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Thank you. I have a friend coming over tomorrow with an advanced scanner to see if it comes up with anything. I'll keep you updated and highly appreciate your help!
Scanner will be practically useless for this failure other than to see input and output state of BCM and PCM. Need to ohm that ground terminal in the relay socket to chassis ground to see if it is electrically connected and rule out a busted wire.
Dont we already know that is happening since OP is getting 12v at the relay coil when key is turned to engine crank? No way for that to get there without PCM and BCM being happy.
Im not really concerned with the 8v right now since it didnt happen when the key was in crank position. The 12v according to OP was there in crank position so thats all the relay coil needs for the hot side. Now im concerned about the ground side not being there which would explain his symptom of no crank. Wire could have gotten bit by a field mouse, pinched by something, damaged during a past repair or ?????? OP Jumping the contact side of the relay and engine cranks proves that side of it is all good. So he has a control side problem and it appears the 12v side of that relay coil is all good. I bet if he sticks a meter lead in the ground side socket and measure resistance to chassis ground that he will see way more than the 2 ohms or less that I would expect to be there. Those fuse boxes are pretty famous for corrosion underneath right where the wires come up to the fuse and relay socket terminals from underneath. The green crusties have been spotted there many times.
I see what you did there. Are you one of those neutral kinda guys. Swiss maybe?yep, we're on the same page.
I was just more focused on the + side of the circuit, being there are more connections. Then you show up and be all negative.
I took the entire Fuse box out yesterday, took it apart, removed all fuses and relays, removed the inside board and it was all clean. No corrosion. I will ohm the ground later when I get home. I'm praying it's something simple like a bad ignition switch but at this point, I have no clue anymore. The hardest part for me is the lack of symptoms. No crank/start and that's it. No thrown codes (to a regular scanner), no loss of power, good battery, good fuses, starter runs when jumped. I don't understand either why the relay is getting the 12v signal, along with the constant and you can jump it off its own ground terminal, yet it's not turning over the starter. When the starter is jumped via the relay, the engine turns over but doesn't fire. It just cranks. I'm assuming because I'm bypassing the other functions needed for it to operate like fuel and spark. It's hard for me to see a failed BCM or ECM without prior failure symptoms before ultimate failure. Who knows at this point. Hopefully this scanner later and help pin point something!
The fuses that matter, checked for continuity. All good.
I'll check it when I get home. I know what you're talking about. The firewall side is good. Haven't checked the engine side.
Nice sleuthing! We've seen corrosion take out the circuits on the bottom of the fuse block in the engine compartment and cause weird issues. So yes, you're likely on the right track.
That sure is odd. That circuit board doesnt appear to be a multilayer circuit board. So just the traces on the top there in the pic and likely ones on the underside as well. Not alot to go wrong there and if it does it usually shows a physical defect. Id have to so better pic and the ground terminals marked to see if your "bubble" is the culprit and it very well could be. The bubble can be bridged with jumpers on the trace of the board. Ive had to repair many obsolete boards over the years when I worked in the private industrial field. Running your own ground at the relay socket (top or bottom) is fine as long the correct wire gauge is ran AND the proper automotive rated wire with the correct temp rating is used. Remember it it always hot as hell under the hood of a vehicle.
Once I get it all back together I'll try a jumper ground wire. Appreciate the compliment.
So I went back again this morning and did some continuity tests from the top of the board, starter relay terminals, to the bottom of the board terminals that plug into the banks of wires that run to the other components. Relay terminal 87 (F1)(to 40amp starter fuse) has continuity and is good. Relay terminal 86 (C5)(to ECM starter relay) has continuity and is good. Relay terminal 30 (A)(hot at all times/main power) has continuity and 12v and is good). Relay terminal 85 (N5)(ground to engine block) has no continuity to the N5 terminal on the back of the board. I ohm tested the wire it plugs into under the fuse box on the vehicle, and it tested good for a ground. Since the computer is sending the crank signal, it's reading the key in the crank position, no theft control module is active, the starter jumped off the relay and worked, my only thought that it can be is the ground (N5) on the board. Without the ground it won't activate the relay. And I wasn't getting any clicking in the relay when we were trying to crank it yesterday. I'm attaching more pics of the "bubble". By the way, I also checked the N5 (ground) circuit which also leads to the ground terminal on the "run/crank" relay and I had continuity there so it does seem like there is a broken connection between the N5 plug on the bottom and the ground (85) terminal for the starter relay.
