davester

It could be something similar to the GMT800 series, in that it's powered two separate ways, one way goes to the switch right at the light, and a second way via the bcm, where the switch on the dash, and the doors will go through to turn the light on. For my truck, the TBC2 fuse, going to the bcm, would blow, and it would take out the dome light and backup lights. You could try checking that all your fuses are still good?

Does the electronic indicator in the instrument panel change to indicate what gear you've selected as you move the shift lever?

Yes, it changes a LOT. For any given RPM, you will have a different throttle plate angle (so, different amount of air through the engine), amount of fuel injected, and spark advance, between open-loop and closed-loop. You can't compare the two and go "Oh, it's the cat that's bad." And even comparing open loop mode, with the O2 sensor port unplugged vs plugged, then what? What do you use to measure the power output? Seat of your pants? You might as well just tell the guy to just buy new cats and hope they fix the problem, and if not, you'll tell him to buy more parts to throw at the truck until it's fixed. The backpressure test is -easy -cheap -accurate -fast -the defined way to test for this specific problem and your idea is to go "screw that, I'll make up my own testing procedure".

Do you mean that you -can't move the shift lever when the ignition key is in the "run" position, but you can when it is in the "Accessory" position -can move the shift lever, but the truck doesn't move in any gear with the engine running

No, it's not just an "air pump". It becomes an apples to oranges comparison. The engine is getting a different amount of fuel at any given rpm, so comparing how the engine runs/feels when driving with the O2 sensors out vs installed, tells you nothing about whether or not the cats are plugged. If the engine runs better with them out, it might be the cats, but it could also be any number of other things that are making the engine not work right with the O2 sensors installed, that may or may not generate odbii codes. Testing the backpressure is literally THE test of whether or not the cats are plugged. It's a simple, not particularly expensive test to do. Your idea tells you nothing about whether or not the cats are plugged.

Actually, that's not really a valid test, as the ECM stays in open-loop mode, basically running the engine completely differently than with the O2 sensors installed.

I know, the text is ambiguous, which is why I copied it as it was written in the manual, including how it was split up on multiple lines. I don't know for sure, but I would say it's more likely the 3 psi is the max, as I don't think the 6.0L got a way bigger cat. so the backpressure could be that much lower.

From my '04 Sierra full-service manual, for testing if the exhaust is restricted, you test the pressure at the upstream and downstream O2 ports (removing the air check value/O2 sensors, and screwing in a pressure gauge in their place), start the engine and hold the speed steady at 2000 rpm. It says it's restricted if it exceeds the specified value: 20 kPa (3psi) If equipped with a 4.8L, 5.3L, or 6.0L - 3.4 kPa (0.5 psi) [the above is exactly as printed in the f.s.m.]

You can either take the vin to a dealer, and ask for a build sheet (they may or may not give you one, and may or may not charge you for it), or you can decode the RPO codes on the sticker in your glovebox. Those 3-digit codes detail what options GM installed in your truck. It's useful to keep this list handy when buying parts for the truck as well, as some parts vary depending on what options your truck has (brakes, transmission oil lines, alternator are just a few things that vary depending on what options you have).

I just use Costco batteries now. I've spent more on batteries, but I haven't found it to be worthwhile (either for warranty or for lasting that much longer to be cost effective). I live in Alberta, so we get both heat in the summer +35C and the cold -40C, so the battery does get stressed for me. It's also a daily driver work truck, where I make about 10 stops a day during the summer and 30 stops a day in the winter.

No, it's on the rear-facing part of the TC. I would suggest using google images for gm pump rub, to see pics of where the hole happens, if you want to see it.

Just certain years, namely, the GMT800 models, from '99 to '07. Later years ('05 or '06 maybe?), they added a little steel clip the case, to try to remedy the problem cheaply, but the clip also has a tendency to break off, so it basically just takes a little longer for the problem to happen. And there's no "sign" of having TC pump rub until it's rubbed a hole in the case and you see fluid on the underside of the vehicle. You don't typically see a puddle on the ground under your truck because of this problem, as the hole appears above the fill level, so it only comes out while you are driving. I wouldn't count on it being mentioned to you when the truck is serviced, as the hole can happen at anytime, it generally doesn't leave a lot of fluid on or under the truck, and the TC dies pretty quickly once the fluid is gone. I would suggest figuring out when your truck can be down for a day or two, and get a pump rub plate installed at that time. It doesn't take a lot of time to do, but (IMHO) it's better to do it when it's convenient for you and cheap, rather than after the hole appears, the fluid comes out, and you have to replace a bunch of other parts in the TC, or just replace the whole TC, right when you need to use the truck.

Yeah, level surface, put on the parking brake, with the engine off, switch gear lever to drive and the DRL lights should be on. I actually bought replacement DRL lights twice (and returned them) thinking they didn't work and forgetting the truck needs to be drive for them to come on.

The "gasket" between the exhaust manifold and the exhaust pipe is a metal ring that goes in the slot in the manifold (might be in the exhaust pipe flange, it's been awhile since I did it). The ring is slightly oversized, so it crushes a bit when the two parts are bolted together.

My '04 Sierra 6.0l gas 3500 starts fine, without being plugged in, at -25C/-13F. Older vehicles with carbs had more problems starting when cold, fuel injection made a big difference with cold starts. Now it's more about how good the battery is, that it can crank the engine when it's really cold out. Plugging in the truck does help with this as well, as it's easier to turn over the engine when it's warmer. And plugging it in also helps with getting the cab heated up faster...