Mercruiser 4.5 Fault Code
 

Hello,

New to the forum! I have a 2017 Searay SPX 210 with the Mercruiser 4.5 (200HP). It has been a horrible boating season thus far. Early June, service light came on. Took out of the water later that month and dealer said 1 of the trim senders assemblies went bad (3 wire/1 puck version). Got it back from the dealer, launched it, and not even 5 minutes later, light was back on.

This time, I decided to purchase the Mercury Vessel View Mobile, instead of the $100 per time computer scan from the dealer. Code is reading as follows:

851-11: O2 sensor Port S2

Does anyone know if this is the pre or post CAT sensor or should I just do trial and error and replace one to see if it corrects? Is it possible it's not even one of these sensors at all?

851 is post cat and the 11 means lean condition. No offense but not that much info to be had for production catalyst marine engines on the forums. I work on these and been thru many training programs from the OEMs.

Thank you for the info! I ordered the part and will swap it out when it comes. Hopefully this is it and not something deeper in-bedded.

the easiest test to do is swap post O2 sensors and see if the code shows - 871 - 11 - then that would tell its the O2.

871 is post cat starboard O2

the easiest test to do is swap post O2 sensors and see if the code shows - 871 - 11 - then that would tell its the O2 issue itself.

871 is post cat starboard O2

So silly question, but are the post/pre O2 sensors different or are they the same part number?

doesn't that fall under the emissions warranty?

engine serial number tells it all. Early cat versions were Narrow Band O2 s and then they went to wide band and narrow band O 2 s

warranty depends on years of ownership and hours for emission controlled engines - warranty is 480 hours its over with EC engines