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Matt, Engineer
Category: Mercedes
Satisfied Customers: 21995
Experience:  Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
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C280: I have a 95 c280 that won't crank. It has full power,

Customer Question

I have a 95 c280 that won't crank. It has full power, all lights, stereo, heater, ect. works. It doesn't do anything when the key is turned to the crank position and the CEL does not come on when the key is first turned to the on position. Also, there is no communication between the OBD2 and a reader--just an error message.
Submitted: 2 years ago.
Category: Mercedes
Expert:  Matt replied 2 years ago.
Hello ***** and I'll try to help you with this
If the car's not cranking then first check it can turned over by hand so double checking for any mechanical issues
If OK then check that the main battery cables are on tight and the terminals are clean and bright. Do the same for the engine / gearbox earth strap.
Then follow the main positive lead back to the engine and down to the starter motor, and check the connection at this end as well.
There should also be a small wire to the motor which should have 12V when you're turning the ignition switch to crank. If the 12V isn't there, check back along this wire for damage to the insulation or corroded connections
This 12V feed comes directly from the ignition switch so this may be faulty and need replacing
Check the resistance of the main positive lead that runs down to the motor as anything more than a few ohms and it should be replaced
Don't forget to try a jump start from another car / battery as its possible the battery is poor, if you have a voltmeter a healthy battery should read 12.7+V
also try substituting the battery for another as I've known a very flat battery to drag down the system voltage too far even with jump cables
one other thing to consider is that the immobiliser is faulty and preventing the starter from being enabled - however if the dash / ignition lights are on then this usually means that its off
If this is all OK then its possible the car needs a new starter motor
Customer: replied 2 years ago.
On the C280 the wire that goes to the starter solenoid (purple) comes from the ECU, not the ignition switch. I am not getting power to the starter, but I do get power out of the crank position of the ignition switch. I don't know if you noticed in my description that the CEL and OBD2 no longer work, because you didn't comment on that. I also mentioned that the battery is fully charged. Your comments appear to be a pre-typed catch all for cars that don't crank. If you would please take my problem on as a unique situation, it would be very much appreciated. I have a mechanical background and need someone that specializes in Mercedes, as this problem is unusual to me. Thanks Matt
Expert:  Matt replied 2 years ago.
thanks for the extra information
in that case the next step should be to confirm that the ECU is getting 12volts
I'd use a voltmeter on the ECU fuse to confirm if you 're getting 12V or not and if you are note then check to see if the ECU power relay is clicking in and trace the circuit back to try and locate any wiring breaks between the power supply in the fusebox and the ECU plug ( the ECU is located under the hood on the passenger side)