Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

2001 Lexus ES 300 check engine light - knock sensor codes

On highway driving only, if I come to a full stop at a light, AFTER gradual acceleration, I see that the rpms move to between 3000-4000 rpms (normal rpm speed is 2000 when driving at speeds of 55-65 mph). What are possible causes? FYI I’ve checked the codes for the check engine light which points to fault in Knock Sensor 2 electrical circuit bank 2 and Knock Sensor 1 circuit bank 1 which was replaced recently. My car mechanic who has serviced my car for years believes the CEL is a computer blip and finds no problem with my car. But the symptom I describe still remains. What areas should I look at to solve this? Are these expensive to fix? I’m not savvy re: cars so please let me know what I should have a mechanic check out. I’d appreciate a response soon, if possible (this is my 1st time posting a question online so maybe this is unrealistic.)

Tell any mechanic, yours or another, exactly what you’ve posted here. If you try and tell the mechanic what to check or what to fix, they will and the problem may not be found and you will out some cash. Let the professional diagnose the problem and expect to pay them for their diagnostic time.

That said, it is unlikely the knock sensor will have anything to do with the rpm rise. That may be a transmission problem or it may be normal for your car - you don’t say if it has just started doing this.

If your current mechanic is telling you to ignore a check engine light that is setting an actual error code, find a better mechanic, this one isn’t very good.

Thanks, Mustangman, for replying quickly and giving me helpful information, both with mechanics and about possible causes of my problem. This symptom has been going on for months. I’m seriously considering trading it in since my “research” and your comment makes me think this will likely be an expensive repair.

It does seem like a transmission problem. An owner’s manual might list conditions that cause a CEL to come on and it might even say drive train or transmission problem. Some of those problems are not expensive to fix

Knock sensor codes can be triggered by rattling noises or loose valve lash. So you may not be getting any useful codes because the engine noise increases with engine speed. So if you solve the problem of high engine speed you might solve the knock sensor code problem too.

Thanks pleasedodgevan2 for your suggestions. I checked the symptoms with Lexus service and, you’re right, he believes everything points to a transmission problem that he estimates will cost at least $4000. So, I think it’s time to trade in my 18-year old car for the next one.