I have a 1999 rx300, with about 70,000 miles on it. I have been battling this problem for two years. My check engine light keeps coming on. I have taken it to the repair man several times and have had several things replaced on it, due to the codes that are being giving. I have replaced the solenoid sensors, the oxygen sensor, and replaced the cad. convertor (not lexus brand). All this due to the check engine light coming on. All of these problems happen in the winter. My car does sit outside, although I do let it warm up for about 15min. Even then it takes about 1 mile for it shift correctly I think into third gear (45-55 mph) I don't know if that has anything to do with the ck engine light. Every time I go to the repair man, they reset the light and within a wk in the winter time it comes back on. Now, when it hits spring and summer. I have no problems with the car. Yet, if I don't let it warm up, just a bit in the summer. It still will have shifting issues. Not bad though. Nothing like in the Winter. But no light! But it seems to be all in the winter time and cold air. Does anybody have any suggestions? Right now, I'm just driving it with the light on and not taking to the repair man. Any in site would be helpful

 

I know when Jiffy Lube changed the oil, they invariably pulled the emissions equipment hose out when they checked the air filter, causing the CEL to illuminate.

Yeah, I know, the first problem was using a quick oil change place...

TC

 

it appears that about 90% of check engine lights come on from high or low oxygen from o2 sensors. There are two o2 sensors a upstream and a downstream. These can be tested as one is normally price and the other high priced. You can try replacing the upstream one or take it back to your mechanic and have them tested. You also want to check battery voltage, corroded battery terminals and broken wires