AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
12/4/21 6:48 p.m.

As some of you know I fell into a 96 SS for an amazing deal.  I really am enjoying fixing all of the little things wrong with the car, updating the suspension and brakes and driving it.  It makes very soothing V8 noises and oozes American Muscle Car.  I really want to get this car up and running again!

I have a big electrical issue.  On Veteran's Day I took my son out to brunch.  The car started and drove there perfectly just like it has been for me for a few months now.  After brunch, it would not start.  It doesn't crank at all.  There is no fuel pump noise.  There are no dash lights, no radio, nothing.  All the fuses are fine both under hood and on the side of the dash.  The car has new battery in great shape with plenty of juice.  The only thing that kind of activates is the door chime, sometimes, and sometimes you hear a continuous click of a relay.  The clicking bad relay is integral to the BCM.  I thought it might be the theft deterrent relay in the BCM, so I jumpered pins C2 and C11 on the BCM to bypass it per my shop manual and VATS bypass posts on ls1tech.  This should at least allow the starter to crank.  Nothing.  And the relay is still clicking inside the BCM continuously.  I have the BCM removed, but I cannot find a used on that is the same part number on ebay or any of the usual sites.  I know similar BCMs were in all F bodies 96-02.  I know about the bad soldering issues on the aux power relay, but that shouldn't cause a no start condition.

I have the VATS bypass module to generate the 50 hz signal for the ECM to fire the injectors and fuel pump, but with no starter engagement I seriously doubt that would work either. 

Lastly I know the VATS has the silly resistor key that sends a signal to the BCM, but the key worked right up until recently.  I suppose it could be a broken wire between the key and the BCM, but why is the car nearly 100% electically dead?  No lights, no turn signals, nada.....

I'm at a loss on this one.

https://www.youtube.com/watch?v=CtfROG06KAc

My BCM is part number 16206421 FYI. 

 

iansane
iansane HalfDork
12/4/21 7:35 p.m.

If you don't even have a consistent door chime I wouldn't be looking at VATS, I would be looking at the power supply to the car. Do 4thgens use the stupid fusible links by the starter like thirdgens did or did they wise up by then? Either way, I'd inspect the main ground cable from the battery and trace the power supply from the positive cable. But I haven't messed with 4thgens much at all other than stripping them of their engines/transmissions.

eastsideTim
eastsideTim PowerDork
12/4/21 8:07 p.m.

This may be a really stupid question, but have you checked the battery's condition?

APEowner
APEowner SuperDork
12/4/21 8:33 p.m.
iansane said:

If you don't even have a consistent door chime I wouldn't be looking at VATS, I would be looking at the power supply to the car. Do 4thgens use the stupid fusible links by the starter like thirdgens did or did they wise up by then? Either way, I'd inspect the main ground cable from the battery and trace the power supply from the positive cable. But I haven't messed with 4thgens much at all other than stripping them of their engines/transmissions.

I agree with this.  It really sounds like a basic primary wiring issue as opposed to some esoteric computer problem.  I seem to recall that those still used the traditional Chevy main starter lug as a power distribution point configuration.  If my memory is correct I'd start there.

Don't use a voltmeter to troubleshoot main battery wiring.  A bad connection can still show voltage.  Use a good old fashion incandescent test light. Or, just wiggle stuff.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) MegaDork
12/4/21 9:42 p.m.

Correct.  Not VATS.  If you have a chip failure (relatively common) in the key or the switch, it acts like a dead starter relay, or as if you didn't get it all the way into park or a bad NSS.  Everything will be perfectly normal, but it won't crank because it doesn't sense the correct resistance in the key.

If you get the VATS fail (which you probably will), there is a pretty easy fix.  The way it works is that GM programmed the BCM to sense resistance across the chip thing in the key.  Wrong resistance, no start.  The secret is to find the wire (might be wht or wht/red?  I forget) coming out the column and splice in a permanent resistor.  No more VATS, but also no more VATS no-start.

What you have sounds like a good old fashioned bad connection somewhere.  Start probing with a multi-meter when it's acting up.

The 96 SS is more old-school than new school.  The engine might be OBD2, but the wiring and chassis is throwback.  Nothing about the complexity of the OBD/ECM is causing this, at least nothing that I can think of.

jfryjfry
jfryjfry SuperDork
12/4/21 9:45 p.m.

