TillBeam

My 99 RX300 (120,000) miles will not shift into its fourth gear. It runs at 5,000 rpm at 60mph. The transmission guy said the transmission was working well and that the problem was the computer putting the vehicle in “limp” mode because of the check engine light. The check engine light called for the replacement of the MAF sensor, which satisfied the code. The check engine light then lit up again citing an malfunction in the knock sensor 2 circuit. When I clear the code it drives fine until it is time to shift into the fourth gear, then the light turns back on and the vehicle remains in its 3rd gear.

Furthermore, the ABS light has always been on (since I bought the car at 90,000 miles). It never bothered me before because I would rather drive without ABS. The mechanic checked the reason for that code and claimed that there was a problem with the ECM module and one of the speed sensors on one of the tires. He expressed hesitation regarding his ability to work on such an issue. He thought that it is absolutely possible that the failure of the sensor to recognize the speed would prevent the vehicle from shifting into its final gear, but he knew that the best he could do is to plug in a new ECM module and see what happens. He recommended that I talk to a Lexus dealership, who suggested that I bring the vehicle in (at a minimum $98). I hate the idea of taking the car to a dealership 80 miles away, but I do want the problem fixed. Has anyone seen anything like this? What should I do?

hypervish

Welcome to Club Lexus!

Once you change the knock sensor, overdrive will work again!

S76b

This is similar to the issue that has recently come up on my 2000 RX300 with 159,000 miles.
THe check engine light came on and now the transmission seems to be stuck in 3rd gear.The engine runs at 3500 rpm at 55 mph. Normally, it runs at 3000 at 70 mph.
Could this be the knock sensor as well?

hypervish

Only way to be sure is to check the codes and see which one it is.

BLH

I am new to this forum. I just purchased a 2002 RX 300 with 104K miles. I noticed on the drive home that it was not going into overdrive. I pulled over finally and shut the vehicle off. When I restarted and pulled out it went to working fine, going in and out of overdrive properly. That was only 6 days ago. Since then it has gone out of overdrive about three more times. Each time once I stop the vehicle (turn off the engine) and restart it seems to work fine for quite a while.

It does not have a check engine light, though I have not yet had it scanned for latent codes. Since it has been on a used lot for a while I assume the battery may have died killing any stored codes anyway.

I appreciate any advice.

I have this posted as well as its own thread.

Bobster999

A quick forum search will give you the answer. IMO this is the dumbest thing Lexus has ever done. Going in limp mode because of a knock sensor. How can that possibly be helpful to the owner? All it does is add wear on your engine by running higher rpms and use much more gas until you spend big money to fix it.

carguy07

Helps avoid those pesky holes.

AnthonyMtz

My dad has a 2001 rx300 and did that hack were yyou tap the wire into the other knock sensor and it worked the car runs great he's had it on there for almost 2 years

Bobster999

mine still runs great also. and i still only run unleaded gas @ 87 Oct

Bobster999

I certainly know what a knock sensor is for.
Let me try and explain myself better since you didnt pick up what i meant.
By losing one bank sensor, the PCM now removes the Overdrive, which cause the vehicle to ref even higher rpms. How is that helpful?
How about if the radiator developes a pin hole, lets add a breakaway valve so all of the fluid will spill out faster.
Or if the fuel gets low, lets make the windows inop.
I dont care what their reason was, you cant convince me its rational and in the best interest of the consumer.

salimshah

Need to differentiate between sensor going bad and giving a false reading vs actual pre-ignition happening (knock). So when actual preignition is happening, the solution is to increase the rpm. To increase the rpm you disable the top gear.

Regarding what is beneficial to the owner, well that is not the purpose of emission standards. At least not directly.



Salim

matts6887

I hear ya on the 87 gas thing. I see no reason to use premium unless there was a sticker on the tank lid that said ya had to. But since there isnt i said the heck with it and have been using 87.

Nick26

My problem like this was solved by replacing both knock sensors. Also improved gas mileage!
QUOTE=TillBeam;8033505]My 99 RX300 (120,000) miles will not shift into its fourth gear. It runs at 5,000 rpm at 60mph. The transmission guy said the transmission was working well and that the problem was the computer putting the vehicle in “limp” mode because of the check engine light. The check engine light called for the replacement of the MAF sensor, which satisfied the code. The check engine light then lit up again citing an malfunction in the knock sensor 2 circuit. When I clear the code it drives fine until it is time to shift into the fourth gear, then the light turns back on and the vehicle remains in its 3rd gear.

Furthermore, the ABS light has always been on (since I bought the car at 90,000 miles). It never bothered me before because I would rather drive without ABS. The mechanic checked the reason for that code and claimed that there was a problem with the ECM module and one of the speed sensors on one of the tires. He expressed hesitation regarding his ability to work on such an issue. He thought that it is absolutely possible that the failure of the sensor to recognize the speed would prevent the vehicle from shifting into its final gear, but he knew that the best he could do is to plug in a new ECM module and see what happens. He recommended that I talk to a Lexus dealership, who suggested that I bring the vehicle in (at a minimum $98). I hate the idea of taking the car to a dealership 80 miles away, but I do want the problem fixed. Has anyone seen anything like this? What should I do?[/QUOTE]

AnthonyMtz

[QUOTE=Bo bster999;8899890]mine still runs great also. and i still only run unleaded gas @ 87 Oct[/QUOTE

yea for some reason his 01 with 200k miles gets 400 miles to a tank of 87 octane wile my 2002 with 175k that I always run 93 octane on can barely average 220 a tank...and I get 12 mpg no CEL Lights or nothing...still can't figure out the damn problem...I burn through gas...LITERALLY

kalali

[QUOTE=AnthonyMtz;8917369]Switch to regular 87 and see if it makes a difference.