Hi xgrapher,
From your first post I think you want to scale the output as a function of something an arduino calculates.
So for instance if your scale factor goal is 0.9 then a normal 5V out would be 4.5V and a 3V output would be 2.7 V. Am I understanding you correctly?
I've worked with this sensor some years ago in a fuel tank leak system and recall the output was proportional to input voltage. So I see two options:
- If you don't require a large range of scale factor you could simply modify the input voltage (Vcc). This may not meet your "don't cut a wire" goal.
- Load the sensor output with resistors. Some DAC's can be wired this way but I don't know if they can handle the current needed (which is unknown at this point). Alternatively you could 4 Mosfets, each grounding a resistor tied to the sensor output. This would give you 16 combinations. I believe it will not damage the sensor as all automotive sensors must be capable of extended short circuits on their outputs. Caveat, the sensor output impedance may not be constant for all conditions (especially temperature)
Good Luck.