Why do tire pressure monitor show "0" for the LF tire?

Question: I have a 2005 Yukon Denali and the "check tire pressure" continues to show. We manually checked pressure and all tires are 33 to 34 lbs. The monitor shows "0" for left front tire and we can not get it to reset. Already Tried: Reading manual and re-setting monitor with buttons on steering wheel. Answer: This is an indication of a failed sensor in the wheel. Have it replaced. Should run you about $110.00