ST170 have a reputatation for eating lambda sensors. Both your codes relate to Bank 1, which isn't surprising as it isn't a multi bank (ie V) engine.

The heaters are switched directly by the PCM IIRC, no relay, and are only turned on for a faster warm-up. Once a good signal is being received they are turned off. So the fault does not affect the normal fuel/air control at all.

As you intend, check the wiring and resistance of the heaters (the 2 white wires at the sensor). Also use a switch cleaner on the connectors. Although sealed the contacts do still oxidise.

Martin