Won't Crank, good battery, good starter/solenoid

[Bob H]

My 99 Astro with only 70,000 miles suddenly won't crank. I swapped batteries with my Tahoe, same problem and the Astro battery cranks the Tahoe fine.
My positive cable had corrosion at the battery connection, I replaced the cable (the powder was into the wires not just the outside). that wasn't the problem either.
I read other threads on this forum for an hour last night, checked the 10amp crank fuse (and replaced it to be sure). that wasn't it. I replaced the starter enable relay (swapped it out with known good one) and that wasn't it.
I put a test light on the big fat hot lead on the solenoid (cable from battery) and of course that lit up. Then I put it on the smaller terminal from the ingnition (crank) side, and had the wife turn the key, and no light. therefore I am not getting the signal to the solenoid.
I have one of those tools that you can use to jump the solenoid (like putting a screwdriver across the terminals but has 6' wires so you can crank it from inside the vehicle) and it will crank and then start right up.
I looked for chewed wires to solenoid or from tranny neutral position switch and couldn't see anything obvious.
From what I have read here, it could be the ignition switch - but I do get electricity to the coil and it runs once jumped at the solenoid.
It could be the neutral position switch on the tranny - does anyone know how to track down the problem? I don't have the full manual, just the owners manual.
I am not a professional mechanic, but am familiar with fixing whatever goes wrong with my vehicles if it doesn't require a tool I don't have or can't get.

[Drummernaut]

This schematic is of my 99. I see a few fuses, a relay and a couple of switches to check. After fuses, I would probably start with the starter enable relay under the hood to see if it is clicking.

Hope the schematic helps.

[Bob H]

Thank you for the awesome diagram. I had my wife turn the key to "crank" position several times, and there was clicking from the starter relay under the hood. With the fuse / relay box cover off, I could see that there is an AC relay, starter relay, and another relay all with the same part number. I pulled the other 2 just to isolate and make SURE it was the starter relay that I was hearing clicking 0n-Off, and yes it is clicking.
1) this seems to tell me that the relay is OK, and the ignition switch is likely OK if it is getting signal to the relay when turned.
2) I'm not sure if the relay would "click" if the Park/Neutral sensor on the side of my tranny is bad. I'm not a pro mechanic - it's a bit hard for me to tell if the relay completes a circuit only if the Park/Neutral sensor is also good, OR if the relay can "click" but no current travels through that connection because the Park/Neutral sensor is bad.

One thing is for sure, I am not getting 12 volts to the solenoid and when I put 12 volts to the small terminal (jump the solenoid) it will crank right up.
The schematic shows a single wire going to the Park/Neutral sensor, and departing from it.
When I looked at it a couple days ago, seems it had about 4 wires going to the Park/Neutral sensor. and I think there were 2 "sensors" of some sort on the left side of that Tranny so I'm not even sure which one it is. I would love to isolate the wires that need a closed connection and bypass that Park/Neutral sensor to see if it is the problem.

[Drummernaut]

From what I see on the schematic, if that relay is clicking the the transmission and ignition switches are OK.

Looks like an open between the starter enable relay and the starter solenoid.

With the vehicle off, you should be able to do a resistance test between pin B4 on the relay and pin 6 of the solenoid. It should be shorted.

[Bob H]

OK I was wrong on the test to see if the starter-relay was "clicking". I just put a wooden chopstick on the relay and the other end on my ear - and it is not the one that is clicking. There are a bunch of relay's that fire when the key is put in the crank position - and the start relay isn't one of them. So maybe it is a bad "Park/Neutral sensor" or open connection somewhere.
With your help I did establish 3 things.
1) the terminal I am pointing to with a pencil goes to solenoid and has good continuity. And when I put 12 volts to that terminal, the starter cranks up fine.
2) the terminal I point to with the red probe is HOT when the ignition is on. All of the other terminals are cold.
3) turning the ignition key to crank/start does NOT ENERGIZE any of the other terminals. Basically nothing is happening to that relay by turning the key. And there are 3 identical relays (used for AC and something else). I swapped the 3 around and it didn't help - no crank. All 3 have the same part number, and wouldn't go out at once. I do hear the AC one "click" if it is in place and the key is cranked over to start.

[Drummernaut]

I added numbers to your picture. B6 is were the power needs to come from. If you probe B6 for 12V and have someone move the shift handle while starting may be you can get a small reading.

You can do the same at Crank Fuse #8. If you find voltage at fuse #8 but not at B6 your parking switch/circuit is at fault. If you have no voltage at fuse #8 with key at the start position you have a problem with you key switch/circuit in the steering column(bummer!!).

[Bob H]

THANK YOU for your help.
-The good news: it cranks and runs fine.
-Bad news: I'm not sure what fixed it.

I followed your latest advise, and went to check for voltage at "Crank Fuse #8". My helper is out of the house, I was having grief turning the key and putting the probes where they needed to be. So I looked at the 10 amp fuse that I had just pulled from "Crank Fuse #8" and was shocked to see that it was blown open.

I just checked that fuse yesterday, in fact I swapped it with one of the spares because another thread on this forum suggested changing that fuse even if it looked OK. I know it was OK, now it's blown. With a puff of dark soot, not a slow melt.

So I assumed that I blew the fuse today with all my probing around on the various pins on the starter-relay. I put in a new 10 amp fuse, and cranked & it turned over and started right up.

Looking back at the past few days, I am really puzzled. This van is a daily driver with only 70,000 on it. I pulled it up a few feet to get access to something behind the van, then it wouldn't start back up (wouldn't crank). I don't think THAT would have blown the fuse - and as I said I did check that fuse as one of the first diagnostics...

One thing that changed was pulling the wire to the solenoid and reconnecting it after checking for continuity. The fastener was on real tight, it's not like it was loose. So I dunno. Not sure why it wouldn't crank yesterday with an OK 10 amp crank fuse.
Again, thanks for your help. When I have time I am going to look really close at the wiring harness that I can access - and see if I have any hidden rodent activity. That has been a real problem where I live in the country. I did another post about rodents getting in my blower system (building nests) and getting into the interior of the van. There has got to be a partially chewed wire somewhere but I couldn't find it looking at the runs from the tranny switch, or near the various fuse boxes before the wires go into the black tube conduit wrap. Maybe I'll pull the engine cover /dog house and see if there's a rat nest & chewed wires that I don't see yet.

Could I have blown that fuse by putting a jumper to the solenoid to test the starter? I have never heard of that happening... just curious what caused it to blow.

[Drummernaut]

I have had the old double blow for no reason. I have had it tracing problems also. Could have been slight corrosion on the relay contacts, a not so perfect connection on the solenoid, a wire kink here and there?

Be happy!! Your through the woods for now.

[Bob H]

Yep - very glad it works.
Thanks for taking the time to help me. Electrical stuff can be a lot harder for me than mechanical wrench pulling.