Sometimes my car will shift into overdrive and sometimes it wont.Does anyone know what it could be?I just bought this car and im so in live with it.Its a 99 rx 300.i pulled the dipstick on the tranny and it didnt smell burnt.Any suggestions would help thnxQUOTE][/QUOTE]t

 

From what I've read, a common reason for not shifting into overdrive is not a transmission fault, but rather a Check-Engine-Light (CEL)-type fault condition. I suggest you purchase or borrow a OBD-II (2nd generation on-board-diagnostics) code reader and see if their are any codes showing. If so, I think you need to focus on clearing the conditions that are generating the OBDII codes.

 

My guess is a knock sensor

 

Does it have a CEL? If so, get it read and post back here.

 

Can the 0xygen sensor below the cat cause an overdrive issue?

 

I got code p0420.Whats that mean?

 

No. That's purely an emissions sensor.

 

Catalyst System Efficiency Below Threshold.

To make a long story short, it doesn't necessarily mean anything is wrong with the O2 sensor or the catalytic converter. On particularly hot days in Mexico City I used to see people get this code at my uncle's shop (it's a low oxygen environment) and that can really screw up a/f ratios especially when going up hill in places. Try resetting it via the code reader and see if it comes back. Second time, pull the battery cables. If it's still coming back at that point, the first place I'd put my finger on is replacing the O2 sensor itself (these cats generally don't go bad running U.S. fuel), but the O2 sensor can. There's a DIY that I did on this sensor, https://www.clublexus.com/forums/rx-...sor-2-diy.html

 

X2, on doing the sensor first if the code comes back.

I had that code, and eventually replaced the 02 sensor behind the cat, and the sign hasn't come back ever.

 

I tried replacing 02 sensor behind cat and one of the studds busted off so now im stuck until i get some xtra cash to take it to the shop and have it drilled out.ugh

 

You have a picture of this?

 

I'm having same problem and having the knock sensors replaced.

 

Replaced both knock sensors and wire harness and over drive and shifting is all good now. Thank god it wasn't the transmission.