W203 Fuse Box Unit / Relay Issue.

[jeffcoo]

Hi,

Initially a non starter issue I thought Immediatly Battery, so bought a new 019 good make Battery, still not cranking. ( but dash lights come on )

Still not starting. hmm.

I remember a few months back I had a similar issue with her not starting changed Fuse 31, and it cranked fine.

This week, not starting again, and paid a mechanic 200! to tell me the same, put his diagnostics on the car, and 2 hours later, he couldnt tell me anything.

I have since been trying to diagnose the issue, but am currently stuck.

I have checked the usual 'suspect' Fuses on the W203, ( numbers 31, 52 and 57 ) all seem ok.

The mechanic checked the Relays, which seemed ok. He told me it was 'Ignition related' and quoted me another few hundred, hilarious!

I have owned a few mercs over 20 years and something didnt feel right in relation to the ignition problem diagnosed by the mechanic.

I was checking the Fuses in the Drivers side Fuse Unit, ( i think where number 31 is located ) I was moving the fuses, and pusing them in and wiggling them and turned the key, and she started! ( however she isnt starting again )
obviously this is illiminating the Ignition fault, right?

also the central locking isnt working. Which seems odd.

am i wrong to think it could be the Fuse Unit Related ? ( drivers ).
Has anyone come across this before, perhaps the wiring into Fuse 31.


Another w203 i had a few years back had a similar issue and it too was 31 Related. ( i upped the Fuse to 40 from memory )
However, instinct is shouting at me, it must be wiring, or the Fuse Unit itself,

If anyone has had a similar issue i would be grateful to hear.

I really think the mechanic isnt right about the ignition,however, an open mind is best.

Thanks Jeff

 

[television]

Is the dash all lighting up when you turn the key ??

 

[jeffcoo]

hi Yes the dash lights up, and I hear the usual clicking when attempting to start ( sounds like a relay 'talking' )
the dash currently has ' Restrain System Visit Workshop' SRS displayed.

 

[turbopete]

so you get the buzz unlocking the car, everything works as expected, but just a 'click' when trying to crank? if my way of reading it is correct, id start by checking the earth points and then check that the starter is ok. try switching on the headlights if near a wall etc, turn the key to start and see if the headlights stay bright or go dimmer

 

[television]

hi Yes the dash lights up, and I hear the usual clicking when attempting to start ( sounds like a relay 'talking' )
the dash currently has ' Restrain System Visit Workshop' SRS displayed.

OK you need to work back from the starter. There should be 12 volts always on the large fat wire, the smaller wire should have 12 volt when the car is turned to start. If 12 volt there the starter has failed, No 12v then go to the starter relay and check in the socket that 12 volts is there when turning to start.

 

[jeffcoo]

I havnt checked the earth points yet, but starter motor is fine

the lights when switched on seem ok, and do not dim,

this is with the light switched on. When i turn the Key to final cranking position, this doesnt seem to engage the lights . the only thing that is currently happening when the key is turned to crank is i hear a clicking noise ( which i interpret as a relay ) although it could be something else, and also after about 20 seconds the main fan comes on. Fast, and very loud.

 

[turbopete]

i was referring to the headlights being switched on, not the dash/interior lights.

the relay clicking noise you refer to would certainly point me in the direction of an earth fault or a starter issue. if you have some jump leads you could try connecting 1 lead between the engine and the other end on an earthing point on the body, just to test that theory

 

[television]

The fan coming on tells me that the problems are in the K40 engine ECU, either a poor fitting fuse, or fuse blown or bad connection within the ECU. The fan is held off by the ECU having the correct voltages.

 

[turbopete]

The fan coming on tells me that the problems are in the K40 engine ECU, either a poor fitting fuse, or fuse blown or bad connection within the ECU. The fan is held off by the ECU having the correct voltages.

would a starter issue or earth issue not cause a temporary drop in voltage sufficient to trigger the fan? or would the voltage have to be down for longer than a couple of seconds?

 

[television]

would a starter issue or earth issue not cause a temporary drop in voltage sufficient to trigger the fan? or would the voltage have to be down for longer than a couple of seconds?

No, if the fan comes on at full speed, then not a grounding problem.

 

[jeffcoo]

i was referring to the headlights being switched on, not the dash/interior lights.

the relay clicking noise you refer to would certainly point me in the direction of an earth fault or a starter issue. if you have some jump leads you could try connecting 1 lead between the engine and the other end on an earthing point on the body, just to test that theory

sorry to confuse, the headlights go on and do not Dim

 

[jeffcoo]

The fan coming on tells me that the problems are in the K40 engine ECU, either a poor fitting fuse, or fuse blown or bad connection within the ECU. The fan is held off by the ECU having the correct voltages.

Hi,

where is the K4 located is this a relay?

I have limitations and to be honest I think i need to call an independent out,
I am comfortable with Relays and locating them and changing them, if its moderate to do I think I can handle it.

 

[television]

The K 40 is the engine ECU and associated parts like starter relays and fuses.

I cannot give the exact location till later in the day and fuse numbers.

 

[television]

Your car, petrol or diesel please or the first 6 VIN numbers like 203---

 

[jeffcoo]

hi its diesel W203 / 2002 plate estate

with Fuse board in the boot / drivers side cabin / and left hand side under bonnet


thanks

 

[jeffcoo]

The fan coming on tells me that the problems are in the K40 engine ECU, either a poor fitting fuse, or fuse blown or bad connection within the ECU. The fan is held off by the ECU having the correct voltages.

just an update incase it helps:
I put 2 new batteries in the Key Fob, as the red light on the Fob wasn't coming on as usual, inserted the Key and she cranked and sounded lovely........
( i realise that the Key needing new batteries could just be a coincidence )

weirdly today the wipers are now not coming on.

Although she started and cranked that time, I have since tried to crank her and nothing.....

I wonder what this means that she will start in such a random fashion, then may not start again for days. And now the Wiper issue....

does this mean anything - Is this a usual or a typical fault that is SAM , Relay or K40 Related?

Cheers

Jeff

 

[turbopete]

could also be a key or EIS issue

 

[mattuk]

sound like an issue with front SAM unit.

Open fuses cover under the boniet and check all relays. plug out one by one and check resistance in Ohms with a multimeter. don't forget about the little relay under the wires.

 

[television]

The batteries in the key fob only do the locking, so that one is now clear, with the key in the car, the car energizes the key fob, the key turns so EIS switch all good. this now leaves the starting fault so ECU maybe SAM it may need STAR. I will now check on the fuses that can affect this and post back again.

 

[umblecumbuz]

Have just changed a front SAM on a friends W203 cdi 220 because of similar issues. Wipers inop, plus one headlight - although for a short while both headlights came on with ignition and would not turn off. Car would sometimes crank and start, other times not, but dash lit up like a fairy tree.
Changing the front SAM fixed all the problems.

What a learning curve these W203's are!