98 mazda b4000-p0153

Hello, I just bought this truck.2nd day it comes up with this code.I've been reading other posts on this subject and twopossible causes are vacuum leak and exhaust leak. They put a new muffler on for safty check so the exhaust has been worked on. Also the temp.switch to change from hot to cold doesn't work, this is a vacuum operated valve, this also could sujest a vacuum leak. any help on the error code or the heat switch would be great. Thanks

If the shop or dealer just sold it to you and they just put a muffler on it then take it back to them. it might be an unplugged 02, why pay for repairs on something that they just sold to you?

Ya your right,but I had the reader so I was curious. I checked the wireing to the o2 sensor like they said ,it looks fine, no aparent exhaust leaks any where. I thought the Possible vac. leak was ineresting sine the vacuum operated heat valve isn't working.If I turn the selector switch off ,the valve closes(goes cold)but the temp.switch won't operate the valve.