Corolla starter mysteriously shorts

[marc.spehlmann]

Hello!

My 2000 Toyota Corolla occasionally blows a 5 amp fuse that protects the starter.

I don't have a background in electronics but from what I've read I think this is due to a short somewhere in the starter circuit. So I imagine that my solution is clearing the short.

It seems weird to me that this problem is recurring (it happens reliably every few months), and that my solution solves the problem.

The process to fix the car is:

1. Try starting it by replacing the fuse and turning the key. Blows the fuse.

2. Get under the car and unplug the plug that goes into the starter. There's 2 plugs, I unplug the smaller one which I take it to be a control plug and not the power plug.

3. Plug it back in. Replace the fuse.

4. Car starts

Sometimes I try just shaking the wiring bundle that leads up to the starter, thinking that this might clear the short- it doesn't. Not until I unplug/plug back in again.

Before I learned about this reliable 4 step process, I tried a number of other things:

• replaced the starter motor entirely
• hit the starter with a crowbar
• replaced the box of relays in the main engine compartment.

None of these worked (except replacing the starter, but that's not a good solution because it takes a lot of effort and money, plus the starter is not broken).

Any one have some insight on what might be a reliable long term solution to this problem?

Thanks- Marc

[Tester]

That 5 amp fuse protects the coil in the starter relay.

The coil in the relay may be drawing too much current causing the fuse to blow.

Try replacing the starter relay.

Tester

[marc.spehlmann]

I already have replaced the relay by way of replacing the box of relays in the engine compartment. ¯\_(ツ)_/¯

[BillRussell]

replaced the starter motor entirely

You did or did not replace the starter?

[Tester]

Automatic or manual transmission?

And does it have an anti-theft system?

Tester

[marc.spehlmann]

I replaced it with a new starter motor about 2 years ago, yes.

[marc.spehlmann]

Tester- It has a manual transmission.

[Tester]

Here's how this circuit works.

From the ignition switch, a red wire goes to the 5 amp fuse.

From the 5 amp fuse, a black wire with a white stripe goes to the clutch pedal inter-lock safety switch.

From the clutch pedal inter-lock safety switch, a black wire goes to the starter relay coil.

From there a black wire goes to ground.

Tester

[insightful]

Get under the car and unplug the plug that goes into the starter.

Could you be getting water into that plug (rain/splashing)?

[marc.spehlmann]

It's unlikely. Several times it has happened, there's been no rain for several months.

Now that I think about it, the short does seem to be associated with heat. I cannot remember a time that this happened and it wasn't the summer. But, that said, I can drive it out in hot weather and not experience the issue.

[Barkydog]

Given @testers fine description my guess would be the starter relay coil, I do not know if that can be serviced. It may be the fuse is blowing after the last start, not when attempting a start.

[marc.spehlmann]

Thanks all for the tips. I will follow the instructions on this youtube video (once I find someone with a multimeter) and then post back.

[kurtwm2010]

a multi-meter probably won't do much good. You will need an amp meter that measures DC voltage to see the current consumption at the time the starter solenoid kicks and the starter starts the engine. Since the fuse blows only occasional, you may have a hard time getting the measurement you need. If you are lucky it is borderline and you can get an idea how many amps are drawn.

By the way.... step #2 in your original post does not do anything of value.

Replacing the "box of relays". What relays?

[marc.spehlmann]

You will need an amp meter that measures DC voltage to see the current consumption at the time the starter solenoid kicks and the starter starts the engine

Sounds sophisticated for what I know about cars. But it's useful for reference if I take it to someone when it's happening.

step #2 in your original post does not do anything of value

Well, it gets the car going again However, my guess is that the unplugging part isn't the important part but just jostling the wires around is enough to clear the short.

Replacing the "box of relays". What relays?

I am including an image of the box-o-relays

[BillRussell]

an amp meter that measures DC voltage

To measure DC voltage you don't need an "amp meter", you need a voltmeter, which you can get for $10.

An "amp meter" or ammeter measures current.

[kurtwm2010]

An "amp meter" or ammeter measures current

Correct, and that's what you want to measure, in this case, to find out why a fuse blew.

[GeorgeSanJose]

Here's how this circuit works.

From the ignition switch, a red wire goes to the 5 amp fuse.

From the 5 amp fuse, a black wire with a white stripe goes to the clutch pedal inter-lock safety switch.

From the clutch pedal inter-lock safety switch, a black wire goes to the starter relay coil.

From there a black wire goes to ground.

I own a vintage Corolla and have battled with the starter motor circuits from time to time myself. From what Tester says your problem is not likely the starter motor. The circuit Tester describes above powers the coil in a small starter relay that is located under the dashboard, in the passenger compartment. If located similar to my Corolla, that relay is near the driver's left knee, plugged into a relay plate aside various other relays. The ignition switch/fuse powers the coil on that relay with the key in "start", and the contacts on that relay power the starter motor "Start" signal (the smaller of the two connectors on the starter motor). On my Corolla there's another fuse for the starter signal to the starter motor, but that is usually a 10 or 15 amp fuse, or maybe even higher.

So what to do about all this? hmmm .. well, if OP could post a wiring diagram of the car's starter motor circuitry, that would help. Absent that, probably first thing to do it disconnect the small wire on the starter motor and use a volt meter to see if the "start" signal from the starter relay contacts is reliably reaching the "start" wire at the starter motor with the key in "start". It should read nearly the same as the battery voltage with the key in "start".