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Knock Sensor


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Hi, I have a 2000 RX300 with less than 80K miles on it. Like a dope, when the gas prices got really high i put regular gas in the car. after a few months with a lot of knocking i thought i'd better go back to premium. the knocking has stopped and mileage has improved. BUt now i have the check engine light on. while driving at around 60mph my rpms are at 4000 and it doesn't feel like it going into fourth gear. My mechanic, who has the same car, changed his tranny and still had the check engine light on. he said that after he changed his knock sensors the light finally went off and suggested thats what i do rather than go directly to the tranny. the code does come up as the sensor.

Does anyone out there know if replacing the knock sensors will actually make my car shift into gear? He quoted me $650, which i think is reasonable and will also have my spark plugs changed out while he's in there. but has anyone else had this problem?


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How big is the shade tree your mechanic is operating under? Surely this guy can't be a professional? Does he know how to read and interpret stored error codes? Here is a list for the LS400 and the list is similar for an RX: http://www.lexls.com/tutorials/intro/codereading.html

In the 260,000+ miles I've driven Lexus cars, I've never had a mechanic "guess" at the cause of a problem -- that's why they follow diagnostic procedures and use specialized equipment.

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From your post it sounds like your mechanic has already read your code and it points to a knock sensor. When your CEL is on from certain codes (knock sensor code is one of them), the ECU prevents the tranny from shifting into 4th. This is by design. Change the knock sensors, get rid of the CEL and it will shift again.

On another note, you did not cause your problem using regular. That is all the RX requires. My guess is your knock sensor was going bad and preimum was needed to prevent knocking. Try regular again once you get your knock sensors replaced.

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