Check engine light indicating oxygen sensor failure. Since I had brought the car in to the same Ford dealer service dept for the same problem 5 times before, the service manager was familiar with my car. He indicated that the trouble ticket they had submitted didn't result in any new solutions from Ford. He did say that they would check the car thoroughly for a possible cause, and might have to check the wiring and possible re-do some of it. I was expecting that this would take a few days but they called me a few hours later and told me the car was ready to go. Service notes indicated the tech had tested the circuits and found them to be fine, but found the sensor component resistance high, so he.... replaced the oxygen sensor again and stated the car now works as designed.

Apparently the Ford Focus is designed to have the 02 sensors replaced more often than the oil is changed.

Of course, the check engine ight came back on again after about 500 miles, but I have not taken the car back there since I can only expect the same result. I work from home so put little mileage on the car; it now has 30,000 miles on it and it has gone through 6 O2 sensors. Extended warranty will expire soon and I plan to file claim. Just need to find a lawyer with NH lemon law/Magnusson Moss expertise.

Oxygen sensor failure, this time at approximately 27000 miles.. Ford Service Manager said they were putting in a new trouble ticket with Ford. Technician replaced oxygen sensor but could not find any other solution. This was 5th failed oxygen sensor so I was ready to talk about making a lemon law claim but service manager stated that if it happened again they may have a permanent fix as a result of the trouble ticket, and if not they would do a thorough examination of the car until they could find a solution.