For some reason, when I'm in 3rd gear on the freeway and I hit 4000 rpm's for any length of time, my check engine light comes on. However, it does not come on when I'm in 1st or 2nd gear @ 4000 rpm. I'm just wondering what it is about 3rd gear, or the speed I'm at that causes the light to come on. It also comes on during cool weather in the morning/night when I accelerate up to freeway speed. Maybe that has something to do with my O2 sensor? The light will go off as soon as I upshift to O/D or let off the gas. These are the only times my check engine light have come on as long as I've owned the truck and I just want to make sure everything's ok. Maybe someone has seen something similar.

 

That does sound agravating. But I wouldn't have a clue to start looking other than to pull your codes and see if that gives you any ideas. But one quick question.......what the heck are you doing driving 4000rpm in direct gear?!!!! In my truck, that is about 100mph. Just curious, cuz I can't see myself driving 100 down the interstate in my lifted truck for extended periods of time. Does your truck has a built in rev limiter in certain gears maybe?

 

Yeah, next time I have access to a code reader I'll check it out.

Regarding my speed, I'm not sure but I'm probably doing somewhere around 95 mph at that point. Well, it's not often that I exceed 4000 rpm in 3rd gear, but hey, when I see my brother pulling up behind me in his brand new Z71 on the freeway, I've got to do my best to give him a run for his money The only thing is, I'm pretty sure I can safely take my rpm's up to 4500, so it's frustrating to have to stop at 4000. I've topped 100 before, back when my check engine light wouldn't come on at 4000 rpm. Don't get me wrong though, I don't like to stay there long, I'm too worried about getting a ticket!!!

 

I'm guessing it has something to do with your EGR staying open, but that really is just a guess. You need to post the codes, and we can go from there.



Take care,
~Chris

 

Man, that is down the line a ways for things I worry about going that speed. Actually, im probably more worried about a wheel bearing going out, then a tire blow out, then finally, the pigs. But I have plenty of roads around here that I MAYBE see a cop on once a year.

The EGR does sound like something to check on, The EGR is supposed to be closes at WOT, so its possibly sticking open.