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Matt, Engineer
Category: BMW
Satisfied Customers: 21975
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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04 BMW 330xi Won' t crank

Customer Question

04 BMW 330xi Won' t crank
Submitted: 11 months ago.
Category: BMW
Expert:  Matt replied 11 months ago.


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 11 months ago.
having trouble. changed starter, new battery, new ignition. checked trans position switch good. noticed that red blue wire on ignition switch not live and should be. don.t know where fed from.
Expert:  Matt replied 11 months ago.


if the starter switch / ignition isn't being fed then its very likely to be an issue with the security system not allowing a start

I'd say the next step is to get the car to a dealership and have the key re-coded to match the car

sorry its not a more DIY answer but thats often the case with security systems

Customer: replied 11 months ago.
You got any clue where the red blue wire on ignition harness fed from that would really help because I tested ews and it was good and that wire feeds the crank circuit.
Expert:  Matt replied 11 months ago.

Sorry I don't have the wiring diagram for that model

I'll opt out to see if someone else on here can help