K40 relay module

bazzle · 11-04-2006

Early SLKs suffered from soldered joint failures on the K40 pcb. This mainly affects smooth op and fuel pump.

I have just repaired mine.

K40 Relay - Right hand drive

LHD opposite

Remove neg batt term
Remove computer lid
Unclip holding tang and lift up module
Pull off connectors
Open case of module
Inspect soldered joints for cracks, overheating, dry joint etc
An eyeglass may help (top left hand group of three)
Remove old solder and resolder with new
Replace module
Push on connectors
Remove and replace 40A fuse to wipe the contacts.
Replacelid
Replace neg batt terminal.
Start car

Redo radio code if required.

more: http://www.benzworld.org/forums/r170...ssociated.html

Bazzle

bazzle · 11-04-2006

More:

Bazzle

DesignoSLK · 11-04-2006

Yeah...it's a keeper. The post that is.

Thanks Bazzle!

**etyu** · 11-04-2006

WOW! Even though I'm not a R170 owner, I like to read the how-to stuff just for general knowledge. Thanks Bazzle.

mtiede · 11-05-2006

So was there a cold solder joint there? I don't see one. Or was the picture totally to show how to get to it?

bazzle · 11-14-2006

Quote:

Originally Posted by mtiede

So was there a cold solder joint there? I don't see one. Or was the picture totally to show how to get to it?

Just for you Mtiede

Bazzle

**SLKman** · 11-14-2006

More good info from Bazzle!!!

Hope I never have to do this. Yikes!

SLKman

DesignoSLK · 11-14-2006

Quote:

Originally Posted by SLKman

More good info from Bazzle!!!

Hope I never have to do this. Yikes!

SLKman

For some its fun! The best part of the troubleshooting procedure. For bench technicians, soldering is like...landing for pilots. Oh wait...I get to do both...woohoo!!

slk230r170 · 11-29-2006

Quote:

Originally Posted by bazzle

Just for you Mtiede

Bazzle

Wow! The Germans are sloppy with their soldering.

mtiede · 11-29-2006

Quote:

Originally Posted by bazzle

Just for you Mtiede

Bazzle

Thanks for the close up. Looks bad to me

Reminds me of the time I built my first TV. It took me 2 weeks to solder all the pieces on the circuit boards and 2 weeks to find out what was wrong

Turned out they gave me a wrong part and smoke and sparks came out of a resistor when I turned it on. After I got that figured out, then it took me a while to find a coil with a broken wire. After than it ran fine for about 10 years.

But I did my fair share of soldering and looking for those cold joints.

WeBKompressor · 10-12-2007

Hey Bazzle thanks for the post.
I had trouble starting my 2000 SLK 230 yesterday. When I turned the key to start, I got all the idiot lights and the radiator cooling fan was running in high speed. The engine was warm but not hot. The car did not crank the starting motor at all. I checked and it did not set the check engine lightl. A couple hours later I tryed to start the car and it started right up normally. I thought that the problem might be in the ignition switch or the starting motor/soleniod.
I found your post and decided that I better check it to see if that was the problem. Did you figure out what the cold solder joint controlled?
I took pictures of mine and they look identical to the pics that you posted. SO this problem is not unique to your car. If that is not the problem I will pull the starter/soleniod and then check it. There was no noise except for the radiator fan when I tryed to start it.

uncleroman5113 · 10-24-2007

My 1999 SLK230 Has Had A Rough Idle For A WHILE Now, More So In Reverse. Dealers Have Said It Was JUST A Vacuum Leak And Could Never Narrow It Down/Too Many Vacuum Lines. Car Has Also Died Out A Few Times And Wouldn't Even Crank Over After It Dies Out. The Car Failed Emissions Test Last Month. The Codes Showed A Throttle Position Switch Learned Open/Replaced That No Luck. A Fuel Pump Circuit High and Secondary Air Valve Code, And Many Other Pending Codes. I Don't Trust Any Of The Local BMW/Mercedes Dealers In My Area. They've Lied And Taken Me To The Bank Before. I Usually Fix My Own Cars But This One Stumped Me. I Didn't Want To Throw Parts At It. Today I Took It To My Local Private Shop I Know And They Said It's Probably The K40 Relay. Just Like The Post Said. I'll See If It Works.

texan151 · 12-11-2007

Happy Holidays everyone!

If your SLK230 is over 5 years old, it would be WELL worth the $170.00 US to just replace the relay unit as a preventive measure. The part is not that expensive and it's a cake walk to change out. No one likes to be stranded miles away from home! PLUS, it may take your dealer time to order one. You will be down for that long. I lucked out and got the LAST ONE my dealer had!

REMEMBER: A smart one learns their own lessons, a wise one learns lessons through the lessons of others, and not-so-smart one NEVER learn any lessons...

