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*Registered
2001 SLK320
Joined
4 Posts
Discussion Starter · #1 ·
Long-time lurker, first time poster! Just bought my second r170 yesterday, which unfortunately won't start today...

Upon turning the key into position 2 (the "run" position), the whole dashboard illuminates and engine cooling fan comes on at max speed. I am fairly sure I can hear the fuel pump prime. Position 3 will not engage the starter. The battery is charged btw.

In my testing I have sent 12v power direct to the starter motor which turns over fine. All the pins in the engine relay module (part no. A1705450105) appear to have the correct voltage at the respective key positions, except for the send to the starter motor, which doesn't get 12v when the key is turned to pos. 3. Am I right in assuming that putting in a used engine relay module, A1705450105, from ebay should rectify the problem?

Is it worth taking the engine relay module apart to have a look at/solder? Should I have a look at/replace the K40 while I'm at it - just seen a lot of talk about it on these forums!

Thanks Guys!
 

**Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
Joined
9,237 Posts
K40 Module, don't mess with it, just buy a brand new one from MB, which is not a fortune and usually cheaper than the Chinesium junk on various sites ;)

Then it will last another 20 years, repairs depend exactly what is wrong and are a lottery as to how long before it leaves you stranded somewhere on a dark rainy night ;)
 

*Registered
2001 SLK320
Joined
4 Posts
Discussion Starter · #5 ·
鈽 wot @Dave2302 said.

Soooooo many stories about folks trying to re-solder and ......re-solder and..... Well, success stories are few and far between.

Just buy new MB (and not ebay, etc) (y)

Thanks Leo,

But should I be buying part a1705450105 (the engine relay module) or a1705450305 (the K-40 module)
 

*Registered
2002 SLK32 (x1), 2003 SLK230 (x2)
Joined
390 Posts
Genuine MB replacement K40.

For those who are truly skilled at soldering, I have a success report, fixed ours and been working fine for many years. Reflow and cleanup any questionable solder areas AND inspect the relay contacts for pits, polishing with 2000 grit paper to new surface and check contact resistance with a meter. It will get you down the road, then order a new one and keep this for a spare if ever discontinued.

Happy top down spirited motoring, reliably.
R
 

**Premium Member '02 R170 SLK V8 5.0 & '00 SLK320
Joined
9,237 Posts
Why would you recommend changing the K-40 instead of the engine relay module?
Because ....

1) The Module on the Drivers side is the Pulse Module and does not have Engine related Relays inside it aside from the Starter Relay, which won't work when the K40 is not supplying voltage to the Motor ECU !!

2) You have the classic symptoms of K40 not supplying power to the Motor ECU.

3) I have been known to fix the odd few Mercedes.

should I be buying part a1705450105 (the engine relay module) or a1705450305 (the K-40 module)
What you should do, especially as this car is new to you (might have a wrong part fitted) is to call Mercedes Parts Dept and give them your Reg Number and they will supply you a correct and decent part, don't cheap out and buy from internet etc they seldom work for long, if at all ;)

HTH (y)
 
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