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Lexus RX behaving poorly

I have a 2000 Lexus RX 300 with 65K which has recently had its check engine light go on. Like a good owner, I took it to the local Lexus dealer where they promptly told me it was a failed knock sensor, costing $820 to repair. I agreed to the fix only to have the check engine light go on again 2 days later. Back to the dealer, and this time they read a code of the second failed knock sensor (on the other side of the engine) and an air/fuel sensor. They wanted $1100 to repair both, saying there were no assurances that this was indeed the problem. Both times the check engine went on, it was the exact distance from our house in nearly the same spot, both times in the morning at about 50 degrees, at about half a tank of gas. Is there something else going on here, or should I keep replacing sensors until I’m in the poor house? I suspect the car might not be getting enough fuel? In any case, there car has not been running rough as a result of any of this, just check engine lights going off. Please help!

Not to burst your bubble however your Lexus is a glorified overgrown Camry v6 which any versed mechanic can work on given its commonality. You won’t find a beautiful wait room or free loaner and nice coffee, but any decent independent can work on your vehicle.

They are wonderful vehicles just find a good mechanic, ask friends, family, or neighbors etc.

They are pretty proud of their knock sensors. A well-known auto parts supplier’s web site shows the OEM knock sensor for $204 and aftermarket for $189. They do get a mark-up (100% ?) so maybe it is hard to get to and took them 3 hours at $200/hour to get to. Did they break out parts and labor?

Lexus dealers are over-rated, but I thought they would be the experts since they see this engine day after day. Even if I over paid for the repair, I still have to start over with an independent mechanic, but I get the feeling the O2 sensor might be affecting the knock sensor or maybe another factor is causing the sensor to signal. Just because the sensor puts a code out-it doesn’t always mean it’s bad, so there might be an underlying problem. Just for experimental reasons, I put LUCAS fuel treatment in and filled up with super (92 octane) as I have been doing. Any technical advice out there? All thought appreciated.