W210 K40 Relay blowing fuse

[bob 6600]

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!

 

[Linuus]

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!

I had exactly the same problem in the past, turn the bad of the PCD had a burned track.

So I done a bridge bet went the pins. And checked if the relays was actuation. Then I had the starter replaced and is fixed now.. but it’s was a headache for me

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[bob 6600]

I will remove it and have a look. All was fine prior to disconnection so will check starter wires and the board. Thanks

 

[bob 6600]

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!

 

[bob 6600]

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.

 

[robparker]

Looking at the k40 relay from the front, in the back left corner there is a wire plugged in with a small (I think blue) connector. This is for the small fan for the engine ecu, we don't need it over here. Unplug it and replace the fuse.. see if that works.

 

[robparker]

In your pic, it's the small blue plug with the twisted brown and red wires

 

[bob 6600]

In your pic, it's the small blue plug with the twisted brown and red wires

Thanks Rob will try it tomorrow.

 

[LostKiwi]

In your pic, it's the small blue plug with the twisted brown and red wires

Are you sure? That looks like CANbus to me?

 

[robparker]

Yea I'm sure, that little fan gets wet and shorts and keeps blowing the fuse then you can't start, great design right there!
Might not be his problem, but worth a try

 

[bob 6600]

The car only had starting issues when the starter ground was adrift and was shorting the fuse. Since I sorted that out, car starts perfectly and the fuse stopped blowing. However, after a day's driving and the EGR cooler pipe coming adrift I thought I would run a diagnostic and there was no comms. I checked the inlet motor and it does not move. Checking the fuse and yes it's blown and keeps blowing new fuses as soon as ignition is turned on. The problem is car is limping because of the inlet motor and obviously not diag port (this fuse powers pin2 ignition feed to the port)

 

[bob 6600]

Well today I tried the ecu fan and no difference, thank you though for the suggestion @robparker

I also checked the starter and wires are ok - thankfully as the car starts fine. I then disconnected the M55 inlet port shutoff motor to see if it was the culprit and nope, it still blows the fuse. I haven't yet removed the board to check it but that will be next.

 

[bob 6600]

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

 

[Linuus]

Looks like what ever runs on that circuit is running extra load


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[bob 6600]

Looks like what ever runs on that circuit is running extra load


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I can't think why MB would leave these fuses out of the fusecard. I was reading some of my old posts last night (when I last removed the manifold) and this fuse blew then too but it was replaced and all ok. It also has the duo valve on it and possible cooling circulation pump so will be checking these today

 

[LostKiwi]

I can't think why MB would leave these fuses out of the fusecard. I was reading some of my old posts last night (when I last removed the manifold) and this fuse blew then too but it was replaced and all ok. It also has the duo valve on it and possible cooling circulation pump so will be checking these today

Cooling circulation pump has a nasty habit of seizing....

 

[Linuus]

I’ve been dealing with some weird behaviour on my S210. Starting with the cluster... and the lost is power a couple of weeks ago..... and with a new starter 3 months ago. And some fuses...


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[bob 6600]

I’ve been dealing with some weird behaviour on my S210. Starting with the cluster... and the lost is power a couple of weeks ago..... and with a new starter 3 months ago. And some fuses...


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Did you sort them issues out?

 

[Uncle Benz]

Hmm. I'd be looking thoroughly to check in case you have trapped a wire somewhere. Maybe pinched between the inlet manifold and something else you have bolted up.

Do you have electric egr valve or vacuum one?

 

[bob 6600]

Hmm. I'd be looking thoroughly to check in case you have trapped a wire somewhere. Maybe pinched between the inlet manifold and something else you have bolted up.

Do you have electric egr valve or vacuum one?

Vacuum but I have finally solved the problem I think!

I disconnected the duo valve, fuse still blows
I disconnected the circulation pump, fuse still blows
M55 disconnected again, fuse still blows

Then after a lot of head scratching I thought I'd check again. I remember that the car was fine for a day and then I had a loss of water. The pipe on the top of the EGR cooler blew off, mainly because the clip was not on the pipe but just on the hose (my fault). So I checked everything around this area again and there is a connector that plugs into the top of the gearbox (or back of the engine). Connector removed, sprayed with contact cleaner, blown with air and reconnected. FUSE DOESN'T BLOW! I managed to connect STAR to it and cleared all faults. i have attached pics below of the connector and the possible fault (which I couldn't read at the time).

Thank you again for all the replies and help, I hope this thread will help someone in the future.

but I have finally solved the problem I think!

I disconnected the duo valve, fuse still blows
I disconnected the circulation pump, fuse still blows
M55 disconnected again, fuse still blows

Then after a lot of head scratching I thought I'd check again. I remember that the car was fine for a day and then I had a loss of water. The pipe on the top of the EGR cooler blew off, mainly because the clip was not on the pipe but just on the hose (my fault). So I checked everything around this area again and there is a connector that plugs into the top of the gearbox (or back of the engine). Connector removed, sprayed with contact cleaner, blown with air and reconnected. FUSE DOESN'T BLOW! I managed to connect STAR to it and cleared all faults. i have attached pics below of the connector and the possible fault (which I couldn't read at the time).

Thank you again for all the replies and help, I hope this thread will help someone in the future.