Originally Posted by cycleman2
It doesn't surprise me that the PC III connects something to the 02 Sensor. Once the engine is at operating temp, that is the sensor where the PCM gets its main signal with lesser inputs from the throttle position sensor as to amount of fuel to add.
If you are going to take the 02 Sensors out of the mix then you'll have to provide an artificial voltage reading to the PCM when it is in closed loop mode, which is just about everything up to 3/4 throttle.
Well it surprised the Dynojet people because for years they just recommended disconnecting the O2 sensor on older PCIII USB models to run properly "open loop". Low and behold after getting the wideband PCIII for the GS I was reading up trying to figure out what the harness connection into the OEM O2 socket was doing. I kept seeing the O2 simulators now being recommended for older PCIII to eliminate left over adaptation due to deafault mode for no O2 sensor detected.
To be clear the old O2 sensor is thrown away on the wideband. The new sensor plugs into its own harness that goes directly into the PCIII. There is another branch off the PCIII harness that plugs into the empty OEM O2 socket off the main OEM wiring harness to the motronic. What exactly that does is the question. The O2 simulators I mention above for older non wideband PCIII's also plug into the empty O2 sensor socket in the main harness. It looks mainly like a resistor. It does not plug into the PCIII harness, so maybe something more than just a resistor is going on with the connection to the PCIII wideband on the GS; ie it is being used as an input to the piggyback or to the motronic somehow.