07 LT 5.3L Sudden no start/crank

[tc8510]

Have you checked all your grounding wires? I had this same issue. It came down to my grounding wire that goes from the firewall to the top of the engine block. It was hanging on by a thread down by the block.

 

[TexasBob]

I am having what sounds like the same problem on an '03 1500 engine Yukon now. I fixed that particular grounding wire a few years ago. It broke because GM didn't leave any slack in it.

 

[J-Herkel]

Have you checked all your grounding wires? I had this same issue. It came down to my grounding wire that goes from the firewall to the top of the engine block. It was hanging on by a thread down by the block.

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.

 

[J-Herkel]

Alright so after some more diagnosis this evening, I had my buddy hook up his $7000 scanner and scanned the entire vehicle. The Theft Module is good. The BCM was good. The ignition switch is reading key postion correctly, the signal is being sent when the key is turned to the crank position. The ECM was good but detected a fault in the Start Relay Circuit (P0615). So we used a schematic and traced the wires to the connectors below the Fuse box that the Fuse box itself plugs into. We tested the relay terminals. 30 is good (12v). 87 is good (12v). 86 is good. 85 (ground) is not good. No reading. We took the fuse box off and out and tested the terminals on the plugs below. The power (+) side to the relay is all reading. The ground (-) is also reading fine. Next I pulled apart the fuse box and we tested the contacts on each side of the board. The power side has continuity. The ground terminals do not. We touched the relay ground terminal to every terminal in that bank that it leads to and no continuity. As weird as it sounds, it seems like the fuse box relay circuit went bad on the fuse box circuit board. I'm assuming I can put it all back together, use a thin wire and stick it in the ground side of the relay, ground it to the frame, insert the relay and see if it cranks. Thoughts? Ideas? I'm not an auto mechanic but I'm doing my best here.. I did see a little bubble on the board. Maybe it has nothing to do with it. Idk. I'll attach a picture.

 

[Geotrash]

Alright so after some more diagnosis this evening, I had my buddy hook up his $7000 scanner and scanned the entire vehicle. The Theft Module is good. The BCM was good. The ignition switch is reading key postion correctly, the signal is being sent when the key is turned to the crank position. The ECM was good but detected a fault in the Start Relay Circuit (P0615). So we used a schematic and traced the wires to the connectors below the Fuse box that the Fuse box itself plugs into. We tested the relay terminals. 30 is good (12v). 87 is good (12v). 86 is good. 85 (ground) is not good. No reading. We took the fuse box off and out and tested the terminals on the plugs below. The power (+) side to the relay is all reading. The ground (-) is also reading fine. Next I pulled apart the fuse box and we tested the contacts on each side of the board. The power side has continuity. The ground terminals do not. We touched the relay ground terminal to every terminal in that bank that it leads to and no continuity. As weird as it sounds, it seems like the fuse box relay circuit went bad on the fuse box circuit board. I'm assuming I can put it all back together, use a thin wire and stick it in the ground side of the relay, ground it to the frame, insert the relay and see if it cranks. Thoughts? Ideas? I'm not an auto mechanic but I'm doing my best here.. I did see a little bubble on the board. Maybe it has nothing to do with it. Idk. I'll attach a picture.

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.

 

[rockola1971]

Alright so after some more diagnosis this evening, I had my buddy hook up his $7000 scanner and scanned the entire vehicle. The Theft Module is good. The BCM was good. The ignition switch is reading key postion correctly, the signal is being sent when the key is turned to the crank position. The ECM was good but detected a fault in the Start Relay Circuit (P0615). So we used a schematic and traced the wires to the connectors below the Fuse box that the Fuse box itself plugs into. We tested the relay terminals. 30 is good (12v). 87 is good (12v). 86 is good. 85 (ground) is not good. No reading. We took the fuse box off and out and tested the terminals on the plugs below. The power (+) side to the relay is all reading. The ground (-) is also reading fine. Next I pulled apart the fuse box and we tested the contacts on each side of the board. The power side has continuity. The ground terminals do not. We touched the relay ground terminal to every terminal in that bank that it leads to and no continuity. As weird as it sounds, it seems like the fuse box relay circuit went bad on the fuse box circuit board. I'm assuming I can put it all back together, use a thin wire and stick it in the ground side of the relay, ground it to the frame, insert the relay and see if it cranks. Thoughts? Ideas? I'm not an auto mechanic but I'm doing my best here.. I did see a little bubble on the board. Maybe it has nothing to do with it. Idk. I'll attach a picture.

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.

 

[j91z28d1]

Alright so after some more diagnosis this evening, I had my buddy hook up his $7000 scanner and scanned the entire vehicle. The Theft Module is good. The BCM was good. The ignition switch is reading key postion correctly, the signal is being sent when the key is turned to the crank position. The ECM was good but detected a fault in the Start Relay Circuit (P0615). So we used a schematic and traced the wires to the connectors below the Fuse box that the Fuse box itself plugs into. We tested the relay terminals. 30 is good (12v). 87 is good (12v). 86 is good. 85 (ground) is not good. No reading. We took the fuse box off and out and tested the terminals on the plugs below. The power (+) side to the relay is all reading. The ground (-) is also reading fine. Next I pulled apart the fuse box and we tested the contacts on each side of the board. The power side has continuity. The ground terminals do not. We touched the relay ground terminal to every terminal in that bank that it leads to and no continuity. As weird as it sounds, it seems like the fuse box relay circuit went bad on the fuse box circuit board. I'm assuming I can put it all back together, use a thin wire and stick it in the ground side of the relay, ground it to the frame, insert the relay and see if it cranks. Thoughts? Ideas? I'm not an auto mechanic but I'm doing my best here.. I did see a little bubble on the board. Maybe it has nothing to do with it. Idk. I'll attach a picture.

you might not think you're a mechanic but this is better trouble shooting than most mechanics can do these days.


definitely add a ground to the relay and see if it all works, if so you might consider picking up a new fuse box at a junk yard. Just incase it starts having issues to other relays long term.