Exhaust Treatment Function - GF14.00-P-3000MMV

Engine 276.8 in model 205, 253 

Function requirements for exhaust treatment, general points 

• Circuit 87M (Engine management ON)
• Engine runs

Exhaust treatment, general 

The task of exhaust treatment is to reduce the exhaust emissions:

• Nitrogen oxides (NOx)
• Hydrocarbon (HC)
• Carbon monoxide (CO)

To do this, amongst other things, the catalytic converters (three-way catalytic converters) must be rapidly brought up to operating temperature in order to reduce the exhaust emissions for a cold start.

Function sequence for exhaust treatment 

The following subsystems are involved in exhaust treatment:

• Function sequence for catalytic converters 
• Function sequence for upshift delay 
• Function sequence for monitoring the catalytic converter efficiency 

Function sequence for catalytic converters 

The pollutants emitted by the engine are converted chemically at λ=1 by the catalytic converters (three-way catalytic converters).

Through oxidation, carbon monoxide is converted to carbon dioxide (CO ₂ ) and hydrocarbon to water (H₂ O)+ carbon dioxide.

Through reduction the nitrogen oxides are converted into nitrogen (N₂ )+ carbon dioxide.

Additional function requirements for upshift delay 

• Coolant temperature for a start < 35°C:
• Vehicle speed <40 km/h

Function sequence for upshift delay 

The upshift delay is designed to warm up the catalytic converters to operating temperature more rapidly after the engine has started.

The ME-SFI [ME] control unit (N3/10) controls the upshift delay depending on the following sensor and signal:

• Coolant temperature sensor (B11/4)
• Electronic Stability Program control unit (N30/4), wheel speed via suspension FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1)

The upshift delay is active for a maximum of 60 s and exclusively occurs electronically.

The ME-SFI [ME] control unit makes a request to the fully integrated transmission control unit (Y3/8n4) via drive train CAN to move the shift characteristic curves.

Partial load gear shifts (1-2-1, 2-3-2) thus take place at higher engine speeds or at higher vehicle speeds.

Additional function requirements for monitoring the catalytic converter efficiency 

• Catalytic converters at normal operating temperature
• Lambda control released

Function sequence for monitoring the catalytic converter efficiency 

Hydrocarbon (HC) emissions must not exceed the limit specified by the legal requirements.

The task of the catalytic converter efficiency monitoring function is to determine the aging of the catalytic converters and thus their HC conversion based on their oxygen storage capability.

The ME-SFI [ME] control unit reads in the following signals to monitor the catalytic converter efficiency:

• LH and RH oxygen sensor, sensor elements upstream of catalytic converter (G3/3b1, G3/4b1), oxygen and nitrogen contents
• LH and RH oxygen sensor, sensor elements downstream of catalytic converter (G3/5b1, G3/6b1), oxygen and nitrogen contents
• Crankshaft Hall sensor (B70), engine rpm

The oxygen stored during the "lean operating phase" is reduced totally or partially during the "rich operating phase". With aging, the oxygen storage capacity of the catalytic converters is reduced, and thus also HC conversion.

Changes in the oxygen content downstream of the catalytic converters are almost completely dampened by the high oxygen storage capacity of the catalytic converters.

Consequently, the signals from the oxygen sensors downstream of the catalytic converters have low amplitude and are virtually constant. When catalytic converters are at operating temperature and the lambda control is enabled, the signal amplitudes of the oxygen sensors upstream of the catalytic converters are compared with those downstream.

If the catalytic converters are no longer functional, then the oxygen sensor signals of the sensor elements for the oxygen sensors upstream of the catalytic converter and the oxygen sensor signals of the sensor elements for the oxygen sensors downstream of the catalytic converter are the same magnitude.

A number of measurements take place in the lower partial-load range in the specified rpm range. The results are compared with a characteristics map in the ME-SFI [ME] control unit.

If a fault is detected, the ME-SFI [ME] control unit actuates the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1) via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit (N73) and the user interface CAN (CAN HMI).

Any faults detected are stored in the fault memory of the ME-SFI [ME] control unit. These can be read out and deleted with Mercedes' Xentry Diagnostics.

	Electrical function schematic for exhaust treatment		PE14.00-P-2051-97FBB
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MMV