Purchased a 2000 ES 300 for my mother in law. When driving the car home the check engine light came on. I stopped at an Advanced Auto where they read the code and said it was an o2 sensor. No big deal I can replace it. I changed the water pump, timing belt, serpentine, and brakes. During the process I also put in a new battery and engine light disappeared. I had the car for about 5 weeks after all the work but before delivery (she lives in another state). I drove it around town with no return of engine light and car drove wonderfully.

Last week I drove it to her and after about 45 minutes of highway driving the check engine light came on. I assumed it was the o2 sensor. I continued my 3 1/2 hour drive at 70 miles per hour with the car performing great! No loss of power, great miles per gallon. Upon my arrival I told her she would need to get one of the o2 sensor replaced as a light had come on during the drive and I had previously determined the problem.

She called me last night after taking it to the local Toyota dealer who wants $800 to replace a knock sensor. After some online research I believe that if a knock sensor is bad the car should be running rough and get bad gas mileage. Anyone have experience with this?

Thanks.

 

A knock sensor code will not make the engine run rough. The Ecm will retard the timming, which will reduce power. The reduced timming will also reduce gas mileage, but you might not notice the amount of the reduction.

 

Thanks for the reply. Any idea why it only comes on when driven on the highway?