Mercedes-Benz Y129 AdBlue DEF Metering Valve Teach In – Reset – Program with YOUCANIC Scanner

About this video

In this video we show how to teach-in / adapt the Y129 AdBlue (DEF) metering valve/injector on a Mercedes-Benz using the YOUCANIC UCAN-II scanner. This is the calibration/reset you perform after replacing the DEF injector (metering valve) or completing SCR/AdBlue repairs, so dosing matches the new hardware.

Note: Teach-in/adaptation does not fix a faulty injector, wiring, clogged lines, low-quality DEF, or a failing SCR catalyst. Diagnose and repair root causes first.

What you’ll see

Connecting the YOUCANIC scanner & identifying the vehicle

Navigating to SCR/AdBlue module → Metering Valve (Y129) Teach-In / Adaptation

Running the teach-in and confirming completion

Optional: dosing quantity test & live data checks (NOx, temps, dosing status)

Clearing faults and verifying readiness/road test tips

Common symptoms of a bad Y129 injector (metering valve)

“Check AdBlue/DEF” warnings or Start not possible in XXX miles countdown

Check Engine Light with SCR/NOx/AdBlue faults

Ammonia/chemical odor, white DEF crystals around injector or tailpipe area

Reduced power / limp mode due to SCR derate

Poor SCR efficiency or repeated NOx exceedance after sensor/catalyst repairs

Frequent regens or failed emissions readiness for SCR/NOx monitors

Related DTCs you may see (examples; vary by model/year)

P2047–P2051: Reductant injector circuit/open/short

P20EE: SCR NOx catalyst efficiency below threshold

P204F: Reductant system performance

P207F: Reductant (DEF) quality/performance