Had my check engine light on. Put a code reader on it to see what it was. It went off on its own a few days later. Went to dealership and told them what the code reader said it was before it went off (P015B). The code has to do with the PCM and an O2 sensor communication. My truck still has emission warranty. Service person told me the problem can't be solved since the light isn't on anymore, even if the code is still in the history. Is this true? Or are they just being cheap and lazy not wanting to do warranty work? Thanks.
Yes, it is an accurate statement. The first troubleshooting step I do when diagnosing any issue which is in response to trouble codes is to clear the code and see if it comes back. If it doesn't come back, the issue was a "fleeting" issue, meaning to me as not something to really worry about.
Along those lines, considering your truck is relatively new, the code P015b is just saying the O2 sensor was lazy for a minute (or two) and the computer recognized this. This isn't a code I personally would worry about too much, but this doesn't mean I'd completely disregard it. Once cleared and it doesn't come back, it should be fine. If you haven't done the proper maintenance with the O2 sensors, you should consider doing this. Remember, they should be replaced every 100k miles along with the plugs and wires. There's some other stuff you'd want to do as well, but consult your Owner's Manual for those details.