'Tis the season to be a "wise one", isn't it? Hehe

**alroumi** · 12-11-2007

Thanks Bazzle I like DIY's.

JOSHM · 12-23-2007

Thanks for sharing your knowledge Bazzle. Also a big thanks for taking the time to document with pictures.

jbfajkow@comcast.net · 03-08-2008

My 1998 slk230 just started symptoms of k40 relay issues. The dash lights come on and when I press the throttle, the engine does not respond although it is still running. Then, the dash lights go out and everything is back to normal. Just had the Benz dealer diagnose and they said it is a bad k40 relay. I checked the k40 relay board described in previous posts, and the soder points are clean and solid. Is the actual k40 relay on the other side of the engine compartment(drivers side)? The sealer also had "discs" listed under parts. Not sure what that is. Anyone have any knowledge of replacing the k40 relay itself, and what "discs" are in relation to the k40?

jbfajkow@comcast.net · 03-08-2008

Just searched the net for a k40 relay for my 98 slk230. I found what appears to be a k40 relay, but not the k40 relay module described in previous posts. Both part suppliers said it is located "right front under hood", but I don't see anything that looks like the picture on their site. Does anyone know anything about the k40 relay itself and where it is located? Or do I need to just be concerned about replacing the k40 relay module described in the previous posts?
http://www.autopartswarehouse.com/se...294967269+5866

apf · 07-12-2008

Does any one have the diagram of the K40 realy board? I need to find out which realy is feeding the fuel pump to install an additional relay to cut it off!
Thanks

forcefedboost · 07-28-2008

Does anyone know if the K40 controlls Spark, Starter or coil packs?

mr.machine · 1 Week Ago

I have found that this relay board is responsible for 2 failures for my mercedes

1. Check engine light error codes -

p1235, p1236, p1420, p1525 (Rightmost circle in attached image)

2. Failure to crank - intermittently (Center circle in attached image)

I am including the close up from another post showing the bad soldering points. Make sure that you solder all 3

11-04-2006	#4 (permalink)
etyu Founding Member #2 / Ambassador Of Good Will Join Date: Jun 2006 Location: Orange County, CA Vehicle: 2008 SLK 55 Posts: 4,941 Country: Thanks: 331 Thanked 216 Times in 116 Posts	WOW! Even though I'm not a R170 owner, I like to read the how-to stuff just for general knowledge. Thanks Bazzle. __________________ *Eddy* To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Pewter/Beige, PIII package, Airscarf, Hands-Free Communication System, Lighting package Designo Black Leather Cover on e-brake handle, ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Bill T), SmartTop v1.0, Kleyman 3BFM (NoRegret Custom), Green Air Filters, *Mod. R170 ant.* EuroClear sidemarkers w/PIAA PlasmaIon lamps, chromed front & rear turn indicator lamps, PIAA SuperPlasmaGTX front parking lamps, HyperWhite license plate lamps ( To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. Scott), bilateral rear fog lamps enabled.

11-14-2006	#7 (permalink)
SLKman Founding Member Join Date: Jun 2006 Location: Houston Texas Vehicle: 2000 Copper Designo Sport Posts: 1,020 Country: Thanks: 230 Thanked 61 Times in 31 Posts	More good info from Bazzle!!! Hope I never have to do this. Yikes! SLKman __________________ To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. 2000 SLK230 copper Designo Sport To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts. So many come here FOR help but are not willing TO help? C'mon people...Help the site survive...Become a Supporting Member or just Donate $5, $10 or whatever you can! Your SLK will go faster, get better gas mileage, never get dusty or dirty.... Well,... maybe not, but you WILL feel good you helped the site! To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.

12-11-2007	#14 (permalink)
alroumi Moderator Join Date: Jun 2006 Location: Kuwait City, Kuwait Vehicle: 2006 Kleemann Designo Mocha Black SLK55 AMG Other Toys: 2007 Ebony Jaguar XKR Coupe' and 06 Black Cayenne S Posts: 6,084 Country: Thanks: 248 Thanked 189 Times in 112 Posts	Thanks Bazzle I like DIY's. __________________ 06 Kleemann Designo Mocha Black SLK55 AMG 06 Porsche Cayenne S 07 Jaguar XKR Coupe' I use the Torque and keep the HP for my Steak Sauce!

11-04-2006	#3 (permalink)
DesignoSLK Elite SLK World Member Join Date: Sep 2006 Location: Kaiserslautern, Germany Vehicle: 2000 Designo SLK230 Posts: 1,635 Country: Thanks: 84 Thanked 17 Times in 12 Posts	Yeah...it's a keeper. The post that is. Thanks Bazzle!

