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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22736
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My mercedesc270 cdi is poorly ! She will not start , turn on

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My mercedesc270 cdi is poorly ! She will not start , turn on ignition and all that happens is a click click . She has a 6 mth old battery which is fully charged , have taken her to a local garage and was told it was the starter which has now been exchanged for a new one and the problem has not been solved , could u shed some light please,? Car is 03 plate
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
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Customer: replied 2 years ago.
Battery is fully charged . Starts from a booster pack . All the dashboard lights are working . Could it be the throttle not having information from starter electronic throttle control unit
Customer: replied 2 years ago.
Can u reply to last message , I,m doing my head in here . Nicest car I,'ve ever had if u can't help us then we're doomed
if the car will start from a booster pack then I'd say the battery may be faulty or the thick power leads are not firmly connected or have corroded connections
also check the main starter lead for a high resistance