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K40 relay module

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#201 ·
Still no start

I fixed my K40 module once before and all was fine for 6 months. Same typical K40 problem now again, so bought a new one, plus replaced my 8 year old battery that wouldn't hold a charge. Bottom line no start and now "start error" message. Any thoughts? Stuck in garage and don't want to tow to repair. I the "start error" a different problem?
 
#202 ·
No SC operation and EPS/BAP with CEL.

These are 2 of the symptoms my car has intermittently. Once it has heated to normal the BAP/EPS will go out and I get SC operation again. think this is it? I cannot check myself due to health issues but will try nit if it is familiar with my new thread on my issues. THX! Mark
 
#203 ·
Absolutely and hope everyone understands this point. I'm an engineer and have been manufacturing PCBA"s for over 20 years and swore my K40 was good and performed solder touch up anyway. Swapping the K40 fixed my problem. When in doubt save yourself time and just buy a new one.

peter@cyberpage.co.za said:
Be aware that what looks like a perfect solder joint could still be a cold joint, especially if the connector is not clearly visible on the outside of the solder blob
Click to expand...
 
#204 ·
Shanghai_todd said:
Absolutely and hope everyone understands this point. I'm an engineer and have been manufacturing PCBA"s for over 20 years and swore my K40 was good and performed solder touch up anyway. Swapping the K40 fixed my problem. When in doubt save yourself time and just buy a new one.
Click to expand...
Sorry Peter but I really have to disagree with you here. Yes the K40 is a horribly unreliable component and Mercedes should be ashamed of themselves, but I really hate this approach to solving problems by trial and error. There are lots of people on here who will rush out and needlessly replace their K40 just because one of their car's symptoms is similar to a post in this thread, in the hope that it will solve the problem.


As an engineer you should know that the correct approach to solving any problem is through a logical test procedure, not through randomly replacing components in the hope that you will stumble across the solution. And most components, including circuit boards, can be tested before replacing them. There's no rocket science involved.
 
#205 ·
mikevernon,

Do you have any such test procedures? I'm sure there are some, but I've never seen them. There are five relays internal to the K40: fuel pump, horn, radiator electric fan, AIR pump, and ETS/ASR, but I don't know how to test all of them.
 
#206 ·
efair said:
mikevernon,

Do you have any such test procedures? I'm sure there are some, but I've never seen them. There are five relays internal to the K40: fuel pump, horn, radiator electric fan, AIR pump, and ETS/ASR, but I don't know how to test all of them.
Click to expand...
Some time ago, after tons of digging, I found a thread which mentioned the resistance of each. For some reason, everyone would rather spent 100-200 for a new relay as opposed to bench testing first.
 
#207 ·
Another +1 for just replacing the module. I too tried re-soldering every connection to no avail. I will bench test the dud to determine the true cause, but I spent hours of troubleshooting time, and hours of research, far exceeding the $152.00 shipped from driveoemautoparts.com
Put it in the car which has not started in a month (I travel a lot), and fired on first crank.
My suspicion is the fuel pump relay energizing coil is open, or the circuit feeding it is.
 
#208 ·
So a friend of mine ask if I can take a look at his neighbors SLK who was having random no-starts but would start up when hooked to the charger with the 250amp quick jump. So 1st thing I do is open the K40 and find the relay furthest to the right rusted and corroded. solder joints and rest of the PCB looked OK so I cleaned the relay with some diet coke and wire brush and recommended he replace it. It was starting up while I was there and got a case of beer out of the deal.


Not sure if this was 100% of his problem but I don't think the rusted spring and contacts were helping anything either..





 
#209 ·
Hi Guys,

I have a 2001 SLK230, just recently I had MB replace all the parts that were affected by the leaking cam solenoid they even replaced the ECU, injectors, and a slew of other things under warranty at no cost which was amazing.

