Code P20b9 and “service exhaust system” warning on

Hi:

I believe that code is related to the DEF system running it's own self test and not the heater. Try this. An onboard test must be commanded using a scan tool. A fluid quality test or a forced REGEN will make the monitor run and the messages should clear and the system should return to normal. Basically, you need to force a fluid quality test using a scan tool.

Try this and let me know if it helps.

Joe