Engine | 608 in model 118, 177, 247 |
with code U79 (BLUETEC (SCR) diesel exhaust treatment, generation 3) | |
Engine | 654 in model 118, 167, 177, 247 |
with code U79 (BLUETEC (SCR) diesel exhaust treatment, generation 3) | |
Engine | 654 in model 213, 238, 257 |
as of model year 2021 | |
with code U79 (BLUETEC (SCR) diesel exhaust treatment, generation 3) | |
Engine | 656 in model 167, 223 |
with code U79 (BLUETEC (SCR) diesel exhaust treatment, generation 3) | |
Engine | 656 in model 213, 238, 257 |
as of model year 2021 | |
with code U79 (BLUETEC (SCR) diesel exhaust treatment, generation 3) |
P49.20-A050-79
Example illustration of metering valve |
1 | Exhaust gas aftertreatment metering valve |
Overview
This document contains information on:
General
Function
General
The exhaust gas aftertreatment metering valve is used to inject the AdBlue® reduction agent into the oxidation catalytic converter. The exhaust gas aftertreatment metering valve also has the task of aerating and ventilating the pressure line.
Function
The function sequence is described in the following steps:
Fuel injection
Ventilation and deventilation of the pressure line
Fuel injection
To reduce the nitrogen oxide content, the exhaust gas aftertreatment metering valve sprays the AdBlue® reduction agent into the exhaust system upstream of the SCR catalytic converter; the SCR catalytic converter then converts the nitrogen oxides into water and nitrogen.
The exhaust gas aftertreatment control unit transmits the quantity of reduction agent injected to the combustion engine control unit. The control unit takes this into account in the subsequent computation of the necessary quantity of reduction agent.
Ventilation and deventilation of the pressure line
To aerate and ventilate the system, the exhaust gas aftertreatment metering valve is actuated during pressure buildup and during run-on. Aeration and ventilation prevent the formation of an air cushion during filling and the formation of a vacuum when the AdBlue® reduction agent is being pumped back. The status is ignition OFF (circuit 15) while the exhaust gas aftertreatment control unit continues to run.
How long the reverse pumping of the AdBlue® reduction agent and filling of the pressure line takes depends on the length of the pressure line.