However before my car went into service, my radiator fan quit working, so naturally I thought It was the dreaded fan control module which it was, when I opened the old one it was pretty burned up. So I bought a new one and the Radiator fan started working fine for a few weeks. Now I am back to square one with it, mind you the fan control module was bough brand new from Autohaus.

I did however notice that the radiator fan will turn on when I have my heating set to full with EC off, but it turns on very weekly but just enough so my car doesn't over heat, with it being winter here atm this is not a big issue but I rather get it repaired sooner than later.

Does my problem sound like it could be a faulty K40 relay?

Once again I notice the radiator fan only turning on when the heating is set to full with the EC turned off, it doesn't blow its full strength like I remember it, the blower heater fan in the car works great btw.

Thank you,
Mike
 
#210 ·
The fan only starts working at a certain temperature; you're probably worrying about nothing. Does it run with the AC on?
 
#212 ·
#213 ·
no start and transmission locked in park

car will not turn over. with cover removed on k40 if I manually close relay will ignition switch is in start engine starts and runs fine, but transmission locked in park.
 
#214 · (Edited by Moderator)
jovans46 said:
car will not turn over. with cover removed on k40 if I manually close relay will ignition switch is in start engine starts and runs fine, but transmission locked in park.
Click to expand...
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#215 ·
I bought this 99slk230 from my sister who has had it parked since August. The battery is dead so I'll either have to wait to come back and charge it or tow it to my place. But the reason it was parked was while driving the car would studder, lose power (performance power and running power), and die. At first it would start back up after 15-20min. Then as time went on it would take longer. Till eventually it died and would not start back up. I've pulled the k40 and the solders look good but there is a slight crack in the board at the edge near the connections.

Unfortunately I cannot further diagnose at the moment until I have a working battery. But any help to point me in the right direction would be greatly appreciated. I just have a gut that the k40 is the problem but it looks brand new aside from the pin connectors some show significant signs of heat.



Image


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If anyone knows where to find schematics for the k40 relay, or any other component for that matter, also the specific voltages for the relays, if you would kindly post them up or a link I'd greatly appreciate it. I'd like to bench test this one before I spend money on a part that I'm not sure will fix it or not. If I knew it was the problem that would be one thing but I don't like throwing parts at a car hoping that they fix something. I like to diagnose and fix.
 
#216 ·
I've looked for the same to no avail. It is worth your time to re-flow the solder on all K40 PCB joints while you're waiting - it's free at least.

Your symptom is more consistent with the common CKP sensor failure rather than K40.

I share your sentiment - diagnose first, replace second - but neither a K40 nor CKP failure is readily diagnosed, even with great tools. Fortunately, both are relatively inexpensive components.
 
#217 ·
#218 ·
efair said:
I've looked for the same to no avail. It is worth your time to re-flow the solder on all K40 PCB joints while you're waiting - it's free at least.

Your symptom is more consistent with the common CKP sensor failure rather than K40.

I share your sentiment - diagnose first, replace second - but neither a K40 nor CKP failure is readily diagnosed, even with great tools. Fortunately, both are relatively inexpensive components.
Click to expand...
:frown:
I searched for ckp and I take it that is the crankshaft position sensor? I've always known the crankshaft position sensor to be a cps.
 
#219 ·
Crack on the board appears to be a scratch on the solder mask layer and probably happened during the dis-assembly of the case. I would not worry about it to much, it's on a large copper grounding pad and won't effect anything.

My experience with K40's is limited to only 3 but from what I have seen yours is by far way cleaner than the ones I have opened.

Follow Efairs advise and reflow all the solder joints for a peace of mind.

I would also recommend ordering a can of DeoxIT D5 spray to spray the PCBA down. D5 is a electronic contact cleaner that will eliminate and prevent corrosion.

BTW, I sprayed all my electrical connectors on the K40 and ECU with DeoxIT and let it soak in for 5min then used compressed air to blow out the residue. This stuff is amazing, pricy but worth it.
 
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