Posted by Keith in Washington [172.71.151.122] on Tuesday, July 01, 2025 at 16:15:36 :
In Reply to: Re: OT: NOX sensor and module posted by jay massy [172.71.150.215] on Tuesday, July 01, 2025 at 15:14:52 :
Sensor 1 and sensor 2 are different. They physically look the same but are always listed front and rear with different part numbers. The front heater apparently heats to 600 degrees whale the rear apparently heats to 1200 degrees. Theses are wideband sensors with 8 wires of which 6 go to the sensor. The other 2 seem to go to a resistor. The PCM controls the voltage through the heater grounds as they are directly wired to the fuse box. The PCM allows full voltage at start up and decrease it as it detects the heater temperature increasing. As I understand the front sensor acts as an O2 sensor while the rear is a NOX sensor which is the reason for the temperature differences. You can run for a while without the rear sensor as it is monitoring the catalytic converter (apparently the 11 and 12 model years did not have the rear sensor). The front sensor is used to determine lean/rich fuel conditions and must be operational. I can actually watch the front sensor, at start up, be non functional then as the sensor hits operational temperature I can watch the O2 levels with my code reader/dianostic tool.
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