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

ENGINE 281.910 in MODEL 453.0/3/4 

Function requirements for exhaust treatment, general points 

Exhaust treatment, general 

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

To do this, amongst other things, the catalytic converter must be rapidly brought up to operating temperature in order to reduce the exhaust emissions during cold starts.

Function sequence for exhaust treatment 

The following subsystems are involved in exhaust treatment:

Function sequence for catalytic converter 

The pollutants in the exhaust emitted by the engine are converted chemically by the near-engine mounted catalytic converter (three-way catalytic converter) for λ=1. Through oxidation, carbon monoxide is converted to carbon dioxide (CO2 ) and hydrocarbon to water (H2 O)+ carbon dioxide. Through reduction the nitrogen oxides are converted into nitrogen (N 2 )+ carbon dioxide.

Additional function requirements for secondary air injection (for code (494) USA version) 

Function sequence for secondary air injection (for code 494 (USA version)) 

Secondary air injection more rapidly warms up the firewall catalytic converters to operating temperature after starting and thus improves the exhaust emission values in the warming-up phase. The ME-SFI [ME] control unit (N3/10) manages the secondary air injection according to signals from the following sensors:

Injected air is supplied by the secondary air injection pump (M33), which is actuated through the secondary air injection pump relay (K64I) by the ME-SFI [ME] control unit. If the secondary air injection pump switchover valve (Y32) is actuated by the ME-SFI [ME] control unit at the ground end, it switches through the vacuum from the intake manifold to the exhaust combination valve (secondary air injection). This opens and the injected air is blown from the secondary air injection pump into the outlet ducts of the cylinder head.

IMPORTANT The injected air reacts with the hot gases in the outlet ducts and in the catalytic converter. Oxidation of carbon monoxide (CO) and hydrocarbons (HC) takes place (afterburning). The afterburning causes an increase in the exhaust temperature (exothermic reaction), which also heats up the catalytic converter. To provide secondary air injection, the secondary air pump switchover valve and the secondary air injection pump are actuated simultaneously by the ME-SFI [ME] control unit for up to 43 s (35 s exhaust open and 8 s pressure) following engine start. After actuation of secondary air injection, it is prevented from reoccurring until the coolant temperature has risen to > 60°C and then drops again to below < 30°C. The secondary air injection pump also has sufficient time to cool down again.

IMPORTANT The secondary air injection may be released for diagnosis using Xentry Diagnostics for a max. of 120 s (a shorter period on a warm engine). Prior to the next actuation, it is essential to maintain a cooling time of 30 minutes, otherwise the secondary air injection pump may be damaged (overheated).

View of engine from the front (shown with code 494 (USA version)) 

G12094558Courtesy of MERCEDES-BENZ USA

Additional function requirements for upshift delay (for code 429 (twinamic)) 

Function sequence for upshift delay (for code 429 (twinamic)) 

The upshift delay brings the CAT downstream of the engine start more rapidly up to operating temperature. The ME-SFI [ME] control unit controls the upshift delay according to the following sensor and signal:

Upshift delay is active for a maximum of 160 s and is entirely electronic. The ME-SFI [ME] control unit sends a request via the drive train CAN (CAN C) to the dual-clutch transmission control unit (N1513) (for code 429 (twinamic)), to move the shift lines. 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 

Function sequence for monitoring the catalytic converter efficiency 

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

The purpose of monitoring the catalytic converter efficiency is to use the oxygen storage capacity of the firewall catalytic converter to determine the degree of aging, and therefore the degree of pollutant conversion (conversion).

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

IMPORTANT The oxygen stored during the "lean operating phase" is reduced totally or partially during the "rich operating phase". Aging reduces the oxygen storage capacity and pollutant conversion capacity of the catalytic converter. Because the catalytic converter has a high ability to store oxygen, the alteration of the oxygen content in line with the catalytic converter is fully dampened. Consequently, the oxygen sensor signal downstream of the catalytic converter has a low amplitude and is virtually constant.

When the catalytic converter is at operating temperature and the lambda control enabled, the amplitude variables of the oxygen sensor signals downstream and upstream of the catalytic converter are compared.

If the catalytic converter is no longer operable, the oxygen sensor signal of the oxygen sensor upstream of the catalytic converter and the oxygen sensor signal of the oxygen sensor downstream of the catalytic converter are the same.

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. The engine diagnosis indicator lamp (A1e58) in IC (A1) (for code K35 (IC with monochrome display)) or (for code K36 (IC with a colored 8.9 cm (3.5") display)) is actuated by the ME-SFI [ME] control unit via the interior CAN for fault detection.

Any faults detected are stored in the fault memory of the ME-SFI [ME] control unit. These can be read out and deleted using a diagnostic unit.

View of engine from the rear left (shown with code 494 (USA version)) 

G12094559Courtesy of MERCEDES-BENZ USA
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