I’m replacing my starter in my 97 Disco and this has broken. I’m sure the plastic is brittle and the metal bits are broken as well. Any idea what this is and how to replace it? It has a blue housing.

 

After looking online I’m thinking knock sensor?

 

Yes, it is the knock sensor. Sensor is probably broken and the connector is fine.
Should be able to grab a new one from bearmach or another company.
I want to say its part# ERR5594

 

Yep, broke Knock Sensor.

 

What the heck is a knock sensor?

 

Senses pre-ignition, engine ping. Retards timing that happens with low octane gas, for example.

 

No doubt it is the knock sensor. You have another one on the other side of the car.
I barely bumped mine over the Summer 2020 and it broke as if it was a 20yr piece.

NOTE:
When you get a replacement be sure to hand tighten it first. I had the awful experience of getting a sensor with a damaged thread (did not know it at the time) so this made it a PITA to screw it in, let alone torch it down so you can plug in the connector.

The first few threads of my sensor was jacked so after hours and hours I ended taking a dremel smoothing out the bad threads.

I always give myself 3X the amount of time to do home and car related projects.
Hope this helps someone along the way.