Yet Another Rx300 That Won't Shift Into Od

[POS_miniracer]

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?

[Filehorse]

Interestingly enough, there is an excellent chance that one or more of those P codes is causing your transmission to not shift into Overdrive. Twice I have had an ignition coil to fail which then causes the Check Engine light to appear. For the first 20-30 miles there was no problem aside from the reduced power and the rough idle with only 5 out of 6 cylinders firing. However, after that 20-30 mile period the transmission would refuse to shift into overdrive. If nothing else, it will force you to get it to dealer or a good independent shop to get the codes checked out. Once the coil(s) were replaced the codes cleared and the transmission once again resumed normal operation including Overdrive. This happened to me twice so I know it wasn't just an odd occurrence. I'd guess that once you get your known problems cleared up and the codes cleared, you'll find the drive system will magically resume normal Overdrive operation.

As to long-term damage to the transmission operating it without overdrive, I'm sure some short time period of limited operation won't hurt anything but it's not something I would want to keep doing on a long-term basis. I'd be real careful about not getting this taken care of in the near term. I had my transmission rebuilt earlier this year for the trifling sum of $3200 and operating at a much higher RPM vs. road speed cannot be a good thing for a transmission that is a notoriously weak link anyway.

Caveat emptor.

Let us know what you find out.

[blk_on_blk]

It's true that when the knock sensor is triggered, the ECU will fully !Removed! the engine and lock you out of OD in the transmission, but I doubt that's the only code that does that. A misfire code may do the same thing. It's a protective mode so you don't damage anything, although it does make you run without overdrive and with the engine timing fully retarded. Add that to the hanging O2 sensor and I wouldn't drive it until the underlying problem gets resolved.

I would advise you to get a cheap code reader/resetter off eBay or somewhere. That way you can reset the ECU and see if your overdrive comes back. That's a good indicator that your getting a code that's disabling your OD (and most likely retarding the engine timing).

I would also speculate your may have blown your O2 sensor and be getting misfire codes possibly due to a clogged catalytic converter. When they plug, you get all sorts of back pressure in the combustion system. It could hold in unspent residual fuel (due to the retarded timing) and be igniting within the cylinder throughout the compression cycle, causing the misfires. If that is the cause, I would definitely not drive the vehicle until it's fixed.

With the engine revved, can you feel much exhaust flow coming out the tailpipe? No or low flow would be a good indicator of a plugged cat.

Lastly, the P0446 code is often a 'phantom code' in the 1999 RX300. I've had ours come on randomly for years... sometimes 6-9 months between it tripping. I just reset it and it rarely comes back.

BTW, I would get that O2 sensor fixed before trying to troubleshoot anything further. Hard to isolate the cause of something when you have a known issue contributing.

[POS_miniracer]

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.

[lenore]

I would not go with plugs, they are historically good for an easy 120k miles. They are iridium, and even at 120k miles look like new. If the (02 sensor) is repaired and you recheck codes, and still get the p0300 etc than you have a bad coil pack, you can swap them and see if the code changes to determine if that is the culprit. if it becomes a code p0302 etc, than you know that is a bad coil. The coils on the back (firewall) side are a pain to get to, but the front ones are real easy. There are no wires, as the coils rest right on top of the plugs. I always put a little dielectric grease around the cap that plugs onto the plug as that will prevent moisture buildup and corrosion. good luck.

[POS_miniracer]

Thanks, I'll try that.

[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.

Edited December 27, 2011 by POS_miniracer

[Shifflett]

I have a 2000 lexus rx300 it will shift into overdrive but after it sits for a day it won't shift into overdrive anyone know why.