Hagar68

There is a tsb to update abs software. It fixed my 2020

Our 2020 started this in Feb at 16k miles. Dealer programmed the transmission to "relearn" last week and so far it is smooth again.

Thanks for your updated thoughts Dr1ft3r. I also had decided to stay segregated. I currently just have 2 big traditional batteries in the bed and tie them together but separate from the truck and keep them AC charged at the house (I'm don't keep the receiver winch on the truck except when it might be needed). The DC/DC charger is a really good idea to get on-board charging while protecting the truck systems. I would love to have a bigger alternator or even the 2 on the snow plow pkg, but you don't find many of those options here in the south.

Thanks. The jumper cables are a good way to get the heavy wire. I did something similar with Andersen plugs as well. Did you connect negative cable to battery, or to the negative stud on passenger side of hood? Any codes set when you run the winch?

2020 GMC Sierra 2500 gasser, base 170 amp alternator, 1 battery as built. Want to install receiver winch but hesitant to wire it into all these computers. I know the truck measures total amp load thru a doughnut at the negative terminal, and that computer will actually increase idle rpms if alternator can't keep up. Winch draws almost 400 amps full load, which would seem to look like a dead short to the computer. How are folks powering these winches in these newer trucks without damage or setting a CEL?

2020 GMC Sierra 2500 gasser DOUBLE cab. Sticker 6987 curb. On the way home from Tenn where I bought it, 7230 lbs on the cat scale, with 215 lbs of me and 30 gallons of fuel on board. 10,000 gvwr

I have both issues on my 20 gas hd. Experienced the first decel/Accel burp under 1k miles, in tow/haul while pulling travel trailer. Only once in a while since then. The harsh down shifts from 2 or 3 are either getting more frequent or I'm listening for it more. 2.5 years old but only 15k miles

a little off the OP, but I did this calculation last night of my 18 spare vs 20 tires and the 3/4 difference. That sure seems like a lot of difference for the rear differential. Stunning they would do this on purpose. I think a full size spare will fit. Going to try it when I rotate next week.

Just wondering if the OP found a solution? My 20 GMC 2500 started doing this last week, around about the time I "postponed" on-star update V4.25. I've declined 2 prior updates, in fact I've never accepted an update. My radio (and window operation) are staying active for about 6 seconds after the driver door is opened. It is supposed to go off instantly when the door opens, and always has. My courtesy lights come on the instant the door is opened, so it isn't the door switch. I've called 2 dealers and both were very familiar with problems with the RAP (retained access power) system but neither have mentioned a connection with onstar updates. However, several comments on 2 other content strings here where they allowed the updates and the radio-on issue went away. I just don't trust On-star and reluctant to do an update, much less on top of the 2 I have declined.

I posted this last night but some how it did not make it to the forum. With the risk of messing up the computer and the unknowns of setting CEL codes, I decided to change from a kill switch to an alarm. When I got the truck the first thing I did was add 2 more horns in parallel with the stock ones, with their own power source thru a relay. I've designed a circuit that will energize these 2 extra horns when the ignition fuse box is energized and my alarm switch is closed. Bought a wireless switch today to turn the circuit on and off, so nothing will be in the cabin and the computer won't know about it. Not as good as a kill switch, but probably 80% of the benefit for 20% of the work and risk. My hood is already padlocked and all the components will be under the hood. With my limited electrical knowledge the horns will shut off when he turns the ignition off. When my electrical engineering buddy gets back from his motor home tour of the US later this month, I'll get his help to figure out a ratchet relay so the horn will stay on once it is triggered.

sorry I left this out, the truck is push button start with the fob in your pocket. jsdirt:. A VERY good point you make on starving the mechanical fuel pump. Had not thought of that. in initial post I referred to a starter "relay" in the engine room fuse box. It is actually a 30 amp circuit breaker with just 2 spades. It seems to be a strange rating though, the starter itself would be 100 amps or so, but a starter solenoid would not be anywhere near 30 amps. I could put a relay in that circuit and just pull the low amp relay coil circuit into the cabin. there is start interlock from the brake pedal light switch that would work, but it has 3-4 wires to it so again need the wiring diagram. For that matter, there are probably a dozen interlocks that have to give permission to start. the Aldata sub is a good idea, but surely someone has done this before.

