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My 2004 Mercury Sable LS randomly does not start. I turn the key and nothing happens. I have called AAA twice to jump the battery and they tested the system twice. The results are that the battery has lots of juice, the starter tests fine and so does the alternator. It started fine for me an hour ago but when I leave work it will be a coin flip whether it will start. Is one of the pieces parts going bad? How do I solve the mystery?

  • I have to many questions to be able to post an actual answer. So maybe if you can edit your post with these details we can help you get to the cause. When your car starts, does it do it easily? In other words, does it crank slow or sound difficult when it does start? How are the cables and connections? Corrosion or damaged cables? – CharlieRB Nov 7 '16 at 22:20
  • Have you tried putting the shifter in neutral and see if it starts? This could isolate it to a safety switch fault. – mikes Nov 8 '16 at 0:51
  • It could be an intermittently bad starter, ignition switch, or solenoid. Putting it into neutral sounds like a good idea. You can get some useful information if you get a voltage meter that plugs into your cigarette lighter and plug it in when you try to start the car. They sell them at autoparts stores for about ten bucks. You might not want to leave it in the lighter in case the lighter circuit is always on. It would run down your batt. It should read 12.7 to 12.8 Volts and then drop a bit when you try to start the car. If it doesn't drop it's probably the switch or the solenoid. – Eric Nov 8 '16 at 3:21
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This past weekend, I tried to return a 3 month old battery to my local auto parts store. After charging for 2 days, it showed 11.9 volts. It should have been ~12.8 volts. It's factory rating is 440 CCA. Of course, at 11.9v it could not start the car.

Do you know what they told me when they tested it? IT "PASSED". It tested at 11.9v (no load) and 170 CCA of 440 CCA. Are you kidding me, that's a pass by their standards??! They ended up replacing the battery.

My point is, just because they said it passed does not mean it has enough juice to start YOUR car. This seems especially probable, gathering from what you said, that after they jumped it, it started fine.

Do you have/recall the test results of the battery?

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  • The battery might be fine, but the charging system isn't charging it correctly or you could have a parasitic drain that's draining it when it sits. The real test of the battery would be if it comes up to 12.8 volts when it's on a charger. – Eric Nov 8 '16 at 3:16
  • Yup, only one way to find out. Batteries go up regularly, alternators and shorts "shouldn't" be as common. Of course, for every person that says they had to replace their alternator every 2 years; there's probably 5 cars that go their whole lifespan with no alternator problems. FWIW. – justinm410 Nov 8 '16 at 14:51
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I am going to assume AAA tested the system with a battery load tester and tested the starter by starting it a few times while they were there.

Possible problems to look into

  • does your alternator give enough power? Get a volt meter and when the car is running measure the voltage between the positive and negative terminals of the battery it should be 13.5 minimum and no more than about 14.75 if it is lower it may be the alternator going out.
  • I am going to assume all the other electronics work ok but when trying to crank does the whole car go dead? this can be a sign of a loose connection. Either way you should check your battery cables at both ends for fraying or loose connections. you should also check the cable going to your starter
  • try smacking the starter with a wrench and see if it starts this could be a sign of bad or gummed up brushes. Usually you can hear the starter click the gear in place but no cranking sometimes no depending on how it is wired internally.
  • does the starter make some rapid fire clicking? If so then check connections and battery charge.
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Occasionally wont start. Battery fully charged. Dash lights on- Maybe the gear stick isn't locked properly into "Park". Try moving gear stick and/or try starting it in "Neutral". Good luck John.

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  • Hey John, Welcome to the Mechanics Stack Exchange! This answer doesn't provide a clear solution or details on troubleshooting, and would be better suited for a comment. Could you try and clear up your answer to provide some better information? – H. Daun Oct 19 at 4:32

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