Code 51
WARNING: This page is about a different car, the 1995 Jeep Wrangler, 1995 Jeep Grand Cherokee, and 1995 Jeep Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
Scan tool displays O2S STAYS BELOW CENTER (LEAN). Condition is: oxygen sensor input indicates lean air/fuel ratio during engine operation. MIL will come on.