[SOLVED] Starter voltage question

1998 Subaru Legacy Outback...2.5L engine.
Just a question regarding voltage readings on a sticking starter solenoid (essentially a basic electrical question). Intermittent sticking starter is causing starting issues when hot. When it's sticking, backprobing the S post connector yields about 6v. Unplugging the connector gets me 12v at the connector. My question is just a basic electrical one...why, when the starter is sticking, am I getting 6v when it's plugged in?
Hope that makes sense. Wacking the starter gets it going every time. So I'm relatively sure the voltage I'm seeing is a SYMPTOM and not a cause of the no crank. Just curious about this voltage reading and where those other 5v are going when there's no movement.
Thanks for any info!
Rob

Brown wrote: 1998 Subaru Legacy Outback...2.5L engine.
Just a question regarding voltage readings on a sticking starter solenoid (essentially a basic electrical question). Intermittent sticking starter is causing starting issues when hot. When it's sticking, backprobing the S post connector yields about 6v. Unplugging the connector gets me 12v at the connector. My question is just a basic electrical one...why, when the starter is sticking, am I getting 6v when it's plugged in?
Hope that makes sense. Wacking the starter gets it going every time. So I'm relatively sure the voltage I'm seeing is a SYMPTOM and not a cause of the no crank. Just curious about this voltage reading and where those other 5v are going when there's no movement.
Thanks for any info!
Rob

The 12v you measured was on the S post terminal of the starter, connector unplugged, starter continuing to crank on its own?
And with the connector plugged in and backprobing, you're reading 6v? And again, while the starter is continuing to crank?
Also I am guessing unplugging the solenoid S post wire does not fix this isse.

If the above is correct, what you are reading is a backfeed of the pull-in winding circuit and is completely normal. That circuit gets it's ground through the motor circuit BEFORE the motor engages. Once the motor gets energized, what was a ground, is now a power. With the circuit plugged in, your getting a partial voltage drop across the winding (in reverse direction). With the connector unplugged you'll read 12v.
This 12v is coming from the positive brush circuit, through the pull-in winding in the reverse direction.
I hope that makes sense.

Brown wrote: 1998 Subaru Legacy Outback...2.5L engine.
.why, when the starter is sticking, am I getting 6v when it's plugged in?

I think what he means by sticking is "just a clicking noise" and not cranking on it's own or stuck cranking, because he later said

Brown wrote: Wacking the starter gets it going every time.

As GeorG helped clarify, I'm reading 6v backprobing the connector at the S terminal while the engine is a "no crank"...starter just clicks, and I get the 6v...connector plugged in. In such an instance, is the partial voltage drop you describe above happening? Or is it something else?
Thanks for the insight! I realize this would be so easy to describe if we could look at it together, but that typing it out makes it way more complex than it needs to be:-)
Rob

RobBrown wrote: As GeorG helped clarify, I'm reading 6v backprobing the connector at the S terminal while the engine is a "no crank"...starter just clicks, and I get the 6v...connector plugged in. In such an instance, is the partial voltage drop you describe above happening? Or is it something else?
Thanks for the insight! I realize this would be so easy to describe if we could look at it together, but that typing it out makes it way more complex than it needs to be:-)
Rob

Thanks for clarifying guys. Sorry I misread that.
To clarify further. You have 6v on the S post during the no crank problem and you are smacking on the solenoid to get it to work?
I would like an amperage reading on that wire during this 6v period if possible

Exactly! Driving to PA this weekend. I'll take my Vantage and amp clamp and try to catch it and update when I can.

I thought he was talking about a starter run on as well. I actually had a rather lengthy reply typed out, and then realized he may be asking a different question than what I was answering and chose not to post it. :huh:

Are you talking about a constant 6v or only with someone holding the key in the START position?

Eager to hear the result of this current measurement. 6V on that wire during a no crank would typically indicate a voltage drop. So, tapping on the starter shouldn't help, but does! I would think that if the solenoid was shorted, then it'd burn a fuse or fusible link.

I'm wondering what would happen if you get this thing not cranking, and instead of tapping on it, just a jumper wire connected to B+ and touch on the S post. In my head, this would help clarify if this is a starter problem, or a solenoid circuit problem. Thoughts?

