TennLexus1

Hi all, great forum here, I'm new and just checking out all the interesting and helpful threads!

I have a 99 RX300 with 127,000 miles on it. Recently, the check engine light came on, but everything ran fine. Then the light started blinking and car ran very bad, and wouldn't shift into overdrive.

Took it to the dealer and they replaced the ignition coil. It's running great now, but still not shifting to OD.

The other codes that popped up were thermostat and the air/fuel sensor. I was wondering if either of these things could cause the OD problem. I know when it's cold, it will take a while for the OD to kick in, so I'm guessing that maybe it's the thermostat? How hard would that be to change myself?

Thanks in advance, any help would be great!

lexus114

Did you replace the a/f sensor yet?(you said that was one of the codes) that will throw everything off if it is bad.So Im assuming your check engine light is still on correct?

TennLexus1

Hi, thanks for replying. I have NOT changed the a/f sensor yet. It's $400 (at Toyota dealer), trying to put that off if I can...

Yes, the check engine light is on. Is the a/f sensor something that I could do myself?

Thanks, Dirk

lexus114

Well,are you some what mechanically inclined?If so,yeah you can do it,but pray it is the one on bank 2 witch I believe is the sensor on the front manifold.(radiator side)if it is the rear bank,1 I believe you would be best off taking it to your mechanic.The answer to your other question is,when you have a cel on,it will not shift to overdrive.Oh,make sure you get an A/F sensor not an 02 sensor.Their is an 02 sensor post cat.(only one on vehicle) but rarely goes bad.

TennLexus1

I'm fairly mechanically inclined.. I get more mech inclined the more broke I am, lol!

When the cel originally came on, the OD was still working fine, but I'm not sure what code the cel was referring to.

What about the thermostat, how hard is that to replace? Are there any good sites with repair help/diagrams that you know of?

Thanks SOOOO much for your help!

lexus114

From what I understand tenn,the thermostat is a real bear to replace + rarely goes bad.Does it show on the temp. guage that its running hot?If not dont worry about the stat.Also,the delayed shifting when vehicle is cold is quite normal.Mercedes claims they do that to warm up the cars catyletic converters quicker,(so it gets into closed loop sooner)I dont know if that is lexus`s reasoning for this or not.(btw) closed loop is when the ecm has full control of emissions.

TennLexus1

114, No it's not running hot at all. About in the middle of the gauge, where it's always been. I guess my therory is that if there is a delayed shifting when cold, so the catyletic converter kicks in quicker, what tells it that's it's ready? If not the themostat, maybe a tempeture sensor?

The dealer wants $200 to change the themo, and $400 to replace the a/f sensor. Just trying to figure out which is more likely, cause i'm a little poor right now with $4 gas. The OD not kicking in has dropped my mileage from 21-22 to 14-15 MPG - OUCH!

lexus114

Seriously,just replace your a/f sensor,make sure no other codes present,clear ecm,should be good to go.I will mention one more thing,try to replace the other A/F sensor before too long,as it will probably go now too.(their notorious for that)Same thing with knock sensors,they should be replaced in pairs too.

Rxsmarx

Ever find a fix for this ? Mine is not shifting in to overdrive at the moment.

lexus114

Overdrive and a check engine light go pretty much hand in hand.In other words if your cel is on,you are more than likely not going to have overdrive.Why this happens,probably because it goes into what is called a limp home mode.(Not meant to be driven in this condition)Just to get you home,or to a shop.

bchehab

Hi.

I had a similar case where I replaced 2 coils, and the car didn't shift to OD. I removed the battery cable for 10 minutes to reset the ECU. and now it is working fine. I don't know what is the relation but it is working.

Regards

lexus114

Because you reset the computer.