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Being used to driving manual transmissions, I occasionally forget to put my ATX in park when I shut off the vehicle ( I'm getting better ).

Today I did that without realizing it, and when I went to start the car it wouldn't turn over. I got out my multimeter, checked the battery voltage, then pulled the ignition fuse and checked if current was flowing.

What I saw was that I was getting about 164 amps over the ignition fuse when I would try to crank the engine, but it wasn't turning over at all, it didn't even seem like the starter was engaging, as I didn't feel any buck or movement of any kind. The very high current ( the fuse is only 40 amps ) makes me think the starter is engaging in a futile, energy intense struggle to turn the engine over, yet the total lack of any buck or other movement makes me think the opposite, that the starter isn't engaging at all. For example, if I put my manual transmission car in first with the parking break on and turn it over the whole car will buck.

This is on a 98 Mazda 626. So what's going on here exactly?

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    Have you really got a multimeter that can read 164 amps? Are the cables on it as thick as the starter motor cables? I think you must be making a mistake somewhere.
    – HandyHowie
    Apr 12, 2016 at 11:35
  • @HandyHowie I'll go back and double check later today.
    – Robert S. Barnes
    Apr 12, 2016 at 12:02
  • Yea, you're not pulling 164A through a 40A fuse. Something is up on your measurement. Also, federal regulations require that you place the car in park before you're able to remove the key from the ignition, so normally you can't "accidentally" leave it in drive unless you just leave the keys in the car. Maybe you can, but this rule makes it harder for most people to come across the situation.
    – JPhi1618
    Apr 12, 2016 at 13:27
  • @JPhi1618 You're probably right about the measurement being off. This is a European / International model, and I've accidentally left it in drive numerous times and not been able to start it until I realized my mistake.
    – Robert S. Barnes
    Apr 12, 2016 at 13:32
  • The point about wire size is well taken. If you were pulling 164 amps, even for a short time, through your multimeter that is probably rated for at most 20 amps, you would have a molten puddle of slag where your meter used to be. The wires and meter would become a fusable link and self destruct.
    – cdunn
    Apr 12, 2016 at 14:05

2 Answers 2

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There's usually an inhibitor switch that stops the current going to the starter unless the transmission is in park - on older vehicles, a mechanical switch activated by the linkage from the gear selector, but on newer stuff I'd assume it is inside one of the many computers...

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  • But why would I see such high current going across the ignition fuse? How does all that work?
    – Robert S. Barnes
    Apr 12, 2016 at 10:59
  • Yeah, that confused me too - I presume you're not getting any noise either, e.g. if the starter was turning but not engaging with the flywheel?
    – Nick C ♦
    Apr 12, 2016 at 11:01
  • I thought maybe I heard the sound of a relay closing, but I'm not sure, but other than that no sound at all.
    – Robert S. Barnes
    Apr 12, 2016 at 11:03
  • By the way, it's a 98 Mazda 626.
    – Robert S. Barnes
    Apr 12, 2016 at 11:10
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    I have a feeling you will find that it's 164 milliamps. Which would make a lot more sense. Some meters have readouts where the units are very hard to read, and easy to miss.
    – cdunn
    Apr 12, 2016 at 14:07
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So I happened to be looking at a wiring diagram of the starter circuit ( for an unrelated reason ) on my 98 626 and noticed that the relay which closes the starter circuit gets power via the transmission range ( or inhibitor ) switch which on 626's sits on top of the transmission under the air box:

enter image description here

So basically, unless the gear selector is in Park or Neutral there's no power to the relay and the starter won't engage.

Regarding the amperage reading, I'm guessing I must of had my meter set to milliamps, not amps.

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