POS_miniracer

Another couple of questions for you all. Does disconnecting & reconnecting the battery actually clear the codes or just remove the check engine light temporarily? The reason I ask is I did this in order to see if the car would become unlocked out of OD and it seemed to work. The check engine light did however return several miles later but the car/trans stayed fully functional. I suspect however that it wouldn't lock me out while going down the road and also suspect that if I attempted to drive it again after turning the car off it would probably be locked out again. I have not addressed the O2 sensor issue yet but did replace the coil on the #1 cylinder. While doing so I had the battery disconnected and afterward took it for a test drive to see if I could trigger the CEL to come back on and as of yet it hasn't. Usually I'd just have to drive it aggressively to make that happen and I'm pretty sure I replicated what would usually cause it to come back on but so far it's staying off. Another question I have is (and I know this is hard to pin down) roughly how many miles is the O2 sensor that's located just in front of the muffler usually good for? EDIT: Got the light to come back on. But at least this time when I scan it I'm only getting the one code now (PO171)which lists as one of it's possible causes the HO2S(heated oxygen sensor)which I'm hoping is the one hanging from in front of the muffler.

Thanks, I'll try that.

Thank you both for the fast replies. A good friend of mine owns a trans shop that I actually once worked in so I'm going to take it over there to use the good Snap On code reader and I'll also be able to reset it at the same time to see if that makes any difference. It's about 10 miles round trip mostly in a 40 mph zone so I should be okay driving it that far. When it happened initially I had to drive it home 40 miles down the highway at 50 mph trying not to get run over. The odd thing about the codes is that the thing ran perfectly smooth the whole time. I was a motorcycle mechanic for 14 years and I'd like to think I'd recognize a misfire when I feel one and it doesn't at all feel like there's one present. I'm getting about 19 mpg on average between city and highway which from what I've read seems to be the norm. As for the catalytic convertor being clogged I suppose it's possible being 12 years old, and the previous owner did do a lot of short trips but it revs out freely and goes down the road like a champ (until this happened) and the O2 sensor is behind the convertor. Maybe the muffler is clogged? Again, it doesn't run like there's an issue though. Either way it looks like I'll be pulling the exhaust off anyway in order to get the broken bolts for the O2 sensor out so I'll at least be able to hear if there's any rot rattling around in there. Not a great test but at least if there's anything really obvious I should be able to detect it. It seems to be flowing normally out the tail pipe even with the hole left by the missing O2 sensor. So I guess the plan is plugs, wires and O2 sensor then I'll reset the computer and see what happens.

I have a 1999 RX300 AWD that just recently stopped shifting into overdrive. Here's a little history. I bought the car about a year ago with 52K miles and soon after the CEL came on with these two codes PO446 & PO171 The car was elderly driven and I suspected that the first time I stood on the gas I fouled the O2 sensor so I disconnected the battery and the light went out and stayed out for quite some time. More recently the CEL came back on again and I pretty much ignored it until about a week ago when I developed an exhaust leak. To my surprise I found that the O2 sensor mounted to the front of the muffler had blown of shearing the bolts off with it. So I ordered an O2 sensor while I tried to formulate a plan to avoid replacing an otherwise good and fairly expensive muffler. Three days later the car stopped shifting into overdrive. I've been reading around about the issue and see many posts regarding a bad knock sensor code so I went down to the local Autozone to have the car scanned but I get no such code. I do have the same PO171 (no mention of the previous PO446) and I also get PO300 and PO301. I'm assuming the PO171 is the O2 sensor that now dangles under the car? The PO300 and PO301 indicate misfire detected-random cylinders (PO300) and misfire cyl number 1 (PO301) although the car shows no signs of misfiring whatsoever, But the car has about 69K miles on it now so I figure it's time for plugs and wires anyway. So my questions are, is there any chance curing the existing codes might also cure my OD problem? If not, will it damage the car to drive it while locked out of OD?

Thank you for that. It tells me exactly what I need as far as testing those components.

Hello everyone. I just purchased my father's '99 RX300 and on the way home (250 mile trip) the check engine light came on. I took it to Autozone to have it scanned and it came up with two codes: PO446 aaEVAP system vent control circuit Probable cause aa1-Open or short circuit condition aa2-Poor electrical connection aa3-Faulty vent control selenoid. The other code is PO171 aaSystem too lean- bank 1 (Cylinder number 1 denotes bank 1) Probable cause aa1-Lean Air/Fuel ratio-fuel injector or vacuum leak aa2-MAF sensor concern aa3-ECI sensor fault aa4-Faulty HO2S (heated oxygen sensor) Now a little background. Original owner now 70 years old. Car has 52K miles mostly city and has probably only seen passing gear a dozen times in it's life and probably never over 60 mph. Always fueled with regular octane, ECT always in normal position. Never a single issue or repair outside normal tires, brakes and routine service. So that's how it was driven all it's life. Now I get in it and drive it like I stole it all the way home in ECT Power, in passing gear almost as much as it wasn't, held 85 mph for several miles and made the 250 mile trip in 3 1/2 hours including stopping to let the dog out for 15-20 minutes, all in holiday traffic. Just to give you an idea of how I drove it as opposed to what it had been used to. Not at all advocating my driving style. It was actually when I stopped to walk the dog that I noticed the light stayed on when I got back on the road again. So my question is where do I start first? My gut tells me I blew 10 years of carbon build up out the exhaust and affected the O2 sensor but I've been doing some reading here and understand there are 2? and that it's not uncommon to have MAF issues with these. Oh, and I managed to keep a 21 mpg average as opposed to my fathers 23 hwy. Any suggestions (besides the obvious "slow down") would be much appreciated. Thank you all in advance.