On 2WD CTS is on inlet side at the rear of the head, behind inlet manifold, not sure on 4x4, it is a thermistor and it won't do any harm to replace it if you do suspect it's this, (They are cheap enough) being a thermistor the output can give false readings after a while. The ACT is exactly the same sensor in a different housing.

The ECU uses a flash code system for fault diagnostics, it will only log an error if a sensor goes totally open or closed circuit IIRC, once you turn the ignition off any faults that have been logged will be lost! Trouble is some remapped software does not keep this facility!

Martin