Tyler, Noah:
The 6v is only present with key in START. Voltage at the S terminal connector always drops to zero with key in any other position. Again, that 6v is ONLY when the connector is plugged in, backprobing, key in START position, engine a "no crank". If I disconnect the connector and take the reading, key in START, at the now disconnected wire coming from the inhibitor switch, I ALWAYS see 12v, even when the engine isn't cranking. That makes me assume that a jumper wire to the s post wouldn't make a difference...because I ALWAYS have 12v on that wire (but now that I'm remembering..."no current flow, no voltage drop"...so it would make sense that I'd see 12v there EVEN IF there were excessive resistance in that circuit...hmmm...so I'll definitely try a jumper to the S post.)

Still planning to get an amp reading...and I'll now also try to hit the s post with a powerprobe when it next flakes out. (Going to have to be carrying around a lot of expensive gear in my car! )

(Going to have to be carrying around a lot of expensive gear in my car! )

:huh: Doesn't everyone drive around with $10,000 worth of diag equipment? :dry:

RobBrown wrote: Tyler, Noah:
The 6v is only present with key in START. Voltage at the S terminal connector always drops to zero with key in any other position. Again, that 6v is ONLY when the connector is plugged in, backprobing, key in START position, engine a "no crank". If I disconnect the connector and take the reading, key in START, at the now disconnected wire coming from the inhibitor switch, I ALWAYS see 12v, even when the engine isn't cranking. That makes me assume that a jumper wire to the s post wouldn't make a difference...because I ALWAYS have 12v on that wire (but now that I'm remembering..."no current flow, no voltage drop"...so it would make sense that I'd see 12v there EVEN IF there were excessive resistance in that circuit...hmmm...so I'll definitely try a jumper to the S post.)

Still planning to get an amp reading...and I'll now also try to hit the s post with a powerprobe when it next flakes out. (Going to have to be carrying around a lot of expensive gear in my car! )

Nice job so far, especially your "no current flow, no voltage drop" comment! You're on it man!
Okay, so you understand my thought process here.
We either have a voltage drop issue on the S post OR the solenoid is shorted and is drawing excessive current flow, which is heating the solenoid wire to a point of causing the voltage drop.
The amp reading is absolutely key here. Make sense?

RobBrown wrote: That makes me assume that a jumper wire to the s post wouldn't make a difference...because I ALWAYS have 12v on that wire (but now that I'm remembering..."no current flow, no voltage drop"...so it would make sense that I'd see 12v there EVEN IF there were excessive resistance in that circuit...hmmm...so I'll definitely try a jumper to the S post.)

Yep, you got it! I've had HEATED arguments with 20+ year technicians that don't get this concept.

I probably should have specified a fused jumper wire previously, given the possibility of a shorted solenoid... Or, watch for the breaker to pop on your Power Probe!

Tyler wrote: I'm wondering what would happen if you get this thing not cranking, and instead of tapping on it, just a jumper wire connected to B+ and touch on the S post. In my head, this would help clarify if this is a starter problem, or a solenoid circuit problem. Thoughts?

It will likely not crank, I suspect that this starter has very short brushes, which will produce heat(which accounts for the voltage drop) when not fully touching the commutator, but when he hit's the starter they make contact and crank.
I think :whistle:

We'll see!

Thanks for the continued help, guys. I haven't updated only because the issue hasn't reappeared since my last post. Still waiting for the opportunity to get the amp reading and try the fused jumper. Thanks for your patience!

No worries, thanks for checking in with us. I'm glad it hasn't stranded you recently!

Reading back over the thread I see no mention of checking the battery voltage across the battery while the starter is operated but engine is failing to crank. .

Thanks for your continued patience, guys. It's starting to act funky again, so I'm very hopeful I can get an amperage reading (and perform the other tests you all have suggested) this weekend. I'll keep you in the loop!

Take a voltage measurement at battery while cranking, then at starter post (cranking) not cable, solenoid and starter post, if voltage is the same it is the starter if not check cable and connection.

Okay...so I finally checked amperage draw on the s post wire while cranking. UNFORTUNATELY, I never got a reading while the car was a no-crank. However, my amperage reading (using an inductive probe on a 1v=10A scale) showed a 20amp initial spike every time when the car WOULD start. Again, this was with the car starting. Is that normal?

There have been a couple times this week when the starter has failed to crank on the first attempt. But it always fires up immediately on the next one. Making it really hard to get any sort of reading (voltage, amperage, or otherwise!) on the failing system:-(

Rob