(Exhaust Gas Recirculation, Function - GF14.20-P-3000OGR)

ENGINE 642.8 in MODEL 166 up to model year 2016 

Function requirements for exhaust gas recirculation (EGR), general points 

• Circuit 87M (engine management ON)
• Engine runs
• Engine in load range from neutral to the upper partial-load range

Exhaust gas recirculation, general 

The EGR lowers the nitrogen oxide (NOx) portion in the exhaust. This occurs by means of the following 3 processes:

• Reduction of oxygen (O₂ ) concentration in combustion chamber
• Reduction of the combustion temperature through reduction of the combustion speed
• Reduction of the combustion temperature through a higher heat capacity of the recirculated exhaust compared to the intake air

Heat capacity

The heat capacity is a material property and indicates how much heat a substance can store per temperature change.

Function sequence for exhaust gas recirculation 

EGR is active from idle through to the upper partial-load range. Determination of the EGR rate takes place depending on the following variables:

• Engine temperature, engine load and engine rpm
• Ambient conditions such as the air intake or the charge air temperature
• Exhaust temperature
• Diesel particulate filter status (with code (474) Particulate filter)
• Exhaust back pressure
• Time limitation (in idle)
• Boost pressure
• Coolant temperature

For this purpose, the CDI control unit (N3/9) reads signals from the following components:

• Engine oil temperature sensor (B1)
• Left hot film mass air flow sensor (B2/6)
• Left intake air temperature sensor (B2/6b1)
• Right hot film mass air flow sensor (B2/7)
• Right intake air temperature sensor (B2/7b1)
• Boost pressure sensor (B5/1)
• Coolant temperature sensor (B11/4)
• Exhaust gas recirculation temperature sensor (B16/14) (with code U42 (BlueTEC (SCR) diesel exhaust treatment) and code 494 (USA version))
• Charge air temperature sensor (B17/8)
• Temperature sensor upstream of catalytic converter (B19/7) (with code U42 (BlueTEC (SCR) diesel exhaust treatment))
• Temperature sensor upstream of diesel particulate filter (B19/9) (with code 474 (Particulate filter))
• Temperature sensor upstream of ATL (B19/11)
• Pressure sensor downstream of air filter (B28/5)
• DPF differential pressure sensor (B28/8) (with code 474 (Particulate filter))
• Accelerator pedal sensor (B37)
• Actual value potentiometer 1 throttle valve (M16/6r1)
• Exhaust pressure sensor (B60)
• Crankshaft Hall sensor (B70)
• Exhaust gas recirculation cooling bypass flap Hall sensor (B90) (with code U42 (BlueTEC (SCR) diesel exhaust treatment) and code 494 (USA version))

After evaluating the input signals, the CDI control unit uses the stored characteristics map to actuate the exhaust gas recirculation actuator (Y27/9) with a pulse width modulated signal. Depending on its actuation, the exhaust gas recirculation actuator increases or decreases the quantity of recirculated exhaust which is led into the charge air distributor via a mixing tube downstream of the throttle valve actuator (M16/6).

To increase the effect of EGR, the exhaust gas is passed through the exhaust gas recirculation cooler where it is cooled. If the temperature of the recirculated exhaust gas is too low, the recirculated exhaust gas can be guided past the exhaust gas recirculation cooler via a bypass duct.

If the exhaust gas recirculation cooler bypass switchover valve (Y85) is actuated by the CDI control unit by means of a ground signal based on a characteristics map, then the vacuum stored in the vacuum reservoir acts on the exhaust gas recirculation cooler bypass vacuum unit and opens the bypass in the exhaust gas recirculation cooler via a linkage. The exhaust temperature determined by the exhaust gas recirculation temperature sensor is used by the CDI control unit to monitor the cooling function of the exhaust gas recirculation cooler.

For vehicles with code 494 (USA version) the position of the bypass flap (open, closed) is determined via the exhaust gas recirculation cooling bypass flap Hall sensor.

Exhaust emissions standard

Engine 642.8 complies with the EU-5 exhaust emission standards. Vehicles with code U42 (BLUETEC (SCR) diesel exhaust treatment) fulfill the EU-6 exhaust emissions standard or the BIN5 LEVII exhaust emissions standard for the USA.

	Electrical function schematic for exhaust gas recirculation		PE14.20-P-2052-97NAC
	Overview of system components for common rail diesel injection (CDI)		GF07.16-P-9997OGR