Hi I'm over in the England with a 93 ETC. Just found your site for the first time and I'm fascinated in particular with a recent entry on codes. This has helped with my understanding of code 52 PCM Keep Alive Memory Reset (dead battery). I also have history code 42 (left front oxygen sensor lean) and current code 44 (right rear oxygen sensor lean). Does anyone know if I change this sensor will the code go away and stay away once I've cleared the codes or is there likely to be another problem that the sensor is picking up.The code alternates between history and current as I drive the car so that the Engine Service Soon light is on when it shows current and off when it shows history. Thanks Rod Bevan

Sounds like the sensors are working fine and detecting a lean condition. I'd look for a vacuum leak.

Thanks I'll try looking at that. Are there any likely areas for leak please? I have the Chilton and Haynes Manuals. I've had quick look around, the pipes seem ok, so I cleared the codes and went for drive. After a short time the engine service light came on and code 44 current now shows. Other codes that show are AO46 history and SO55 history. Fuel consumption seems poor as well. At 7 dollars for your gallon it was bad enough before, but it's normally a pleasure to drive Rod Bevan

On a '93/'94 look (listen) around the intake manifold cover. If all is well ,there, start checking all the vacuum lines.