Ok my 1999 Disco II is starting to give me a head ache! I recently replaced the MAF due to a laundry list of codes that where showing. I need rechecked the system and now am showing a P0135 code. I know this is a O2 sensor heater circuit malfunction but my question is this a normal code when a O2 sensor goes out.I would imagine it would pop a couple of codes? My next thought is it might be a broken / loose wire. Is there any way to test the circuit? If so can someone explain how to do such a thing? I have been trying to get this ride inspected for months now and just got a naughty letter from the state telling me I'm headed for a $200 fine and loss of my tag if I don't get this taken care of.

 

I am not sure if the code is normal, but the heater going bad is a common malfuction.
You might just want to replace both of them and be done with it.

 

How many miles on your truck?