P1621 code after misfire repair?

[LOBBS]

Has anyone ever dealt with a p1621 code? I got a few misfire and lean codes on my 2018 Rubicon with the 3.6L. Put in new spark plugs, coil packs and changed out all 4 O2 sensors. Those codes have gone away and the Jeep is running great. I had expected the permanent codes to clear over the last week but the CEL stayed on so I had codes pulled again last night and this new one has popped up for a low reference voltage. A quick Google search says to check the fuses for the PCM and all of them labeled as such under the fuse panel (F22, F23 and F80 IIRC) all look good. The search also says to check the fuse for the O2 sensor heaters but I'm not seeing a label on the diagram which would point to that fuse. Just trying to nail down as many options that it could be before breaking more clips pulling the front fenders back off to get access to the O2 sensors again.

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[RhinoJLU]

Did you ever figure this out I’ve had that same P1621 code for months now all I’ve done is check the grounds and checked the O2 sensor wires for damage