Just come back from a couple of weeks on holiday in France. A few times on the journey the CEL has come on and stayed on usually only going out either by stopping and restarting or lifting completely of the accelerator for several seconds then it goes out when the trottle is opened again. Only happens on long motorway runs not around town. Diagnostics show an O2 sensor fault. Obvious first step is to change the sensor, but is there likely to be an underlying fault?

Graham

 

Sounds like it is the lambda - especially if the CEL is coming on while travelling up hill on light throttle. Change of sensor should fix it.

 

Lambda (O2 sensor) faults quite common on all cars these days. You will probably be running rich and consumption will be down. If you have wrx with all the cats change it sooner rather than later as the unburnt fuel from rich mixture can damage the cats.