High Coolant Temp warning after EGR cleaning

Make sure it is the correct way. You should not have to FORCE it....
Using plyers you could crack the connector.

It usually is a tight fit just as it snaps into place. So make sure the pins align and
that the "lock" is in the correct place.

 

Did it make a nice click? Are you able to pull it back off without squeezing the release tab?

If it clicked and you can't pull it back off without squeezing, it's ok.

If you can't get it to click, and you can pull it right back off, then something is in the way. You should not need a lot of force to plug it in.

You could pull it back off and examine carefully for anything in the way. Maybe use a mirror on a stick to look in the connector on the sensor itself to see if either pin is bent, or some piece of junk is in there.

You can look in the wire harness, for a glimpse of the rubber gasket (usually red in color, I think) that goes around the outside, looking for any place it might be sticking up or kinked,

Sometimes after years that rubber gets a bit hard, and won't slide over the sensor connector as easily. I've found that a very tiny dab of a silicone grease, on the outside of the sensor connector, right around the edge that will have to pass through the gasket, can work wonders. (There is a Ford Motorcraft silicone grease, XG-3, that is amusingly sold for disc brake caliper lubrication and electrical connectors.)

Edit: also, if I remember right, that little wire harness is only several inches long, a little extension from another connector closer to the cylinder head. If it really doesn't want to plug in, you could try replacing that little wire extension.

 

Mine looks about the same; I’ve never touched it.

 

There’s no locking lever on the back? It’s so far back I could barely touch it, but could feel something on the far side.

 

it doesn't have to go all the way over. Just far enough to click.

Is it possible your SIL broke off the clicky bit while removing it? Then it's just a matter of pushing it on and thinking secure thoughts.

This looks to me like a possible busted place;



That little wire extension, if my research skills haven't failed me, is part number 82124-47040, and probably under $20 brand new in a box from a Toyota dealer that sells at discount (list is about $26).

This picture shows the little extension with the actual sensor plugged in at the end, but of course the 82124-47040 part is just the wire extension.



Pulling it off a salvage car should be even cheaper. Just don't break the clicky bits pulling it off!

... that happened to me once. There was a particular clip that I needed for an old car I was driving, because the original one had broken. I went to a dealer, and the guy said "that's no longer available. But wait, I think we have an old parts car in that model around back", and I walked around back with him, and sure enough, there was the car, with the exact clip I needed. He wiggled it for a bit, then said "just a sec", and before I could say "oh, no problem, may I try?" he came back with a big screwdriver, broke the clip off, and handed it to me.

 

You could wrap a cable tie through the open part of the connector and around the lower
part of the sensor....

 

We've already learned a new thing, that the red thermometer light doesn't only come on for HOT, it also comes on for unplugged (which, with an NTC thermistor, reads as REALLY COLD).

For that sensor, anyway. Haven't tried with the one in the cylinder head.

 

Glad all is well. Check the coolant tank to make sure you have enough coolant.
And you can use a smaller cable tie.
The duct tape might fall apart from the heat..... Check it once a week or so and see
how it's holding up...