hey guys i recently changed o2 sensors in my 2000 mustang gt auto and now i get p0135 mil. i dont understand why though cuz i wasnt on with the old sensor in there but the code comes up with the new one. i unplugged the sensor and cleaned out the connector with electrical connection cleaner and nothing code still there. oh and i do have a predator so i erase the KAM and i clear trouble codes. Also i quick note i read somewhere that the code means that the o2 sensor isn't heating up and will kick up the code, but once the sensor is hot it doesnt matter. so i let the engine run till operating temparature, and cleared codes and kam. went for a drive and 10 miles later code came back on. any help greatly appreciated guys. thnx.

 

I may have posted this for you before, however here are the potential causes for P0135 from the '03 shop manual.

Also, whomever wrote that "...that once the sensor is hot it doesn't matter." didn't know what they were talking about. The PCM constantly monitors and actively controls the O2 sensor heaters on our cars.

You need to check the voltage at the heater wires for sensor 11 (front passenger) and make sure there's 12V there just after starting the engine.

What sensors did you use as replacements? Were they plug-n-play for the EEC-V 4.6L? Our cars need sensors with 3.3 Ohm heaters, many universal narrow band sensors have 6.0 Ohm heaters. You could also check the heater resistance with a multi-meter.