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The car is a 2007 Mazda6 3L which I parked overnight and won't turn over in the morning anymore. I did some preliminary diagnostic and ruled out some possibilities:

  • The battery is full, 12.4 V.
  • The starter is good, so is the connection from the load side of the relay to the starter. I was able to jump the starter powering the relay.
  • The ignition switch is good, I hear a click even with the relay removed.

When the starter is jump started, the engine shakes but it still doesn't start, so I'm think maybe the fuel injection system is locked by safety feature. I'm thinking the neutral safety switch, but had no luck starting in other gears as well. Is there anything else I should check for?

Edit: There was a u0100 code that popped up, has to do with lost communication with the ECU. Not sure if related.

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    Welcome to Motor Vehicle Maintenance & Repair! When you state "not even a crank" do you mean the engine doesn't rotate at all or are you saying it will rotate but not fire?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jun 9, 2020 at 22:28
  • The starter won't crank, so the engine won't move at all. I can only make the starter move when I jump start it.
    – PeaBrane
    Commented Jun 9, 2020 at 22:30
  • How do you know the starter is good? Just because it will turn doesn't mean it's good.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jun 9, 2020 at 22:34
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    Locate your security/immobilizer light displayed on instrument cluster. With key turned to the ON (don't crank) position does it flash, come on and cut out or stay solid?
    – narkeleptk
    Commented Jun 9, 2020 at 23:21
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    Slow flashing with key in off is normal operation. If its flashing when key is ON then your immobilizer is active and there will be no fuel, spark or crank on this mazda. Either your key needs to be reprogrammed, your receiver is gone bad or your immobilizer (in instrument cluster) is not communicating with pcm to verify.
    – narkeleptk
    Commented Jun 10, 2020 at 2:36

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I assume you have already tested the battery with a voltmeter and found it over 11.9vdc. Do you have a jumpstarter? If you can jumpstart your car, then it means that the issue lies somewhere in the battery connectors, the engine ground or the battery itself. Eliminate all the possible causes one by one, and then you will find the root of the problem.

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  • That's exactly what I did.
    – PeaBrane
    Commented Jun 10, 2020 at 0:02
  • So it won't start even with a jumpstarter. Can you try to start it with the 2nd key? I've seen some times that some cars cannot decode the immobilizer code if the key is worn out.
    – TheBlackRazorGT
    Commented Jun 10, 2020 at 0:06
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    Engine shaking should mean that the starter works fine but no fuel is injected into the engine. Fuel pump, fuel pump connection or bad ECU.
    – TheBlackRazorGT
    Commented Jun 10, 2020 at 0:08
  • @PeaBrane any update on this? What was the issue?
    – TheBlackRazorGT
    Commented Jun 10, 2020 at 23:52

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