This truck will have a Weather-Pak four-pin connector, most likely four in a row located somewhere on the harness with just a cover on the end to protect the sockets. Short pins A to D to access blink code functions. As mentioned you will need the code list, and you will also need a qualified technician to interpret those codes correctly. An O2 sensor code does not automatically mean you order and install a new O2 sensor and bingo problem solved, you need a knowledgeable mechanic to determine why that code was tripped in the first place. A properly working O2 sensor can detect an abnormal level of oxygen in the exhaust and throw a code, and a brand new replacement sensor will do the same thing unless the cause of that abnormal level of oxygen is corrected. If you do not have the skill required to interpret those codes properly, you may end up spending far more money throwing parts at the truck than you will spend in labour to have a certified tech perform a diagnostic service for you.

We had the same problem finding the plug, We found it Under the floor plate on the leftside when you are sitting on the unit. You just need a paper clip or a jumper wire to get the codes to read out at the dash. you will need the list of codes

Good Luck

It's not a car. it probably doesn't have an OBD2 connection, and uses a computer hookup related to the propane manufacturers emissions system.