P0135 SUZUKI - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1: Engne light

The engine light popping appearing on my 04 Jimny has brought up the fault code P0135 02 HT CM MAIF which, through a web search , suggest the problem as in the thread title.
The initial response from the garage who found this was that it could be worth checking for a dodgy connection or joint first. Now then, where on earth do I begin to look?
Any other bright ideas apart from, at this stage, taking it back to the garage?

Are these things testable? The web gives me a variety of prices and I am assuming that a genuine part will be fine but a pattern may or may not be exactly correct and thus not solve the problem. No point in doing it if the light stays on as its for sale. Can't work out where the exact fuse is at the moment .

The heater can be tested using a DMM on ohms. A pattern O2 sensor will be OK but its worth spending a little extra to get one with the correct connector so you don't have to hack the wiring about.

I got this error after doing my Liana engine swap. The Liana sensor i had left over from the swap was the wrong connector, but an older Baleno was a straight fit but with a longer wire. Remember to lube the threads of the sensor as these easily seizes. Had to fresh up the threads with some filing to get it back in.
The connector sits fairly close to the manifold with the short wire and has a sloppy heat sheild on the wire, so it sure is a thing to check for good connection.