I got the P0155 code on my 2000 Grand Cherokee with the 4.0. It said to replace the o2 sensor. I replaced the sensor, and the light did not go out. I read online that it might take a few days, or driving it about 100 miles, so we did. It still did not go out. I rescanned it, and it was the only code, so I cleared it. It came back on about 2 days later, so I checked the fuses, they were fine, so I rescanned again, and it was again the same code. Cleared it again, and the light came on about a day later.

Any ideas?

 

Try reposting in the Grand Cherokee section