12 Volt on the Block

Hello, this is my first Post so go easy on me :slight_smile:

2005 Honda Pilot has this strange Electrical issue. let me explain

Few weeks ago start hearing strange noise from Starter. had issues starting the Car. Juggling around the key worked for few days. then the truck would not start anymore. Battery fully charged no crank. Pulled the started out starter kinda fell apart. Put on new starter as soon as connected starter starter to spin without any key or staring position. Strange! I used a power probe to check to see if there is power on the connector. Noticed the entire body/engine had 12 volts power. disconnected the Ground from the terminal. Still 12 volt on the block. Negative/ground cable also had 12+ volt and causing large spark if terminal touched. disconnected the starter still 12+ volt on the block.

any idea where to start checking? Thanks

My first inclination is to say that your battery is installed backwards… Have you checked that?

No checked that. Only positive connected on red cable that goes to starter and fuse. Still 12V on body

I bet you the ignition wire going to the starter solonoid or the ignition switch itself is defective.Did you check that?

I do not know how you can get a voltage reading with the ground from the battery disconnected

Power probe picks up any voltage neg or pos

I checked that too. Disconnected both wires 1) straight from Battery 2) from the ignition
Still shows voltage on the block just pos terminal connected. Very strainge.

You are connecting the power probe to the negative of the battery then?

If the engine block has 12 volts on it that means it isn’t grounded properly. You also stated that the main ground wire has 12 volts on it. I assume you are using the battery post as your ground reference for whatever tester you are using. If that is correct then it means something is wrong with main ground connection at the battery. Possibly there is corrosion inside the wire or at the battery post clamp causing the issue. You may need to replace the main ground cable.

This kind of thing would be the same as removing the ground lead at the battery. With no ground to anything and only the positive wire connected, all the grounds would have battery voltage on them, using the negative post as your reference source. There is no return, current cannot flow since there is no return side of the circuit, so you see the full battery voltage on the grounds until a return to the battery for the ground connection is connected up. Ohm’s Law stuff.

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Yes i was using the battery negetive terminal as ground for the power probe while the ground was disconnected. Its seemed very strainge that positive volt was showing on the block. Power probe can pick up both + and - voltage.

Let me do some more testing. Unless the Red Battery cable is touching the body somewhere, main relay, or Alternator grounded etc.

If the positive side of the battery was touching a ground point that would normally cause a short and sparks would really fly if it wasn’t fused someway. In your case, not having a good connection to ground, having that happen would not cause a direct short. It is doubtful that you have a problem on the positive side of things, just the ground side. You will need to fix the ground side first before you really could determine if there is a further problem, which is unlikely.

You are not testing things as normal with that.

I think you may be misinterpreting what you are seeing from your voltage probing. The body and engine and battery negative are all connected together. Since your car worked before, unlikely anything on that has changed. An ohm meter should confirm the body/engine, and battery negative lead are all connected together. Do that test with the battery disconnected.

My guess is the sound you were hearing – the beginning of all this – was the starter motor failing. When you replaced the starter motor, perhaps you may have a problem in the power connections to it, maybe the two are shorting together. Easy to do b/c the visibility & access to that area is usually very limited. That would explain why the starter started to spin as soon as you connected it. The thick wire is connected directly to battery positive. If the thin wire was shorted to the thick wire the starter would turn on. BTW, before connecting a starter motor the battery is supposed to be disconnected.

I’m guessing the problem is that either the new starter motor install went awry, shorting the to aforementioned wires, or the replacement starter motor is faulty. There’s some slight chance the “S” wire (the thin one) has 12 volts on it all the time for some reason. It is only supposed to have 12 volts when the key is in start. That’s something your shop should check before hooking it up.

Put your power probe away and try a regular voltmeter. Red to positive black to engine with negative battery unhooked. If you are hooking your power probe negative lead to battery ground you are putting 12 volts to probe even if battery is disconnected.

Not strange at all. Without a ground reference, everything will appear to be at positive 12 volts. This is normal and not relative to your problem. Make sure you didn’t have connectors touching on starter. If you’re sure of that, take starter back to store and have them test to make sure it’s ok.

I think i narrowed down the issue. Ohm meter shows the main positive connector on the Starter is grounded for some reason meaning the new starter is probably not good. I have to pull that out and bench test that sucker. Thank you for all you guys input. just have not had time to dig into.

In your original post you stated that the starter motor was spinning while the ignition was OFF. For that to happen 12 volts would have to be applied to the solenoid contact lead of the starter somehow. You should check that out before removing the starter. By simply removing the ignition lead to the solenoid would stop the starter from running if that is the case. The problem could also happen if the solenoid contacts were stuck together internally. So if there is no problem with the ignition lead to the solenoid that would mean the contacts are stuck together.
I just thought that there is another way that this could happen. If you could have somehow tied the main battery cable from the battery directly to the starter motor instead of to the solenoid contact, that would do it. I assume that didn’t happen though.

You also stated that you saw 12 volts on the engine ground. The only way that can happen is to have a problem with the ground return lead to the battery. I suggest you remove the main battery lead from the starter and leave it isolated from the starter or touching anything else, especially ground. If you still have 12 volts on the engine ground then you have a bad ground cable.

That could also happen if the starter’s solenoid contacts were stuck in the closed position.

If you mean the B+ terminal on the starter motor, the one with the thick wire that connects directly to battery + post, you are right, that terminal should measure as an open circuit to ground (or starter case) with the battery disconnected. Make sure it isn’t the wire that’s shorted to ground by disconnecting both wires from the starter and re-checking the resistance to ground at the starter terminal. Note that the starter terminal with the smaller wire, the S terminal, will measure a low resistance to ground on a functional starter motor.