I have a 1999 RX300 AWD with approx. 152K miles. I am the original owner and have been fairly religious about getting the vehicle serviced per the guidelines, typically at a Lexus dealership. We have had very few problems with this vehicle.

Just recently, the vehicle has started failing to upshift as it would have normally. The AT shifts normally until I reach an expected shift in the 40-50 MPH range. This shift never happens which results in very high RPMs if taken out on the highway (which I am now avoiding). I have tried both with overdrive on and off with the same results.

I do have a check engine light on, so could my problem be related to a sensor? When the light first appeared, we had it checked at the dealer and it was not related to the transmission but we did not opt to repair the problem (emissions related IIRC). As to the transmission fluid, it was replaced approximately 6 months ago (at a reputable service shop but not the dealer) and I have again had it replaced due to this problem to no avail.

Appreciate any advice/help.

DL

 

By design, your trans will not shift into high gear with a CEL. You need to get the code read and fix the problem causing the CEL and then your trans will shift into high gear again.
Disconnect your battery negative cable or pull the EFI fuse to reset the CEL. Your car will then shift normally until the CEL returns.

 

Welcome to the Club.

If you bring me the number of the CEL, I can probably help you track down the issues.

I would also check the fluid level as well. You are right that you should have a shift right around 40 mph.

 

Could be a failing 3-4 shift solenoid.
Also if the ecu doesn't see normal operating temp. met. It won't upshift to
4th.
But as Lexmex sugg. Check for the obvious first. Fluid level and the code.

 

Thanks. Fluid levels are fine, just had a drain and fill done.

I got the CEL codes checked and had several:

300
301
303
305
125
1135

Not sure if any of those are related to the transmission issue but there you have it.

DL

 

You have misfire codes only on Bank 1 (firewall side)
P1135--B1 A/F sensor
P0125--Insufficient Coolant temp for closed loop.< this might be your problem for shifting issues.
Open loop is when it's in warm up mode. Once the ecu gets a signal from the CT sensor that it's warmed up enough it switches to Closed loop operation.
The ecu is stuck in open loop and won't allow the trans to shift to 4th.
How's your gas mileage?

I would first diagnose the coolant temp sensor before going further on your misfire codes. You could still have a problem on you A/F on B1.

 

Read your post, and sure enough, I have the exact same problem with same model ('99 AWD). CEL has been on for some time, and when I had it checked, there was the good ole O2 sensor code (don't remember which one). However, lately, on rare occasion, when starting in 1st gear from a stop, tranny won't engage. I will shift to "Park", then back in "Drive", and everything OK until 4th gear. Trans. fluid has never been changed that I know of & I have about 94K on it. Plan to change fluid, pan gasket & filter this weekend. Also, I know the subject has been beaten to death, but what is the skinny on TypeT-IV versus Amsoil? Local ripoff Toyota dealer wants $7.50/qt. of T-IV.

 

My Toyota dealer sells the Type-IV ATF for $4.70 a quart, while my Lexus dealer wants $7.99. So shop around. I use it exclusively in my RX300 and have no tranny issue after 120K miles through Colorado mountain roads.

Amsoil ATF is a one-for-all (Amsoil calls it universal) fluid that is designed to be the middle ground for most vehicles in the market today. Visit the Amsoil website to read its amazing claims and its long list of compatible vehicles, then decide for yourself. Price can vary wildly among the "independent distributors" that troll Internet auto forums.

 

Thanks Harrier: Shopped 3 dealers locally & found price range from $4.98/qt. to $7.25/qt.. Purchased 8 qts. & now ready to Git-R-Done.

 

May be too much. Remember the fluid in the Torque converter stays.


Also measure what comes out .. getting a good read is very hard.


Salim

 

Well dudes- bad news- when I purchased tranny kit (filter & gasket) I had codes read due to CEL on for a long time now. Came up with P0330 & P0171. From other posts, it looks like this is knock sensor problem which is causing the lean system code and prevents engine from shifting into OD.

Now the big ? DIY for $400-$500 & a pair of cajones, or dealer $1000-$1200. Are there any detailed posts on how to replace, or should I purchase manual? If manual, what is best? Also, does left engine bracket have to be removed? If so, what can I use to support engine?

From what I gather, I will need both knock sensors (I'm pretty sure they're the same part), coolant bypass hose, intake manifold gasket kit & 28mm socket. Anything else?

 

Here it is:
http://us.lexusownersclub.com/forums...or+replacement

 

THANKS thomas1- didn't see that post when I did a search. Will keep y'all posted.

 

Just wanted to be absolutely certain that replacement parts (knock sensors, intake manifold gasket set, bypass hose, & wiring harness for sensors) are the same for 1999 RX300 AWD as they are for 2000 model. Also, I found OEM knock sensors, therefore, do I still have to replace wire harness?

 

There should be no difference between 1999 and 2000. Occasionally, I have seen Lexus upgrade part numbers over the years, but they are always compatible across the 99-03 model years sold in North America. Wire harness should be replaced on this item.