My son asked me if my def spray could be plugged up, making the regens useless. He ran into this at the bus shop.
Not being able to inject DEF as nothing to do with regen success or lack of.
Plugged def injector could cause high NOx level problems, but the 9th injector would still be able to inject diesel for the regen's to occur and burn soot from the DPF.
The so called '9th injector' injects fuel into the exhaust for regen.
The 'DEF injector' injects DEF for NOx reduction -- whenever it is running.
2018 GMC 2500 L5P CCSB 4x4 Denali - Mineral Metallic; previous '11 LML, '10 LMM and 04.5 LLY