here's 2 screenshots from Autodata, pretty straightforward task just made a little fiddly by the location of the plug (on top of the gearbox near the thermostat housing)

usually the cause of over-fuelling and rough running, doing these few checks are likely to be a rather more accurate way to diagnose a fault rather than just unplugging it.

as well as the checks below its worth checking the loom back from pins 3 and 4 to the ecu Pins 4 and 22.

ECU Pin 4 is the ECU earth Circuit, and at idle Pin 22 should have a 0-1V fluctuating input signal.

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need a part number? get on here - http://public.servicebox.peugeot.com

Bring on the Trumpets.

Just tried this for you, mine reads 4.4 ohm. And my sensor is working like it should.