Big 300 having some minor surgery. Check engine light came back after a long time of not seeing it. A couple of my less than great repairs came to haunt me. Apparently running the O2 heaters for 10 minutes solid is just tooooo much and they have failed altogether. I’m not surprised. Instead of eBay I bought 4 new ones from Rock Auto made by NTK which is the OEM manufacturer. The internet says they are superior in that they heat up faster, so I will rejigger my timer to 60 seconds instead and see if that does the job of pre heating them so it goes into closed loop again. The knock sensors also threw some codes saying wiring fault and sure enough the broken connectors were loose. You can buy new knock sensors with a new plug so I assume this is a common issue. Didn’t quite finish the O2 sensors so this will have to continue on Saturday.