intermittent Fault- turn key instrument panel lights up but no turning over of the engine just a click sound. This fault progressed to when turning the key it would stay in the start position with the engine turning over but not starting or starting and then stopping after a few seconds. Key needed to be turned back manually if it didnt start to stop the starter motor..

Hi after reading several threads I noted that there was an issue with dry solder joints on the circuit board of the ECU or RCU -relay control unit situated beside the battery under the black lid. I located and removed the unit and took it to a TV service centre to test the board and they found four dry joints- excellent.
Replaced board- still not starting and key remains in start position with starter motor turning over. GRRRRR!!
Any next step suggestions gratefully received

 

Did your 'tech' check the relay contacts? Burnt or dirty contacts have resulted in quite a few non-start issues before, I believe. Good luck!


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The failure in the RCM most often takes the form of no output to the ECU. This means the car seems to power up, but the starter will not engage.
If you leave the key at "ON" for about 45 seconds, the engine fan will warp up to high speed. This is a clear sign you have no output from the RCM to the ECU.

But you are saying that the starter is now engaging and the car still won't start. The only failure on the RCM that can cause this, is a failure of the fuel pump relay - that does happen, but it's rare.
YOu should hear the fuel pump run for a few seconds when you turn the key to "ON". You can verify you have fuel pressure with a cheap fuel pressure test kit ($30-60).

It is common for cars to quit running (but the starter engages) with a bad Crank Position Sensor. USUALLY, they fail at high temps, letting the car sit and cool will usually mean the car will start and run until it gets hot again. Perhaps your crank sensor IS bad, but with a cold engine, I'd almost doubt it.

YOu need ignition and fuel and air for the car to start. Air is the easy part, what is questionable is if you have ignition and fuel.

 

Well described !!!

 

Thanks if it faults again will check

 

hi
just one more question. The relay marked Air Pump- what does it operate?

 

It will, you can bet on it.

What I would do (and what most of us have done):

1) Order a new RCM, they are not expensive, Keep it in the trunk as a spare - they fail rather often.
2) Order two new Crank Sensors. Replace yours. Keep the other new one in the trunk - they fail rather often.

The source for the RCM is not critical, but where you source the Crank Sensor IS critical. I like GermanAutoSupply.com; many use FCPEuro.
DO NOT search "Crossfire", search "2003 Mercedes SLK320" and grab the BOSCH part only.

 

Many thanks Pizzaguy for the great advice will start filling my trunk/boot up.

 

Thanks Pizzaguy.
Thought I had fixed it and it started every day. Then when I went to actually drive it after it had been idling it stopped as I reversed out of my garage! Now back to not starting just turning over and fires once then stops.
I will order a RCM as you say.
Where is the crank position sensor located ? Just want to make sure I get the right one.
I think lack of use has led to this issue.

regards

 

Info on the Crankshaft Position Sensor click: CPS install

 

I remember driving a '77 straight-6 250 CI Chevy Nova as a kid on about a 13 hour/700 mile trip. It started having problems and loss of power up hills and I limped up an exit in the middle of nowhere on I-80 across PA and found an auto repair place at like 1AM. I parked there in the lot and slept in the back bench seat until the next day. I knew I had air, I knew I had spark as I tested for that... Next day the place opens and I wake up from the back seat out from under my blanket (ALWAYS KEPT A BLANKET IN ANY CAR ON ANY LONG TRIP) and the mechanic I walked up to said the same thing... AIR, SPARK, FUEL. He said ya got spark and air but no fuel. He found a tiny clogged fuel filter in the old 2 barrel carb I think it was in that thing. I think he charged me $5 to find the problem and change out that tiny filter. That was just good people taking care of good people I say. Lotsa good people here on this forum too.

Pizza and Graphite are right... Buy a new RCM and plug that in and see if the problem is fixed. If not, you are gonna want to keep a new RCM in the car all the time anyway as most do. I also keep a spare crankshaft position sensor and a spare camshaft position sensor around. I'd put those 2 in the in the car for any long trip to have them on hand in case of a breakdown where I don't have all my tools and it could take a shop a few days to get one in if that's the problem.

 

Hi helpers
So here is the update.
Pizzaguy you will be pleased that I have had the Relay Control module resoldered- got the board checked by a TV service team here in New Zealand- found faulty solder joints- Tick
Replaced the CPS bought for $80 NZ from super cheap. Same part $170 at Mercedes-Tick
Turned key started or should I say fired and ran for a second or two then died. Now same fault turn key and let go and the key stays in crank position with car turning over. Manually turn key back to stop cranking.
I can smell fuel so I think pump must be supplying fuel.
GRRRRR That what I get for not using it very much lol

Any ideas?