RHW CTS is located between the rear center of the cylinder head (on the water box)and the firewall .It is inaccessible to service with the engine installed due to very limited space.
Most you can check for is a loose connector but if replacement is necessary you will have to get the engine and gearbox out (together) While you at it get the entire engine cylinder head serviced .
Due to the very limited space both engine and gearbox has to be removed together because the ''11'' and 12'' o'clock bolts ,holding the box to the engine cannot be spannered out with eng & Box installed .
Suzuki Manual is no help on this. BTW if you intend to do the engine removal bit , i'd strongly suggest you run the car for a few weeks with the fuel injectors retaining nuts out by at least one turn. With the working conditions you will have the injectors loosen themselves .DYI injector removal tools may not work as well as their manufacturers claim. The only one that works cost about GBP1100.00 .Injectors must be removed before cylinder head and associated components can be serviced.