W210 K40 Relay blowing fuse

[bob6600]

Well the W210 is back together (not completely) but enough to do a test start. So I turn the key and...nothing. Well almost nothing, I have ignition lights and key turns but that's it. Checked my connections and they are all ok. Turning to fuses, the 4th fuse (7.5A) on the K40 p/n A0005400372 is blown. Annoyingly, this also powers the diagnostic socket on pin 2 so I cannot connect it to STAR. I replaced the fuse and it is fine until I try turning the ignition on and it blows straight away.

My first thoughts are near the starter motor as I had to disconnect the -ve feed as it goes through the manifold. I know it was definitely all connected but will check tomorrow. I know the K40 can also be troublesome but it seems to be this fuse. Anyone know what is causing this or what this fuse is for? It's the 4th one along, the first 7.5A.

After days of work I am gutted that it won't even turn over!

 

[Dec]

My w202 and some others similar to yours have a 10amp fuse in the 4th slot, see here...Google Image Result for http://i63.tinypic.com/2eg8uxe.jpg

Dec

 

[bob6600]

Yes I saw that on some images ad ebay. I think it depends on the part number.

 

[Joesoap17]

Try a 10A fuse if you have a dead short it will go also!!

 

[bob6600]

After retracing it all in my head last night I decided to ignore it and sleep on it. Today I checked in the very limited space where the starter is and the round wire wasn't even connected but instead was sitting on the positive terminal! I remember disconnecting it a second time but must have forgot to put it back on! After securing it and checking it isn't touching anything else, new fuse in and it cranked over nicely. Phew!

 

[Joesoap17]

sleep is the one thing that helps crack lots of problems!!
Can't count the number of times I have lain in bed and remembered the bolts I haven't tightened, pipes that weren't put back on!
That is one of the perils of DIY but even the "pro's" do it, Learnt at an early age, when my mates Renault traffic's front wheel came off after getting the front brakes done at a garage?

 

[bob6600]

Well maybe not. All was well once the starter was connected properly but today the fuse blew and now keeps blowing. Starter is fine so it's not that. I did have the top EGR cooler hose blow off (not sure how?) so wondering if water water got onto/into the M55 shut off motor as this is also on that fuse although it sits physically away from this.

 

[bob6600]

Right, this is seriously doing my head in now! I tried the following turn by turn

Disconnected starter, fuse still blows with ignition on
Removed K40 relay, still blows fuse with ignition on
Disconnected M55 inlet port shutoff motor, fuse still blows
Removed K40 board, no burnt out tracks

Now I'm not sure what else is on this circuit as there is no fusecard for these 5 fuses (damn you MB) so I am stumped for now. The fuse never blew prior to the HG being done and first blew when I forgot to connect the starter -ve cable. Once connected, it ran fine for a day and fuse was intact. Fuse blew the next day and has been blowing since

 

[grober]

OK I may be preaching to the converted here but the overload protection relay is actually a multi relay unit and each fuse is inline serving each individual power supply line switched by each of the 5/6? internal relays. Unfortunately the purpose of each fuse varies according to the engine and systems fitted so its difficult to say which each one does. Symptom would suggest that the output from the relay in question is shorted directly to earth on ignition switch on. Chances are that you have maybe disturbed some wiring during your engine repair or blown the OPR circuit board /relay somewhere.
an example of fuse assignments
f1 traction system 15A
f2 EDC engine diesel control 15A
F3 CIRCUIT 87 MOTRONIC 15A
F4 Airpump 40A
F5 FUEL PUMP 15A
F6 FANFARE HORNS 15A

 

[markmifsud]

Bob, do you have Web ETM? thats showing me that f4 is 10A. Also says Ignition Coils?

 

[grober]

A link to that ETM would be useful- or is it a subscription thing? Unfortunately since the OP's car is a diesel its unlikely the fuse in question supplies any ignition coils in this particular case------?
That's what I mean about it not being entirely clear what the function of each fuse is as it varies from model to model.

 

[toolman1954]

Web ETM 210...... Note needs Internet Explorer 5.0 and I only use chrome which is not supported

Web ETM Model 210

I rather thnk the damage was done when you tried starting the engine without the neg lead on. Do you have a wiring diagram? check all the relays that the fuse supports, seems the contacts in a relay may be fused together giving a dead short.. Are you aware of how to test a relay with a little 9 volt battery? Have you got a multimeter to test voltages? Obviously when the fuse has blown there will still be a spurious voltage on the other side of the fuse. Just work backwards from that till you find the culprit. Even a 12 volt light up prod would be handy.

Steve

 

[Ted]

If you are looking for a short circuit, remove the fuse and put a large wattage (min 21w max 55w) across the fuse holder contacts.
When a short is present, the bulb will be full brightness.
Disconnect/trace until the bulb goes out or dims.
Caution. The bulb will get hot. Don’t rest it against anything that will melt.

 

[bob6600]

Bob, do you have Web ETM? thats showing me that f4 is 10A. Also says Ignition Coils?
View attachment 76654

I tried it in IE 11 and it doesn't want to work lol. It's fuse F2 (they start numbering from the right)

I was reading some old posts last night (one was mine!) and I previously had a problem with this fuse which also stopped the duo valve working so today I will check the valve and circulation pump. I now remember that when I was bleeding the coolant system the blowers were blowing warm so hopefully I'm onto something!

 

[bob6600]

If you are looking for a short circuit, remove the fuse and put a large wattage (min 21w max 55w) across the fuse holder contacts.
When a short is present, the bulb will be full brightness.
Disconnect/trace until the bulb goes out or dims.
Caution. The bulb will get hot. Don’t rest it against anything that will melt.

Thanks I should have a bulb lying around, will give it a go if cannot find anything obvious.

I rather thnk the damage was done when you tried starting the engine without the neg lead on. Do you have a wiring diagram? check all the relays that the fuse supports, seems the contacts in a relay may be fused together giving a dead short.. Are you aware of how to test a relay with a little 9 volt battery? Have you got a multimeter to test voltages? Obviously when the fuse has blown there will still be a spurious voltage on the other side of the fuse. Just work backwards from that till you find the culprit. Even a 12 volt light up prod would be handy.

Steve

I do have access to WIS but I'm not too clever with wiring diagrams. I first thought the starter is causing the problem but if there was any short then I would imagine it would not start. I vaguely remember how to test a relay, will look it up, thanks.

 

[markmifsud]

I tried it in IE 11 and it doesn't want to work lol. It's fuse F2 (they start numbering from the right)

That just adds to the list of questions, F2 listed as traction control

 

[bob6600]

That just adds to the list of questions, F2 listed as traction control
View attachment 76657

Have a look at K40/2f2 please

 

[markmifsud]

K40/2 is not the right FuseBox

 

[grober]

Can you post up your vin number please or PM if you prefer

 

[markmifsud]

Web ETM 210...... Note needs Internet Explorer 5.0 and I only use chrome which is not supported

All you need is the web viewer for DWF files installed, then edit the js code to stop checking browser versions. works fine on my windows 7 64b PC.