Starter - keyed voltage

[Hoesgottaeat2]

Replaced (2) GM starters in the last 4-5 months. One was on a 2005 Silverado and the other on my ‘96 Burb.

I did them both on my lift. I’ve only had the lift for a couple of years so I find myself “doing a little extra” now due to the ease of having the vehicle overhead. So I figured while up in the air I’d test wiring integrity to the starter before the final conclusion of each replacement was determined.

On each vehicle, in both instances, I tested a constant 12V at the larger wire that connects to the solenoid. And in both cases I tested only around 2V at the keyed wire.

I was surprised to see such a small voltage to engage the solenoid.

What’s your $.02?

 

[Eman85]

Don't know how you measured 2V. GM starter solenoids use 12V and pretty high amperage which is why the wire is so heavy.

 

[Hoesgottaeat2]

The thicker wire tested a constant 12V, yes. But the smaller wire measured 2V, only when the key was engaged.

I agree, the starter motor itself operates on 12V, but to engage just the solenoid looks like it operates off of a lesser voltage. Sort of like a relay does.

When testing this and seeing it consistently across (2) different vehicles, it dawned on me that this could be the case.

I always have known it takes 12V to crank the starter, which is the larger current draw. But I have never heard discussed the voltage requirement of the solenoid itself, which likely draws far less current. But is the solenoid supposed to have 12V too when switched?

 

[Eman85]

When I say thick wire I don't mean the heavy battery cable, I mean the purple wire that activates the solenoid. GM starter solenoids do draw a larger amount of current than any other make which is why the heavy purple wire. I don't know where you're getting 2v from.

 

[exp500]

Wow, at 2v there, I would check my meter connections for corroded terminals or a bad ground. Also could indicate a bad starter switch if connections good. I forget, is there a fusible link in this wire? (also a possibility).

 

[Joseph Garcia]

Are you getting 2V when the solenoid is engaged (ignition switch in start position)?

 

[Hoesgottaeat2]

Please note here fellas, both starters have already been replaced and operate properly now. I checked this voltage when I had each starter out, on (2) separate GM trucks. When I measured 2V the key was in the start position each time. This had me uncertain each time that the starter was in fact the issue. However the starter replacement was the fix both times.

Just a bit of history here too...both mentioned vehicles had a no crank/no start condition prior to each of the starter replacements. I removed the solenoid wire and battery wire from each, and measured the following:

- Starter battery cable voltage (12V)
- Solenoid cable voltage .5V (key off)
- Solenoid cable voltage 2v (key in start position - using 2nd person)

Each time I measured voltage, I used the starter casing as a ground. Only thing I can think of is that the solenoid wire terminals I connected my meter to had some mild corrosion on them giving a false read? But to have the same results both times, in (2) separate vehicles, led me to wonder what the actual voltage there is supposed to be? With 2V seeming to be pretty low.

 

[Eman85]

You had a bad ground or a bad meter. You should have been reading battery voltage less whatever you dropped in resistance through the ignition and neutral safety switches. So basically 12v. Always ground your meter at the battery if you want a true reading.

 

[east302]

1996 diagram…

 

[Hoesgottaeat2]

You had a bad ground or a bad meter. You should have been reading battery voltage less whatever you dropped in resistance through the ignition and neutral safety switches. So basically 12v. Always ground your meter at the battery if you want a true reading.

I'll circle back to do this test again sometime as now I'm curious. Arriving at expected results will only add to my confidence of diagnosing something like this in the future. Just one more thing to overcome with salt belt related integrity issues. I'll ground at the battery next time like you advised. I assumed grounding at the starter case was sufficient as that is how I measured the 12V battery cable at the starter. Thanks for taking the time with me on this.