ-specific DTCs, but in a pinch, a generic OBDII scanner can read ECU codes that would illuminate the MIL.

JimVonBaden

OK, so I think I was using the reader wrong (i980 from iCarSoft, made for the Mercedes). I hooked it up and went through the process, and low and behold, what do I find?





Cleared the codes, checked again, no codes. Started the car and went through all the modules clearing old codes and low battery faults from killing the battery. Within 10 minutes it does, CEL on. I checked the codes:





Again, same codes. Car wouldn't start. Cleared them, rechecked them, same codes again. Poured bunch of water on the CPS, car starts up, cleared the codes and they stayed cleared. Restarted the car, no CEL, no codes.

Seems very obvious I have a second bad CPS!

Now to order another replacement.

Rudeney

Honestly, I am very perplexed at the frequency of CPS failures. These are very simple things - they are just Hall Effect sensors which are nothing special. So why do they fail? My guess - and this is just an armchair SWAG - is that it's a combination of minute expansion/contraction issues with the flywheel (a.k.a. flex plate), bell housing and the CPS itself. When there is just too much space between the CPS and the flywheel segments, it fails. I am guessing I am now approaching about 1 million "Mercedes" miles and I've never had a bad CPS, but then there are people who have had several. It's a bit of a mystery. I do know, anecdotally, that I hear of failures of replacement CPSs when they are bought through eBay and Amazon as compared to dealers and German parts suppliers.

JimVonBaden

Agreed. It is a fundamentally simple sensor. It should not really fail with any regularity. I admit, though, that this CPS came from Amazon, and could easily have been a take-off bad one. I am getting a refund and ordered a replacement from here: http://www.autohausaz.com/search/pro...archbutton.y=8

Seems pretty certain it is the issue though. Not many times you can narrow it down with such certainty. Time will tell.

Thanks for your help and support!

Rudeney

Keep us posted as to how the Autohaus part works out. I have been disappointed with the Amazon sellers lately. I bought an oil centrifuge cover from Amazon for the SL550 and it's already leaking. I think I'm just going to buy the OE part from the dealer (well, mboemparts.com).

JimVonBaden

Will do!

91ser

Wow, never thought about dousing it in water to test!!! Good idea JVB!

Ive had one CPS fail so far. It happened at nearly 100k miles on the 500. Luckily, its a cheap and easy fix and Napa stocked the part.

I like your 1200GS. If I ever get a touring bike, ive had my eye on the BMW bikes for years.

JimVonBaden

I stole the idea from Rudeney, I think.

I already put a cheap one in, and it was defective out of the box.

Thanks, I really like my R1200GS.

Rudeney

And I stole the idea from an MB Roadside Assistance tech.

91ser

Well, hopefully I'll never need to use this trick! But if so, thx Roadside tech!! hahaha

JimVonBaden

Definitely not definitive, but 20+ in town miles in 90+ degree heat, and it didn't die. Fingers crossed the new CPS did the trick!

JimVonBaden

Another day, another 20 hot miles around town. Confidence is growing. (Fingers still crossed)

JimVonBaden

Over 100 mixed city/highways miles at 80° temps. No issues. (Fingers still crossed.)

JimVonBaden

Follow-up. Just under 1000 miles of mostly city driving and no problems. I seems confirmed that the CPS was bad, and the first replacement CPS (Bosch from Amazon) was also bad.

Rudeney

I have really begun to believe that car parts on Amazon are just a bad deal. This is at least the 10th time I've heard reports of a "Bosch" CPS or MAF sensor from Amazon failing or DOA.

I replaced the leaky oil centrifuge cover on the the SL with one from Amazon. It wasn't a genuine MBZ part, but I figured what the heck - it's just a piece of plastic with a rubber seal so how hard can it be to make them? Well, I saved $35, but it's leaking again after 6 months. I guess I'll buy the genuine MBZ part. I think I'm done buying car parts from Amazon - they're no better than eBay.

JimVonBaden

I'm beginning to think the same thing. The only exception so far is windshield wipers.