I have a 99 Expedition. The code reads:

Lack of HO251
Switches - Lean
Bank 1 Sensor 1

Does anybody know what this means?

 

It means your Heated O2 sensor on the passenger side, before the catalytic converter, is acting up or is reading a lean condition in the exhaust system on that side of the engine.

 

Thanks for the help.

Should I change the O2 sensor, or is there another reason it's reading the way it is?

 

A lean condition can be the result of a leaking intake manifold gasket on that side of the engine, or it could just be a bad O2 sensor. Without further diagnostics it's just a guessing game as to which solution would solve the problem.

 

Thanks very much for the help.

Is it alright to drive it like this for about a week? Or should I get it fixed immediately? It's running a little rough.

 

Yeah but I would drive it easy and keep the distance to a minimum, like back and forth to work and other necessary trips.