Mercruiser Fault Codes
 

We bought a 2012 Sea Ray Sundeck 240 with a Mercruiser 350, 5.7 Bravo. Since we bought it we are getting a code 48 stbd exhaust oxygen sensor not working properly. We had our mechanic replace the precat sensor and reset the code. 2 hours later we got the same code so he replaced the post cat sensor. Not even an hour into that we got another code 48 and now are getting a code 50 as well. Can anyone offer any advice on the problem here. We just bought this boat and are extremely frustrated. Thanks