Under normal conditions, the pcm uses the O2 sensor to monitor the exhaust to ensure the the air/fuel mixture is burning completely and cleanly. Called "closed loop" operation, this is done to minimize emissions, maximize fuel economy, and make sure the catalytic converter doesn't get over heated or fouled by excessive, unburned fuel. The pcm watches the readings from the O2 sensor and adjusted the fuel trim (injector pulse) to keep the air/fuel ratio near stoicheometric (14.7/1) for the cleanest, most efficent burn possible. When accelerating, however, more fuel is needed for the requested extra power...at that time the pcm goes into "open loop" and ignores the O2 sensor in the interest of more power.


the reason that you notice this more on longer trips is that the code is indicating a long term fuel trim issue. what that means is the pcm will try to correct for a overly rich or lean condition by adjusting the short term fuel trim (tune). if the short term trim is consistantly rich or lean, the pcm adjusts the long term trim to compensate. however, once the long term gets beyond a set point (usually 18-20%) the pcm gives up trying and will set the dtc. short trips don't last long enough for the long term trim to get "adjusted" to the fail point.

this dtc can be caused by a skewed O2 sensor reading which feeds the pcm a false rich or lean reading
It can also be caused by a real lean or rich condition - incorectlly sized injectors or wrong fuel pressure

if you are getting this dtc, then it is very unlikely the the O2 sensor is disabled in your tune.


easiest thing to adjust is the fuel pressure (adjustable regulator) ... 3-4 psi lower (or higher) may be enough to keep from dtc trigger point.