Sensor 1 is the upstream sensor. It's the first one back from the engine. On general principle, I'd change both upstreams, if one has failed the other may not be far behind. Yes, disconnect the battery when you are working on it.

 

There is no code with such a description.

1. Identify your truck fully. We are not psychic.

2. Get the exact fault code(s). Pxxxx where xxxx is a four-digit code.

3. See if the code(s) have been previously discussed or diagnosed by plugging them into the SEARCH tool. You'll find that many of the common ones are just that, common and well discussed.

4. Diagnostic Test Codes (DTCs) are NOT instructions to replace a part, they are diagnostic data points that are used as part of a logical troubleshooting sequence designed to find and fix the problem the first time.

Steve