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That is a lot of codes that sort of seem unrelated in the sense of it's not common that one would affect the other. I would start by investigating electrical connections, specifically the following areas.
#1) All battery connections including the positive terminal fuse block and black wire in the trunk.
#2) In the engine compartment, the positive terminals that attach the the fuse box. Verify any connection issue here or a loose nut for the positive wires.
#3) The fuse box under the hood itself. It it was ever removed and not re-installed properly, there could be loose connections underneath causing intermittent issues.
#4) Pop the passenger side front tire off and pull back the wheel liner side closest to the passenger door. Take a look at the ECU and its connections. Do any of them look loose or like they may have had water intrusion? They are pretty resilient but if water got in there, it could be a problem.
Hailstorm update: we thought both our house and our daughter's was water-tight; unfortunately, after a 2 inch rain Saturday night we found water staining at my daughter's house. That kicked everything into high gear for her, and I've spent the past several days working that crisis.
Today I started working your checklist. After cleaning some minor corrosion on the battery terminals etc. I was going to go for another test drive, and it won't turn over the engine. So I called my friend up and asked him when he'd replaced the battery last. He said "never". He then went on to say that he's got a new one at his house, so we're going to install that tomorrow and keep on diagnosing.
ETA: Each of my test drives is a minimum of 20 minutes, so I think that should be enough to bring a healthy battery back up to full charge.
Thanks again for that checklist; even after replacing the battery I think it'll be good time spent working the rest of those potential trouble spots.
Have a good one,
Mike
Last edited by VetteDrmr; Jun 21, 2023 at 04:57 PM.
Reason: Added test drive duration
Hailstorm update: we thought both our house and our daughter's was water-tight; unfortunately, after a 2 inch rain Saturday night we found water staining at my daughter's house. That kicked everything into high gear for her, and I've spent the past several days working that crisis.
Today I started working your checklist. After cleaning some minor corrosion on the battery terminals etc. I was going to go for another test drive, and it won't turn over the engine. So I called my friend up and asked him when he'd replaced the battery last. He said "never". He then went on to say that he's got a new one at his house, so we're going to install that tomorrow and keep on diagnosing.
ETA: Each of my test drives is a minimum of 20 minutes, so I think that should be enough to bring a healthy battery back up to full charge.
Thanks again for that checklist; even after replacing the battery I think it'll be good time spent working the rest of those potential trouble spots.
Have a good one,
Mike
Sounds like the battery is shot. A failing or bad battery in the C7 can create all sorts of issues. The ECU dials back the voltage output on the Alternator to as low as 11 volts at times to reduce fuel consumption. It isn't like the old school days where the alternator put out a steady current. Anyhow, if the battery has internal issues and drops voltage because of broken plate contacts inside and the ECU is commanding the Alternator to run in low voltage mode, then all of the sudden the entire system has less than 12 volts. This can cause all sorts of low power and voltage issues along with codes in the ECU.
TLDR; replace the battery before you do anything else.
I replaced the battery with a new one my friend had on the shelf for around 6 months (just never got around to installing it). Battery was totally discharged, so it took about 12 hours on my 8 amp charger and 36 hours on my battery tender. This morning the BT said it was fully charged, so I took it for another test drive. Checked the codes after startup, the O2 codes (sensor and heater) were gone. The only one left was a permanent code for the fuel pump controller, which I believe can only be reset by the PCM itself.
I tried to find every driving scenario I could, from normal city/neighborhood driving, highway, low power starts up an incline, hard accels, lugging up a slight incline in 8th gear at 50 mph, etc. No problems, and at the end of the drive cycle the fuel pump controller code had reset itself. Success!!!
The long term fuel trims are still always running negative, but closer to 0 than before.
I drove the car out to my friend's house to pick him up (40 minutes), and a return trip, still no problems and zero codes. He was quite excited to get his ride back.
I'm still not convinced that we've found the problem until he gets some more miles around the local area, but so far so good.
Thanks for all the help, and have a good one,
Mike