11-05-2006	#5 (permalink)
mtiede Founding Member #7 Join Date: Jun 2006 Location: Western New York Vehicle: 2006 SLK 350 Posts: 1,419 Thanks: 71 Thanked 40 Times in 30 Posts	So was there a cold solder joint there? I don't see one. Or was the picture totally to show how to get to it?

10-12-2007	#11 (permalink)
WeBKompressor SLK World Junior Member Join Date: Sep 2007 Posts: 2 Country: Thanks: 0 Thanked 0 Times in 0 Posts	Hey Bazzle thanks for the post. I had trouble starting my 2000 SLK 230 yesterday. When I turned the key to start, I got all the idiot lights and the radiator cooling fan was running in high speed. The engine was warm but not hot. The car did not crank the starting motor at all. I checked and it did not set the check engine lightl. A couple hours later I tryed to start the car and it started right up normally. I thought that the problem might be in the ignition switch or the starting motor/soleniod. I found your post and decided that I better check it to see if that was the problem. Did you figure out what the cold solder joint controlled? I took pictures of mine and they look identical to the pics that you posted. SO this problem is not unique to your car. If that is not the problem I will pull the starter/soleniod and then check it. There was no noise except for the radiator fan when I tryed to start it.

10-24-2007	#12 (permalink)
uncleroman5113 SLK World Junior Member Join Date: Oct 2007 Location: Burbank, Illinois Vehicle: 99 Slk230 Sport Posts: 1 Country: Thanks: 0 Thanked 0 Times in 0 Posts	My 1999 SLK230 Has Had A Rough Idle For A WHILE Now, More So In Reverse. Dealers Have Said It Was JUST A Vacuum Leak And Could Never Narrow It Down/Too Many Vacuum Lines. Car Has Also Died Out A Few Times And Wouldn't Even Crank Over After It Dies Out. The Car Failed Emissions Test Last Month. The Codes Showed A Throttle Position Switch Learned Open/Replaced That No Luck. A Fuel Pump Circuit High and Secondary Air Valve Code, And Many Other Pending Codes. I Don't Trust Any Of The Local BMW/Mercedes Dealers In My Area. They've Lied And Taken Me To The Bank Before. I Usually Fix My Own Cars But This One Stumped Me. I Didn't Want To Throw Parts At It. Today I Took It To My Local Private Shop I Know And They Said It's Probably The K40 Relay. Just Like The Post Said. I'll See If It Works.

12-11-2007	#13 (permalink)
texan151 SLK World Junior Member Join Date: Dec 2007 Posts: 1 Country: Thanks: 0 Thanked 0 Times in 0 Posts	Happy Holidays everyone! If your SLK230 is over 5 years old, it would be WELL worth the $170.00 US to just replace the relay unit as a preventive measure. The part is not that expensive and it's a cake walk to change out. No one likes to be stranded miles away from home! PLUS, it may take your dealer time to order one. You will be down for that long. I lucked out and got the LAST ONE my dealer had! REMEMBER: A smart one learns their own lessons, a wise one learns lessons through the lessons of others, and not-so-smart one NEVER learn any lessons... 'Tis the season to be a "wise one", isn't it? Hehe

12-23-2007	#15 (permalink)
JOSHM SLK World Junior Member Join Date: Dec 2007 Posts: 1 Country: Thanks: 0 Thanked 0 Times in 0 Posts	Thanks for sharing your knowledge Bazzle. Also a big thanks for taking the time to document with pictures.

03-08-2008	#16 (permalink)
jbfajkow@comcast.net SLK World Junior Member Join Date: Mar 2008 Posts: 2 Country: Thanks: 0 Thanked 0 Times in 0 Posts	My 1998 slk230 just started symptoms of k40 relay issues. The dash lights come on and when I press the throttle, the engine does not respond although it is still running. Then, the dash lights go out and everything is back to normal. Just had the Benz dealer diagnose and they said it is a bad k40 relay. I checked the k40 relay board described in previous posts, and the soder points are clean and solid. Is the actual k40 relay on the other side of the engine compartment(drivers side)? The sealer also had "discs" listed under parts. Not sure what that is. Anyone have any knowledge of replacing the k40 relay itself, and what "discs" are in relation to the k40?

07-12-2008	#18 (permalink)
apf SLK World Junior Member Join Date: Jul 2008 Posts: 1 Country: Thanks: 0 Thanked 0 Times in 0 Posts	Does any one have the diagram of the K40 realy board? I need to find out which realy is feeding the fuel pump to install an additional relay to cut it off! Thanks

07-28-2008	#19 (permalink)
forcefedboost SLK World Junior Member Join Date: Jul 2008 Location: LongIsland NY, USA Vehicle: 1999 SLK 230K Sport Posts: 4 Country: Thanks: 0 Thanked 0 Times in 0 Posts	Does anyone know if the K40 controlls Spark, Starter or coil packs?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)