Both forward O2 sensors need to be replaced at the same time anyway, just replace both forward sensors and don't worry about which is which. You don't replace just the sparkplug that's misfiring, do you? Well, maybe you do, but it's the kind of thing that leaves you constantly working on your car. If one's gone bad the other is close behind.
99 Durango doesn't have a Heater Control Valve, It only has a thermostat
If it is saying that the heater circuit has failed then this O2 sensor has failed. The o2 sensors have tip heaters in them. These are irreplaceable. Replace the whole sensor. This particular sensor is located on the driver's side exhaust in front of the Catalytic Convertor.
It should be located on the passenger side floorboard well, just below the glove box area
Trouble code P0042 means: HO2S Heater Control Circuit (Bank 1, Sensor 3)
H02S Bank 1 Sensor 3 Heater circuit. This should be the H02S (heated oxygen sensor) located after the catalytic converter. If the wiring looks okay the sensor is probably bad.
Bank 1 is the bank of the engine that contains #1 cylinder. Bank 2 is the other bank. Sensor 1 is located before the catalytic converter. Sensor 2 is located after the cat converter.
A Dodge Durango does not have a water control valve in the heater plumbing. The cabin temperature is controlled with airflow control doors.
On the bottom of the heater/ac assembly in front of the passenger compartment . YOU KNOW BEHIND THE DASH .
The heater control valve is located under the hood on top of the passenger inner fender near the firewall. It has a wiring harness going to the rear of the valve and has also two coolant hoses attached.
Its a Durango.......not a Drango.
How to replace the inside Spectra Heater Core on a 2000 dodge durango??
You may want to check your model year. There is no such thing as a 1990 Durango.