Cel only on after 5 miles over 55 1996 4.0 manual

[lowrange50]

Hey guys and gals new here. I have a 96 4.0 manual that the CEL only comes on when driving on highway over 55 mph after around 5 miles. CEL will stay on if started and driven for a couple days after. If I let it sit 3-4 days CEL will be gone. Checked code and was front O2 sensors. If I drive it around town the CEL never shows up. Ideas? Thanks for any ideas!

 

[bimmerteck]

Could be a small vacuum leak making the front o2 sensors look sluggish, or the actual front o2 sensors wearing out. The monitoring for o2 operation only happens when the ACU detects certain parameters are applicable which is why it may not even test them until it warms up. What the codes says about the o2 as well as any freeze frame data captured upon it's setting would be helpful for diagnosis.

 

[lowrange50]

I will try to replicate this in the next couple of weeks and get back with results. Thanks for the reply!