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Heated or Unheated O2 sensor?

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I've got an 89 comanche with only 1 Oxygen sensor on the manifold. It is 3 wire, however when I went to napa to get a replacement they had two options listed for my truck. Bosch BSH 12008 (heated) and Bosch BSH 12009 (unheated). What made me question which to purchase is they recommended Unheated, but it's on the manifold/header so I'd think heated. I looked in the FSM for the 1990 that I found online and I only see heated.


So I checked with autozone and they too recommend the unheated O2 sensor for the truck. Can anyone advise me or explain the difference between the two?


Truck is 89 4x4 I6

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And what really makes it more confusing... Napa states the NGK 23553 (heated ) is comparable to the Bosch 12009 (unheated)



I guess what my question is am I better off ordering the one that states heated like the NGK... Problem is the only ones that are at parts stores instock in my area are the Bosch 12009 and some other brand that is also designated as Unheated.


Will the truck run the same or will the sensor just not last as long etc...

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Answering some of my own questions, but still wonder why the bosch that is recommended in unheated and our fsm shows heated. Turns out heated vs. unheated does not matter on location, but means it has an internal heater.


Heated oxygen sensors have an internal heater circuit that brings the sensor up to operating temperature more quickly than an unheated sensor. An oxygen sensor must be hot (about 600 to 650 degrees F) before it will generate a voltage signal. The hot exhaust from the engine will provide enough heat to bring an O2 sensor up to operating temperature, but it make take several minutes depending on ambient temperature, engine load and speed. During this time, the fuel feedback control system remains in "open loop" and does not use the O2 sensor signal to adjust the fuel mixture. This typically results in a rich fuel mixture, wasted fuel and higher emissions.


By adding an internal heater circuit to the oxygen sensor, voltage can be routed through the heater as soon as the engine starts to warm up the sensor. The heater element is a resistor that glows red hot when current passes through it. The heater will bring the sensor up to operating temperature within 20 to 60 seconds depending on the sensor, and also keep the oxygen sensor hot even when the engine is idling for a long period of time.

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As it turns out the Bosch BSH 12009 is heated, there was an input error awhile back by bosch in their product descriptions... They have since corrected it, but most of the retail parts stores have not updated their catalog info from the vendor.


the BSH 12008 is for the 2.5 motor not the 4.0 a glitch that was in the napa system.

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