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thanks bro yeah..coolant is nasty shit in the wrong place

For anyone else chasing this nasty 1688 code down and attempting to clear the code, also look for a weep of oil that may have run down the wiring harness into pins within the plug. Thus short-circuiting the initial MOP self check.
If you find this to be the case then use a decent amount of degreaser spray on entire plug (both sides of each connector) then same with electrical contact cleaner.
My high km engine has a slight oil leak from an unknown location nearby MOP, hence the 1688 and CEL. I did all of this 3 months ago only to arrive at this point (I just thought it was dirty connectors or the switch that needed adjusting at the time!)
This time round I used electrical tape to keep the slow oil weep out of the connector and therefore not trigger the 1688 and limpy that comes for free with it! Hope this helps someone else as I have spent countless hours researching this PIA debilitating issue.

I really hope this gets me through to rebuild time without related issues, fingers crossed!

Thank you for sharing that advice! If someone is searching and finds that info, it may save them a bunch of time diagnosing the issue.