Okay, figured out what's wrong...now what??

The only way to do it is get the factory service manual and follow the flow charts to diagnose the problem. I would guess the problem with the O2 sensor is causing the lean code. The O2 is critical to the fuel mixture and without it working right you'll have problems. If you are a little bit mechanically inclined the manuals will quickly pay for themselves. If not, then find a good mechanic other than the dealer. They will probably still need the manuals unless they know the supra inside out. Good luck.

You need a new 02 sensor. Sensor 1 bank 1 means the closest one to the block(if you had a "V" engine-bank 1 refers to the bank with the #1 cyl.) Generally one code will be generated and the ecu will sometimes spit out all codes app. to that area. Although I have spent little time working on mk4's I would assume there is one sensor before the cat and one after-replace the one before. They are high dollar-guessing I would say 150.00. I would definitly start there-there may be other problems withen the heater circuit itself-but I have never seen this.hope this helps. Remember you'll need to clear the codes after the repair to reset the light-just pull the efi fuse for appox. 30 secs.

Thanks for the advice guys. I've added a bit more fuel to the car via the VPC (it's now at +2 clicks on the gain, approximately +4%) and this has seemed to have helped...no stalling and no check engine light...yet. I'll definately go ahead and change the O2 sensor. Question, how hard is it to change the sensor?? Is it something I can do or is it something I should leave to the pros??...Darshana S...

Supraman16 said:

Thanks for the advice guys. I've added a bit more fuel to the car via the VPC (it's now at +2 clicks on the gain, approximately +4%) and this has seemed to have helped...no stalling and no check engine light...yet. I'll definately go ahead and change the O2 sensor. Question, how hard is it to change the sensor?? Is it something I can do or is it something I should leave to the pros??...Darshana S...

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It is a pretty stright forward job on most toyotas-I can't recall ever doing one on a mk4 but they should be all about the same. Just unplug the sensor, unscrew it if it is a screw in type(need a 22mm wrench) or unbolt it if it bolts in(12mm) pull it out and drop in the new one and reverse the process and reset the ecu. Some toyotas the wire runs into the cabin and you have to remove the pass seat to unplug it, but I doubt the mk4 is like that.Remember to get the front one if there is 2-they are most likely different. I like to replace them both anyway-if you have the cash do it that way. I'm sure someone who has done this on a mk4 will chime in and help out more with the details. This is one of those jobs were you can do it yourself and really not have to worry about messing anything up-theres really not much that can go wrong(disclaimer-i didn't just say that if you somehow mess anything up and you can't sue me ) I'd give it a shot-makes you feel good when you do it yourself