Do I need MAF sensor??
 

I had a dealer replace the left rear sensor (was throwing PO156 and 161 codes). About a year and few month later, CEL came on and now I have PO161 again(O2 sensor heater circuit malfunction) and pending code PO173 (fuel trim malfunction) stored. And it is the same bank and sensor again. Should I replace it again or is it an indication of something else going wrong?

Check the connector from the o2 sensor to the vehicle. I had the actual socket go bad in mine, where the pins corroded and one fell off, which is what threw the code.

I checked the connection, it appears OK. So do you think that those codes161,173 could indicate bad MAF? I heard that MAF does not have a specific code. I don't want to do a trial and error with O2 and/or MAF, since both are pricey propositions.

I swapped a healthy AMF sensor from my other car to the ML and the CEL is still on and doing its happy routine - 2 days on, 1/2 day off. DCF, did you have the same codes (161, 173) as I have?
I don't really know where to diagnose next...please help:confused: