Code P1780 intermittent no start issue?

I just sent an email to G7 describing what happened after I installed the repaired BCM and asking for any advice, as well as the faulty component they replaced (as that might provide a clue to the source). I have also been thinking; the gas gauge is a reliable indicator of whether the engine will fire or not, if there is a relay that controls the gas gauge and the ignition, either the relay is faulty, or it is not getting a reliable signal. Possibly Saturntech knows what relay to look at. I assume that the relay is activated by grounding one of the terminals, I could ground that terminal and see if the gas gauge reads and if the engine starts. Then look for the reason it isn't getting a signal.

I sent a complete report to G7 of what happened when I installed the BCM. I did not even suggest that there might have been any error on their part. I said I might have fried the BCM by not looking for any fault in the systems external to the BCM before connecting it. I only asked for their help in isolating the circuit(s) involved so I could narrow my search for a fault to those areas. I received the following in an email from G7 this AM.

"Okay. You can send it back or I can issue a refund. There must be an intermittent or latent fault inside the computer. The nature of intermittent faults is that they appear and disappear at random, and therefore make it very difficult (sometimes impossible) to detect. It tested OK after we worked on it, but it just might not have been failing then. Or there could be something wrong with our equipment. If you send it back, there is a possibility that the damage is too latent or extensive for repair.
Thanks"

Hi Joe,

I've been looking at the BCM diagrams you sent, I see nothing that looks like it controls the gas gauge or spark (ignition). It appears that IGN 1 is what powers up the BCM (or some of its functions in Start or Run), IGN 2 is hot at all times.

Would you be able to send me a copy of the under-hood fuse block wiring diagram? That might help me locate the circuits that the trouble is related to.

Thanks.

Looks like I might need both. I want to see what I can learn before I send the BCM back to G7.

Hi Saturntech9,

Thank you, that was the idea I had gotten from your earlier posts. I'm going to send the BCM back and hope they can catch it. I know that intermittent issues can be hard to find, and I have no idea how their testing is done, so I'll send all the data about what I've observed, and hope that helps them find it.

Thank you Saturntech9, and Merry Christmas to you and all the crew at 2CarPros. Bob

Hi guys, here's the latest: I returned the BCM to G7 on their offer to re-check it, when it was returned, there was no communication included and I still have the same problem. I discovered I can get a new GM replacement from Rock Auto for less than the price of repair, it will however require re-programing. What will I have to do to re-program the new BCM?

Thanks Joe, I'll check to see who can do this. Bob

Thanks, will do.

Hi Joe,

I contacted my closest GM dealer and the service manager said they could do the re-programming. He said to bring the car in, and they would diagnose the problem and fix it, only cost me between $300 to $1200, depending on what they found.

Some months ago, I took the Saturn to a non-dealer shop for an estimate to replace the water pump, they said they detected hydrocarbons in the coolant and would need to replace the engine with a used one and had the estimate for repair over $4,000.00. I took the car home and replaced the water pump myself and never had a problem of losing a drop of coolant. While there may have been hydrocarbons in the coolant, it didn't make a bit of difference.

What I'd like to ask is if there are more wiring diagrams that could help me locate what actually powers the ignition. The diagrams you did provide were very helpful, but I haven't been able to find what powers the fuel gauge or ignition. I want to see if I can bypass the fault.

Thanks, Bob

Thanks Joe! I'll dive into this and let you know what I learn. Bob.