Engine not cranking. Correct test procedure? - Mercedes Benz SLK Forum

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#1 Old 10-09-2012
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Engine not cranking. Correct test procedure?

My SLK 320 engine does not crank when I turn the key to the start position - no sound, except that the engine cooling fan runs after a few seconds.
At first this problem was intermittent; it sometimes failed to crank on the first turn of the key but worked normally when I tried again. Now it won't crank at all. The battery is perfect and the connections are fine.

There is no sound from the fuel pump when I turn the key to the ignition on position.

I suspect that the K40 relay might be at fault although it looks fine, but I want to go through the correct test procedure before I replace it. I would appreciate any help, especially with the following:-

1. Should the fuel pump run for a few seconds when the key is turned?

2. If the fuel pump fails to run for a few seconds, does that prevent engine cranking? Is this controlled by the K40 unit?

3. I've tested for power at the fuel pump terminals when the key is turned to the ignition on position, and there is nothing, Where do I go from here?
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#2 Old 10-09-2012
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Try finding the starter motor on top of which , piggy back style , you'll find the solenoid . Give the solenoid a couple of light taps with say the handle of a hammer or something similar and see if that works !
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#3 Old 10-09-2012
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Thanks for the quick reply curro101, but I'm looking for a more methodical approach.
If the starter solenoid does not receive power until the fuel pump has run then my problem can't be the starter motor. That's why I need to know whether it is necessary for the pump to run before the engine will crank.
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#4 Old 10-09-2012
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Try it , can't hurt and could save a lot of looking , but it's up to you !!!
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#5 Old 10-09-2012
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How old is the battery? 9 times out of 10 that's the problem.
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#6 Old 10-09-2012
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No, the problem is certainly not the battery.

If you read my post, I explained that I'm not getting power to the fuel pump when turning on the ignition. I suspect that one of the functions of the so called K40 relay module is to supply power to the fuel pump which then allows it to power the starter solenoid. This would suggest a faulty module but it's an expensive item and I'm not going to replace it unless I'm sure it is faulty. That's why I need somebody to confirm the sequence of events during starting, or to suggest a logical test procedure.

Where is Bazzle when you need him? I suspect that he might know the answer!
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#7 Old 10-09-2012
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ditto the battery

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#8 Old 10-09-2012
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Quote:
Originally Posted by mikevernon View Post
No, the problem is certainly not the battery.

If you read my post, I explained that I'm not getting power to the fuel pump when turning on the ignition. I suspect that one of the functions of the so called K40 relay module is to supply power to the fuel pump which then allows it to power the starter solenoid. This would suggest a faulty module but it's an expensive item and I'm not going to replace it unless I'm sure it is faulty. That's why I need somebody to confirm the sequence of events during starting, or to suggest a logical test procedure.

Where is Bazzle when you need him? I suspect that he might know the answer!
I did read your post, nothing will work correctly if the battery is dead or does not have enough charge. Did you try and swap it out from another car? or put some cables on it and see if it starts? Bazzle is long gone he sold his SLK years ago. Keep us posted on what you find please.
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#9 Old 10-10-2012
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Please, please, please can anybody tell me whether the engine will still crank if there is no power being supplied to the fuel pump?

I'm suspecting a K40 relay module failure as the cause of my engine's refusal to crank. There's no power to the fuel pump and I suspect that this results in no power being supplied to the starter solenoid. Can anybody confirm this?

And PLEASE no more posts suggesting that the battery might be the cause of the problem. it isn't.
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#10 Old 10-10-2012
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well, if you don't want anymore battery suggestions, you might not like this one:

Please update your location/vehicle (model and year) in your profile as it helps the members answer your questions which usually are based on that information.
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#11 Old 10-10-2012
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Ok, just for a refreshing change, I'm not going to suggest checking the battery.

Check the battery earth terminal is making good contact with the body (and the battery end is not corroded) - a common problem on early R170s.

And please update your profile - there are a lot of country specific variations.



