My 2005 Trailblazer had been running rough for a few months. It was so rough that the motor actually stalled on two different occasions when stopping for traffic lights. I tried fuel injector cleaner with no luck. One day the check engine light came on. The code said the cam timing sensor was at fault. Within an hour of installing the new sensor the fault came back. Another new sensor was installed with the same result. After a phone call to GM the oil was changed. It had been about 5,000 miles and 8 months since the last oil change and the oil change light had not come on, but the oil was dirty. The folks at GM said sometimes dirty oil will stop a new sensor from getting a good reading. Changing the oil solved the problem. The new sensor also stopped the rough running I had been experiencing for the past few months. Drives like new now. I did find a YouTube video on replacing the cam timing sensor. The video said the motor will run rough and even stall if the sensor is not working properly.