This is how I fixed a KJ 2002 Jeep Liberty Sport 3.7 4wd. If you have fault codes for both pre cat oxygen sensors (heater circuit low) watch this video and save time and money from replacing unnecessary parts and expensive dealership diagnostics. Your problem may not be where i found this one, but I show you how to test and check the entire circuit. Share what you found on yours in the comments below to help others out! If this video was helpful please like share and subscribe!

I know the video is very long, i tried to slow down and explain every step in the process that would take most experienced technicians a few minutes. Diagrams for this Jeep are at the end of the video and I will make a link so you can print them while you work.

P0031 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
P0051 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)
P0135 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
P0155 - 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)