99 Yukon 5.7 intermittent starting issue after using block heater

[1990Z71Swede]

Flat-blade to flat-blade should be "about" 35 ohms.

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Either flat blade (doesn't matter which one) to the round "ground" pin = no continuity. Continuity indicates problems which could be as simple as snow or water making a conductive path when the extension cord gets dropped on the ground.

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I would start out by testing at the extension cord, where it plugs into the receptacle in the garage. The first test may read a bit higher in the ohms value due to the length of cable in the extension cord.

If you have no continuity from flat blade to ground pin at the extension cord, I don't know why your GFIC tripped unless it was stray moisture somewhere between "hot" and "ground". If you do have continuity, test again at the block heater cord to eliminate a fault in the extension cord.



I'm not aware of any connection between a faulty block heater and failure of various sensors. Doesn't mean it couldn't happen, just that I don't see a cause-effect relationship from here.

I'm thinking that this CPS failure and block-heater use was coincidence; or perhaps both were due to the "deep freeze" mentioned.

One thing about using a DMM for finding isolation issues in 110/230V equipment.

A lot of times a DMM is all a guy has

But the same guy need to be aware that some isolation issues does not show with the low voltage probing a DMM is capable of, typically issues caused by humidity and or corrosion may not be detected.

I have had this exact issue with a block heater, measured fine with a DMM but plugged into 230V... Fireworks, and blown fuses. Turned out to be a small crack in the plastic connector housing leading to water ingress and corrosion of the ferrous connectors which eventually was severe enough to cause arcing.