Mercedes A140 starting and cooling fan problem

[Aaron Godfrey]

Hi, I am new to this site and I am looking for help as I am extremely baffled. I unplugged the 2 connectors on the ecu/maf and when I was putting everything together I tried to start the car but it would not turn over, then I realised I forgot to plug in the 2 ecu/maf connectors so I plugged them in and now it still will not turn over when I plug diagnostics in, it says no communications with the cars ecu. When you turn ignition on the cooling fan runs at high speed and does not go off until you turn ignition off. All ignition lights work but when you turn the key nothing happens. The starter motor is fine as have run a wire from positive battery terminal straight to the starter.motor and the starter motor turn the engine over but still would not start the car. The ignition switch is working fine. Any help is appreciated, Thanks in advance Aaron

 

[panason1c]

Might help if you explain what the problem was prior to unplugging the ecu/maf connectors?

 

[Aaron Godfrey]

hi sorry I unplugged it due to removing air box being to clean up the oil I spilt when I put oil in. the car ran fine before I unplugged the ecu.

 

[area51]

The ecu connectors can sometimes be a very tight fit. My guess is that one or both connectors are not fully home.

When refitting them I have found that it helps to apply gentle pressure to the back of the connector whilst pushing the retaining slider back into place.

You should see the connector being pulled into the ecu by the action of the slider.

 

[Aaron Godfrey]

hi thanks for the reply. I have unplugged them and plugged them back in a few times yhey seem to be going on properly but still nothing I know the maf is broke as it was driving like a dog but I just removed it off the air box till I get another one some is the a possibility that the ecu part of it has gone now???

 

[Auto-mobile]

You have clearly done something, check fuses and double check plugs, make sure haven't pushed a pin out one of the plugs to.

All the issues you have point towards no power/can to Ecu.

 

[Aaron Godfrey]

ok will double check tomorrow. is there a possibility I have locked the ecu or erased the memory from trying to start it when the ecu was unplugged?

 

[Auto-mobile]

No not at all, I have done that before on various mercs over the years with no adverse effects bar fault codes.

 

[panason1c]

Might be worth trying.........Remove ignition key, unplug the 2 connectors, disconnect the battery, re-connect the connectors, reconnect battery ........ try to start car.....

 

[Aaron Godfrey]

ok will try all this in a hour and get back to you. also if the k3 relay is faulty will the relay cut the bower to the ecu maf or is it just for the starter motor?? tganks

 

[Aaron Godfrey]

checked the starter plug by the battery with a volts tester and as I turn the key to start position there is no power there which tells me the starter lock out relay is broke (K3 RELAY) but would this cut the power to the ecm??

 

[area51]

hi thanks for the reply. I have unplugged them and plugged them back in a few times yhey seem to be going on properly but still nothing I know the maf is broke as it was driving like a dog but I just removed it off the air box till I get another one some is the a possibility that the ecu part of it has gone now???

I thought that the maf was within the ecu on the W168? What is it that you've removed from the airbox??

Any luck with locating the K3 relay? If your car has one then they are less than £10 or I have a spare one here you could try (dependant on your location...)

 

[Billy albert]

Fan is not getting a signal from ecu by the sound of it, if all is connected it may be a blown chip in ecu, hope not but can be repaired

 

[Aaron Godfrey]

my a140 was running roughly so took it to a garage and they said the maf are built in to the ecu so it is expensive to replace so the garage disconnected the maf/ecu from airbox as a temporary measure and since they had done that I noticed oil streaming behind the car as I drove it. so I parked it up for 6 months as had use of another car. after six months past I decided to have a go at it. the battery was flat so I put jump leads on it from my other car and it fired straight away so I thought if I clean the old oil up that is all over the manifold under airbox it would help to see were the oil is coming from so I disconnected the two plugs on the maf/ecu and cleaned the oil and I thought it would be easier if I left the airbox off while I started the car as I could see a lot more when airbox was off but as I put key in ignition and turned the key to start the car the ignition light were on but notging happened, no noices or no turning over then I realised I forgot to plug the maf/ecu in so turned ignition back off and plugged it back in and the radiators fan came on at high speed and doesn't go off until key is turned of ignition but apart from that it was still nothing it was exactly the same as when it was unplugged I have checked all fuses and they are all ok, I've done a volts test on the starter plug buy the battery whilst holding key to start position and there is no power so ran a wire from the plug to positive terminal of the battery and it tuned over but didn't start. I've plugged in diagnostics (that I have used on the car before) and it said the ecu is not responding/ communication error. think I will change k3 relay first but I dont think the relay will cut power to ecu. the car will not bump start either. really stumped. I was told if you buy a second hand ecu/maf it will not start the car as it will need programming but if I bought the ecu/maf with same part numbers along with the imobiliser receiver, imobiliser control module and key fob it will start so won't need programming. I haven't got a clue what to think/do. thanks to all for their time to read through and help it means alot. im located in South Wales, Pontypool not far from Newport. thanks Aaron.

 

[Aaron Godfrey]

area51- yes its a green relay in a box that's behind the windscreen washer fill bottle, its secured by 3 star bolts and clips on sides and bottom. when you get inside the is a ecu at top compartment, the middle has foam in it but nothing else and then at the bottom there are lods of wires and some foam, remove the foam and push wire to the side and right at the back will be 4 relays and the starter lock out relay will be the only green relay with 5 prongs.

 

[Auto-mobile]

I'm starting to think that you may need to get the Ecu tested, maybe a blow chip etc like what billy Albert said.

 

[Aaron Godfrey]

yes that would make sense but when I tried to start the car it was unplugged so no power to the ecu and when I plugged it back in the ignition was off so no power to blow a chip :/

 

[Aaron Godfrey]

I got nee k3 relay today and plugged it in and all is still the same so I got my trusty volt tester out again put the ignition on and tested power in the 2 plugs that plug in the ecu, I couldn't put the probes of tester in some of the connectors so just put them in the bigger connectors and I got three earths and 3 lives from the top plug but nothing from the bottom im guessing the power is put in the top plug to go through the ecu then cone out the bottom plug not sure though but think I have got a blown ecu/maf???

 

[Aaron Godfrey]

just letting everyone know that I have sent my ecu off to be rebuilt. will let you all know if it sorts the problem when I get it back thanks to everyone that helped.

 

[Billy albert]

Where did you send it to be diagnosed ?