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350matt
350matt, Engineer - BEng Hons
Category: Saab
Satisfied Customers: 20605
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Starting Problem: Sometimes car fails to start. The key

Customer Question

Starting Problem: Sometimes car fails to start. The key turns in the ignition, but you hear nothing. The battery, starter, and alternator all check out; battery is fully charged. The car will not start in Park or Neutral. You don't need your foot on the
brake to start this car. You come back in an hour or two without doing anything, and the car starts.
Submitted: 1 year ago.
Category: Saab
Expert:  350matt replied 1 year ago.

Hello

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 preventingthe starter from being enabled - however if the dash / ignition lights are onthen this usually means that its off

If this is all OK then its possible the car needs a new starter motor

Expert:  350matt replied 1 year ago.

Hi

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