07 LT 5.3L Sudden no start/crank

J-Herkel said:

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.

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J-Herkel said:

Since the starter relay and the run/crank relay share the same N5 ground on the bottom of the board and the run/crank N5 seems to have continuity and the starter doesn't, I added a jumper wire. I'm going to see if it works. If so, this will be my permanent fix. This jumper is just a ground wire.

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rockola1971 said:

Your middle pic shows a trace that has acted like a fuse because the current passing through it exceeded its rating. So that trace heated up excessively and melted just like a fuse element does. You can lightly scrape the green color off of the trace on both good sides of the fused trace and install a jumper there by soldering a wire across the gap.

Now for 2 of the most likely causes to this trace failure. One is a poor connection at the stabs for the relay. This can be easily inspected to verify with a meter and visually. The other cause could be that the coil in your relay has partially shorted (not to be confused with short to ground). I would compare resistance measurements of your old coil in the relay and a new one. If you see the that old one has a coil resistance that is substantially lower than your new relay coil then you found the culprit. A coil is just that, a coil of wire that when energized puts out a magnetic field. A coil can fail in one of 2 ways. It can burn in half like a fuse and become open or it can have some, many, all of its wire coil windings melt together which overall lowers its resistance.

When a coil melts together and its resistance halves then the current feeding that coil doubles. Which means the traces in your circuit board for that coil (12v and ground) have to deal with double the amount of current that they usually handle and that amount usually exceeds its rating. As an example a coil that has 6ohm value into 12v yields 2a in current or 24w of power. If that same coil melts in half then it is now 3ohms and that value into 12v yields 4a in current (See...it doubled) and the power would be 48w. Power doubled also!

It is not a bad idea to replace relays in your vehicle every 5-7yrs. Maybe even more often in really hot climates like a desert state. They are cheap and this will avoid problems like this.

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j91z28d1 said:

should just be a few mA of current to close the relay contacts. the starter solenoid is grounded thru the block. the wire will be fine as long as it doesn't short something else out from rubbing on a positive tab. but I doubt that bubble is from a trace burning out. they always discolor the board if a short burns one up. more like it cracked from flexing or a bad solder joint somewhere.

gm has a history of circuit board failures. usually solder points break. not from bad factory solder but from moving around over time. I'm guessing lack of support designed into it. tons of cases where you take the module apart, reflow the solder and put it back together and alls good. from obs abs modules, to c5 corvette abs modules, even Gen 2 volt hybrid battery control modules. gm has a very long list of using badly designed circuit boards that fail over time.

I feel like this fix it fine. yeah, can't hurt to grab one at a junk yard if it's cheap and easy swap, but I don't know that if I'd go thru the hassle myself unless something else fails on it.

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