My pressure gauge has not been running in what used to be its normal range. Any suggestions on the best way to check if this is the problem? Also, any suggestions on a replacement part? Is this like the O2 sensor that needs to be a Toyota part or can I simply grab one from autozone? As an FYI, I recently had the engine rebuilt and the oil pump was replaced at that time, and the pressure gauge was registering the same after the rebuild for the last 4 months. It was just in the last week that while driving I saw it go up to H for the first time and now while idling after the engine is warm, it will hover on L.