Thanks, but I don't have access to the wiring diagrams (that I know of). I have the upfitter wiring diagrams but they don't cover these areas. I had already considered making a switch out of a headphone plug. Even considered converting one of the power plugs into a switch using a closed circuit male plug as the key. Today experimented with switching the circuit on the electronic e-brake, but the computer just releases it when you put it in drive. The truck has 2 fuel pumps, an electric in the tank and a mechanical driven booster under the intake manifold. The only fuel pump fuse is labeled "secondary fuel pump" which seems backwards. Forgot to mention the truck is keyless version. Keep the fobs in shoe polish tins, hood is locked, and obd2 port is in a lockbox. If I could figure out a kill switch then maybe my OCD could take a rest.

I have a 2020 GMC HD gas and want to install a kill switch to prevent it from starting. Having trouble finding the right fuse in the engine bay fuse panel to break. Initially I considered the starter solenoid but the only starter circuit there has a 30 amp relay. I could use that but really don't want to wire that many amps into the cabin. There are a couple of ECM fuses but I would assume killing those circuits would make the computer run in "learn" mode all the time. Can someone suggest the right circuit to break that won't do damage nor set off the CEL ?? Thanks.

The only way my 20 will lock while running is with fob. Internal lock and outside lock buttons are inoperable. Is there a setting for this in the truck settings in stereo screen?

I'm sure this is a dumb question, but why can't you simply wire the 2nd battery in parallel directly to original battery? If you connect new batt ground to the jumper connection just forward of original battery, the load on 2nd battery should go thru the load sensor (doughnut) inboard of the battery and connection.

I did something similar, but just removed one of the tail lights and tapped into the wiring to the rear bed light that shines inside the bed

How did you wire the winch into electrical system?. Is it still as simple as attaching straight to battery with appropriate circuit breaker and switch?

I have 2020 with similar. Last week I took 2 rolls of tape and stethascope and hit the interstate for some trial and error. I sealed the door/tow mirror interface with one wrap of electrical tape that got most of wind noise. Doesnt look as bad as it sounds. I've read some dealers are installing 2 gaskets there. I ordered some .6" and some .9" rubber o ring stock for permanent. Still had a whistle which I traced to where the vertical and angled line of front edge of driver side window meet. It was not a leak but turbulence. Rigged a 1"x1" piece of gorilla tape stuck to black triangle trim on outside so that tape just extends over that joint and past it about .5" These two things eliminated maybe 75% of noise.

That's why I bought a GMC. Well, that and the grill.

I may be wrong, but I thought the anti-syphon valve required since the '80's to prevent gas fires in a wreck made it impossible to steal gas this way.

We have a folding golf cart and 30' TT and travel at about 16,500 gross combined. It's fun to drive towing or solo. And I love the integrated brake controller, absolutely seamless.

The owner's manual says to wait 500 miles before towing, and to change oil before first tow. This is not under break in, but first paragraph under towing section. I have 8k travel trailer and load the truck to 9.3 k lbs when traveling. I just traded a 19 dmax for this 20 Gasser. It is plenty powerful for me, and more fun to drive than the dmax.

I know this is off topic but searching for this info and your discussion was close. Do you know where I can plug in for a small amount of "switch off" power??

Not meant as an insult, but have you tried changing the direction the vents blow? On mine, if I aim a vent all the way down it closes the damper for that vent.

TOMATO: here are pix of my horn additions, 2020 gmc double cab 2500 gas: The silver bolt next to the yellow wire in 2nd picture is an existing bolt on a bracket extending towards the engine on the rear inboard corner of the battery. Used a scrap 1"x1"x1/4" piece of aluminum angle and fastened the horn assembly to that one existing bolt. These are just Auto zone/Adv auto horns off the rack (they come this color). Nothing exotic but a very different tone (very loud beep) that makes the combination of the 4 horns more noticeable while not being a discord. I looked on Ebay for those 4 horn sets that used to come on cadilacs but they were pricey. I measured amps, looked at fuses, and decided I HAD to add a relay which just gets the hot right off the battery. The relay delay is not noticeable.