Exhaust treatment function - GF14.00-P-3000MMW

ENGINE 276.9 in MODEL 212.095 as of model year 2014 

Function requirements for exhaust treatment, general points 

• Circuit 87M (engine timing ON)
• Engine running

The function requirements "internal combustion engine running" includes all function sequences of the fuel low pressure and high-pressure circuit, as described in the function "fuel supply".

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 converter 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 transmission shift delay 
• Function sequence for monitoring the catalytic converter efficiency 

Function sequence for catalytic converters 

The pollutant in the exhaust emitted by the engine are converted chemically by the near-engine mounted catalytic converters (three-way catalytic converters) for λ=1 (converted). Through oxidation, carbon monoxide is converted to carbon dioxide (CO₂ ) and hydrocarbon into water (H₂ O)+ carbon dioxide.

Additional function requirements for transmission shift delay 

• Coolant temperature at start < 35°C
• Vehicle speed <40 km/h

Function sequence for transmission shift delay 

The transmission shift delay is designed to warm up the catalytic converters more rapidly to operating temperature after engine start.

The ME-SFI [ME] control unit controls the transmission shift delay according to the following sensor and signal:

• Coolant temperature sensor (B11/4)
• Regenerative braking system control unit (N30/6), wheel speed via chassis CAN 1 (CAN E1)

Transmission shift delay is active for a maximum of 60 s and is entirely electronic. The ME-SFI [ME] control unit makes a request to the fully integrated transmission control unit (Y3/8n4) via the drive train CAN (CAN C) to shift 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 enabled

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 sensors to monitor the catalytic converter efficiency:

• Left and right oxygen sensor elements upstream of catalytic converter (G3/3b1, G3/4b1)
• Left and right oxygen sensor elements downstream of catalytic converter (G3/5b1, G3/6b1)
• Crankshaft Hall sensor (B70), engine speed

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 sensor elements downstream of the catalytic converters have low amplitude and are virtually constant. For catalytic converters at a normal operating temperature and released lambda control the sizes of the amplitude of signals for oxygen sensor elements downstream and upstream of the catalytic converters are compared. If the catalytic converters are no longer ready to operate then the signals from the oxygen sensor element upstream of the catalytic converter and the signals from the oxygen sensor element downstream of the catalytic converter are the same size. A number of measurements take place in the lower partial-load range in the specified engine rpm range. The results are compared with a characteristic map in the ME-SFI [ME] control unit. For fault detection a signal is sent to the front SAM control unit with fuse and relay module (N10/1) from the ME-SFI [ME] control unit via the chassis CAN 1 (CAN E1). The front SAM control unit with fuse and relay module transmits the signal further via the suspension CAN 2 (CAN E2) and this actuates the engine diagnosis indicator lamp (A1e58) in IC (A1). Any faults detected are stored in the fault memory of the ME-SFI [ME] control unit. These can be read out and deleted with Xentry Diagnostics.