Intermittently Heavy Steering After Replacing Power Steering Yaw Angle Sensor And Battery

[Swoxy]

My car has intermittently heavy steering. I replaced the power steering yaw angle sensor in September 2008 which cured the steering problems until now. I replaced the battery in July 2009. What could be causing the problem?

[cjb]

First scan the car for faults, if that returns nothing, check/clean the battery connections, earth straps, and connections to the PAS pump.