So I hopped in the truck tonight and ran to Lowes after work, slow to start, but the stamp on the battery says 2008. I knew it was getting close to time to put a new one in, but was being lazy and put it off. Fast forward to leaving Lowes, and now it's REALLY slow to start, like I thought I might need a jump slow to turn over. But she caught, and was running fine. Go to leave, and it's like I've got no power. Like it's trying to suck air through a 50' intake track no power.
After a few choice words, I decided to see what I could figure out knowing that the battery was already suspect, I thought MAYBE, not enough juice to the coils. So I puttered home, and hopped in the wifes car and went to dinner with her. To which she tells me "oh BTW, car has been really slow to start last two days." 
BERK! So we go to dinner. Come out, and it BARELY catches. So we drove straight to wally world and picked up a pair of their batteries, one for mine, one for hers. Got home and installed them, and everyone is cranking fine now.
The truck though is still locked in 3rd when in drive. If I pull it back manually I can get second, but first isn't happening, and neither is 4th. Googles are telling me that the ignition switch going bad can cause this to happen suddenly, also says it could be causing the wonky fuel gauge. (figured it was just another GM sending unit going bad, as it would randomly tell me I was out of fuel then pop back over to where it should be)
Anyone have any experience with these things?
Oh and it's a 2000 1500 ext cab 4x4 with a 5.3 if it matters.
Best bet is to find someone to scan it. The low voltage could have confused something, but the battery disconnect should have fixed that.
My 2001 GMC Savana has done that twice, it was the transmission fuse. On mine the odometer also goes dark.
I replaced my ignition switch between the first and second time the fuse blew. Ignition switches can cause this. Also found the ground was bad on the thermostat housing. Two months now no blown fuse.
Your transmission is in limp mode for some reason, you should have 2nd gear also if you manually shift. Either no power to it or one of the $8 solenoids shorted. If my fuse blows again it's getting the whole shift servo kit $45, two solenoids filter and a gasket.
Possibly unrelated, but the transfer case encoder failed on my buddy's 2003, which resulted in going into limp mode, and no converter lockup. He had a 'service 4wd' message on the dash though.
It will be tomorrow evening before I can get it somewhere to have the codes pulled. Went looking for a transmission fuse, but I can't find it, or what it would be labeled as. I'm relieved it's only in limp mode, and not blown up, but I'll be damned if I can figure out what caused it to go into limp mode.
Streetwiseguy wrote:
Best bet is to find someone to scan it. The low voltage could have confused something, but the battery disconnect should have fixed that.
I've found my GM vehicles to be slow to forget things on occasion. I had a similar issue once, and the answer was to leave the battery unhooked over night. Worked fine after that, but shorter intervals were no good. In fact it was a 2000 as well, though a Pontiac Grand Prix. I imagine a capacitor or similar holding charge fora while is the cause, but could come up with a few other possibilities as well.
I'll pull it tonight when I get home. Thanks for the heads up!
YEAH, start with pulling the neg cable. Give it time. I know low voltage can cause all sorts of wierdness with ecm's.
The fuel gauge sounds like mine. It's only accurate right after a fill up and it shows full. Any time after that, it's all over the place. Been like that for 3 years now. I just never go over 400 miles before filling up.
Jags get pissy with low voltage conditions. I've learned that before hooking a battery up, it's best to touch the pos and neg cables together for a minute or so. If you are disconnecting the battery tonight, might as well try it.
Is it possible the bad battery took the alternator with it (dirty power)?
I hope not... I just put a new one in 2 months ago. 
In my van the fuse is left of the brake pedal. #19.
Well.... It's working. Don't ask me how, but it's working.
Hooked the battery back up. (twice, because for some odd reason if the fan is on when you hook up the battery, the truck will start but not stay running. )
Drove it into town. STILL only had 2nd and 3rd. 2nd only if I selected it manually. Stopped by an Advance auto parts, and asked them to scan it for codes. Either my truck is possessed or the guy had no clue, as he couldn't get it to read the codes. So I said C'est la vie, and went down the road. Literally, it was working perfectly when I left Advance.
C'est la vie. LOL My truck isn't happy with me or something. Though it's scheduled to go to my cousin's place in the spring for new rockers, and fabricated bumpers. Think Road Armor style. probably respray it after the new rockers once he has the measurements for the bumpers. Thinking about custom frame sliders to go with the bumpers, though it rarely see's off road off the farm.
ECMs can do some weird stuff sometimes.
My last work van before the one I have now was a 2005 GMC/Duramax cargo van. It had an intermittent glitch that would prevent part of the electrical system from powering up when the key was switched on, but it was intermittent, only a couple of the idiot lights on the dash would light at key on, and it would crank, but not start. For six months the boss didn't believe me, until the day it happened at the shop. The dealer couldn't get it to do it long enough to get a good diagnosis (as an electrical technician myself, I know how frustrating that is). The dealer recommend replacing the dash and ECM, my boss said no, got me a new truck, and let the wonky one sit in our yard. Two years later, someone needed a spare truck, and that was the only one available. Its was put back into service and has run almost a year without incident. Weird.
My friend had an ECM electrical glitch with his Suzuki sx4 a few months ago. It was running pig rich, and had faults for long and short term mixture being rich. It had a seemingly bad signal from the upstream O2 sensor, but no related fault codes. I disconnected the O2 sensor with the engine running to provoke a fault code, but nothing happened. When I cleared the existing faults, everything started working normally again. Weird.
