wfortado

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?

Bustedback

http://www.obd-codes.com/p0155

May not be the sensor, it could be an open in the wiring to the sensor.

BuckB91XJ

I had this same exact problem with a 2001 Ford Expedition I had. What it ended up being after the stealership soaked me for 3 O2 sensors was the wiring to the O2 sensor was rubbing on the exhaust manifold. It ended up chafing through the insulation and then the bare wire was chafing against the manifold with vibration causing it to the throw the code and CEL. I'd take a look at your wiring going to the O2 sensor. I bet you find your problem.