Sounds just like a prob I had that was a ground issue.  Specifically the negative cable, though it looked great, had corroded to oblivion inside.  

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
12/4/21 11:04 p.m.

I was just out with the multimeter chasing cables.  I have 12.2V across the battery, but chasing the positive cable leads to really low voltages at various points and the cable end was warm to the touch like it was trying to short out somewhere.  I ordered new battery cables.  When I originally got the car they were corroded and pretty nasty.  I cleaned them up, but finding a voltage drop from the cable to the chassis positive terminal that powers many points on the harness is worrisome.  We shall see.  I verified no brake lights, nothing and brake lights are almost always universally right off the battery with a fuse and little else. 

The relay in the BCM may just be clicking due to lack of voltage and for the same reason the door chime might be acting silly too.  It may not have enough voltage to hold a simple relay closed.  We'll know soon enough.  I ordered AC Delco cables so fitment and ends will be perfect.  The positive has 3 leads (alternator, starter, and a chassis junction near the battery to many wiring harnesses).  The negative goes to the block and a hardpoint on the chassis near the positive junction box. 

 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
12/5/21 12:43 a.m.

Modules do wonky things when they get much below 9 volts.  Things like activating a relay, which pulls so much power that the module shuts down, which deactivates the relay, so the module wakes up... etc.

 

If the positive cable is getting warm even if nothing is on, that is odd.  But this is also one of those places where the side terminal batteries suck because you can't check the voltage drop between the battery post and the cable end.  Although on the side terminal batteries it is almost always a given that the connection is bad, and it's SOP to grab the cable and try to move it.  If it can move, it's loose, and things might just start working again smiley

But if the WHOLE positive cable is getting warm, I'd be starting to think about the tortuous path of the positive cable on its way to the starter, and all the different places it can rub through...

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
12/5/21 12:52 a.m.

In reply to Pete. (l33t FS) :

All the cables are disconnected until new ones arrive.  It wasn't hot, but I do not trust it at all.  I had been disconnecting the negative except while testing for the past weeks.  It's time to get this solved and on the road.  A warm cable end is odd though.  It was warm to the touch compared to ambient.  To me that means current was likely trying to flow but stuck due to high resistance.  

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
12/5/21 7:47 a.m.

Current WAS flowing.  The hot area was the load in the circuit.

 

The part that makes me curious is that, in any circuit, only as much current flows as the highest resistance in the circuit.  You could have megawatt light bulb in a circuit and there will be zero current flow if you turn a switch off, making its resistance infinite.  So if the cable was getting warm, enough current had to be flowing through it to MAKE it warm, which is going to be quite a bit.  It usually takes the kind of current draw like a starter running to make a battery cable heat up.  Just turning the key on shouldn't do that, heck it shouldn't make a 22 gauge wire get noticably warm.

 

So, again, the warm area was the load in the circuit.  But why was it getting warm in the first place, is the larger question.  There may be a short to ground somewhere.

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
12/5/21 5:58 p.m.

It was the positive so the starter may have been pulling current just not enough to crank the engine.  Or the starter may be shot and have fragged the cable too.  Cables are supposed to arrive Thursday.  It wasn't warm enough to be alarming.  It just seemed odd to me.

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
12/11/21 6:25 p.m.

Well it was indeed the positive cable.  I replaced both since the side mount bolt on the negative was also going bad.  The positive was pulling out of the connector at the bus terminal.  And the nut at the starter seemed loose to me (that would cause a warm cable too).  The main grounds by the bus terminal and on the block were fine.  I suspect starter was replaced recently and the nut was not tight enough.  I had to use a universal and a long extension and go over the crossmember by the motor mount to get it right enough.  The car started up more easily than it ever has since I've gotten it.  Tomorrow so can clean up the cable routing, too off the battery and work on the steering shaft rag joint.  It is back in my driveway and not on the street anymore!  I have lots of interior trim to put back too.  The front main weeps noticeably too.  
 

 

Opti
Opti Dork
12/12/21 9:53 p.m.

Dang sorry I didnt see this til just now. Glad you got it all fixed up. I love me a B body. Build thread?

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
12/12/21 11:09 p.m.

It's all in my wrongly named build thread.  This is an f body SS and not a B body though,  I've been eyeing those too.  It has that old school muscle car feel.  

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