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#12 Old 10-10-2012
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Please don't be offended guys, but I can't understand why you keep replying to this thread with battery suggestions when I stated at the start that the battery is perfect. If you actually read the post I said that the problem was intermittent at first - nothing on the first turn of the key but absolutely normal on the second turn (engine cranks at full speed). I now have no cranking and no power at the fuel pump, but otherwise full power everywhere else.

What I'm trying to find out is whether the lack of cranking is a consequence of lack of power at the fuel pump. So I need somebody who understands how the K40 module functions.
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#13 Old 10-10-2012
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Mike,
Unfortunately you were short and abrupt with the only preson who has replied to your thread who owns a 170. This is a pretty cordial place where people from all around the world come to get help and share experiences. There are differences between cars sold in the US, Europe, Far East, and Australia,and we have members from all of those places. So far it is unclear in this thread where in the world you live.

I realize that you are frustrated with your car, but this is not a typical internet forum where people regularly flame other posters. My humble advice to you is to update your profile and be a little more cordial. There are probably people on here who know the intricacies of the K40, but you will probably have to attract them with a little honey.

Best Wishes
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#14 Old 10-10-2012
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Hi REB_TN-06

You're right, and I'm genuinely sorry if I offended anybody. It certainly wasn't intentional.
I was just a bit frustrated that some people didn't seem to make the effort to fully read and understand my post before replying. But I was guilty of venting my frustrations with the car on people who were only trying to help, so I apologise.

Anyway, back to the car. I've really grown to hate it! So if nobody can explain the function of the K40 module,who wants to buy a 2002 SLK 320 auto with a genuine 20,000 miles from new but currently very DEAD?
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#15 Old 10-10-2012
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Might be worth a try unless there's anyone in your area willing to let you try their module !!

http://www.ebay.co.uk/itm/Mercedes-B...item3a7a561669
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#16 Old 10-10-2012
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The k40 repair documented on this site is inexpensive and not too time consuming -- if you're not comfortable trying it proactively find someone who can... I'll bet you a pair of nomex underpants it'll fix your problem.

I understand your frustration with not having a diagnostic procedure to step through, but I haven't seen any such procedure for a 170 mentioned here If you write one, please post it back. I have a different car from you and I am fortunate to have a DVD-based service manual that includes wiring diagrams and Diagnostics for electrical components. I don't think the same exists for 170's.

Most of the diagnostics in the service manual are simple voltage tests though, which don't necessarily catch all wiring faults (the K40 fault is an "excess resistance" failure that a simple voltage test might or might not detect.)

And, maybe one of the reasons everybody keeps throwing "battery" out (to your chagrin) is that you didn't mention how you tested yours -- the fact that it can turn the starter normally most of the time/some of the time doesn't mean much. "Hygrometer says 90-92% on all six cells" would be better, or "I took it in for load testing and it passed" is better.

(Then again, I've tested batterys good before that turned out, in fact, to be bad).
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#17 Old 10-11-2012
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Quote:
Originally Posted by mikevernon View Post
Hi REB_TN-06

You're right, and I'm genuinely sorry if I offended anybody. It certainly wasn't intentional.
I was just a bit frustrated that some people didn't seem to make the effort to fully read and understand my post before replying. But I was guilty of venting my frustrations with the car on people who were only trying to help, so I apologise.

Anyway, back to the car. I've really grown to hate it! So if nobody can explain the function of the K40 module,who wants to buy a 2002 SLK 320 auto with a genuine 20,000 miles from new but currently very DEAD?
Careful how you vent, you never know when there is an Admin around!!
Apology accepted.
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#18 Old 10-15-2012
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The fault was the K40 relay module, as suspected. I replaced the whole module, but it was probably a failure of the relay controlling the fuel pump (2nd from left when viewed from the side with the fuses).

If my interpretation is correct, the no cranking symptom is a consequence of the failure of the K40 module to supply power to the fuel pump.
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#19 Old 10-15-2012
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Awesome news...
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#20 Old 10-15-2012
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Glad you got it sorted ...
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