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

ENGINE 276.8 in MODEL 207, 212 as of model year 2014 

ENGINE 276.8 in MODEL 218 as of model year 2015 

ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 as of model year 2014 

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 firewall 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 firewall catalytic converters 
• Function sequence for NOx storage catalytic converter (with code (920) Gasoline direct injection with stratified charge) 
• Function sequence for upshift delay 
• Function sequence for monitoring the catalytic converter efficiency 

Function sequence for firewall catalytic converters 

The pollutants in the exhaust emitted by the engine are converted chemically by the near-engine mounted firewall catalytic converters (three-way catalytic converters) for λ=1.

Through oxidation, carbon monoxide is converted to carbon dioxide (CO₂ ) and hydrocarbon to water (H2O)+ carbon dioxide.

Through reduction the nitrogen oxides are converted into nitrogen (N ₂ )+ carbon dioxide.

Function sequence for NOx storage catalytic converter (with code (920) Gasoline direct injection with stratified charge) 

For engine 276.8 there is a NOx storage catalytic converter and for engine 276.9 two NOx storage catalytic converters installed. The function sequence is identical and is described for a NOx storage catalytic converter.

In homogeneous operation with λ=1 the pollutants hydrocarbon, carbon monoxide and nitrogen oxide are also converted in the firewall catalytic converters with the support of the NOx storage catalytic converters.

In homogeneous operation the limits of the nitrogen oxides are maintained by the firewall catalytic converters and the lambda control.

In stratified operation with λ>1, the nitrogen oxides are stored in the NOx storage catalytic converters as a result of a chemical reaction. If the storage capability is exhausted, the stored nitrogen oxides must be converted into nitrogen and carbon dioxide by purging the NOx storage catalytic converter.

Purging of NOx storage catalytic converter 

The fuel-saving stratified operation can only be enabled when the increasing amounts of nitrogen oxides in the NOx storage catalytic converter have been converted.

The ME-SFI [ME] control unit (N310) reads in the following sensors and signals for purging of the NOx storage catalytic converter:

• Temperature sensors upstream of the RH and LH NOx storage catalytic converter (B16, B16/1), exhaust temperatures
• Left and right NOx sensors (N37/5b1, N37/6b1), nitrogen oxide and oxygen components in the exhaust over the left and right NOx sensor control units (N37/5, N37/6) and via the drive train sensor CAN (CAN I) (for engine 276.9)
• Left and right NOx sensors upstream of the NOx storage catalytic converter (N37/9b1, N37/10b1), nitrogen oxide and oxygen components in the exhaust over the left and right NOx sensor control units upstream of the NOx storage catalytic converter (N37/9, N37/10) and via the drive train sensor CAN (CAN I) (for engine 276.8)
• NOx sensors downstream of the NOx storage catalytic converter (N37/11b1), nitrogen oxide and oxygen components in the exhaust over the NOx sensor control unit downstream of the NOx storage catalytic converter (N37/11) and the drive train sensor CAN (CAN I) (for engine 276.8)

The ME-SFI [ME] control unit uses the NOx sensor to detect any abrupt increase in NOx, which indicates that the NOx storage catalytic converter is full. Homogeneous operation is activated as a reaction to this and the mixture enriched, so that the NOx storage catalytic converter can regenerate.

Stratified operation is then activated again.

For NOx conversion a temperature range of 250 to 500 °C in the NOx storage catalytic converter is optimal. For stratified operation or wide open throttle it must not get hotter than approx. 800°C.

The exhaust temperature is monitored by a temperature sensor in every strand of the exhaust system. The temperature sensors determine the current exhaust temperatures and lead these in the form of voltage signals for evaluation to the ME-SFI [ME] control unit.

Mixture formation is used to regulate the temperature of the NOx storage catalytic converter. The mixture formation is adapted on the basis of the stored temperature models in order to protect the NOx storage catalytic converter against excessively high temperatures.

In order to convert all pollutants in the exhaust, sulfur-free fuel is required. Sulfur blocks the spaces for nitrogen oxides in the NOx storage catalytic converter, resulting in fewer nitrogen oxides being stored. Stratified operation is therefore shortened and purging must be performed more frequently.

Additional function requirements for upshift delay 

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

Function sequence for upshift delay 

The upshift delay brings the firewall catalytic converter more quickly up to operating temperature after the engine start. The ME-SFI [ME] control unit controls the upshift delay dependent on the following sensor and signal:

• Coolant temperature sensor (B11/4) (model 207, 212) or coolant temperature sensor (B11/4) (model 218)
• Electronic Stability Program control unit (N30/4) (except code 233 (DISTRONIC PLUS) or Electronic Stability Program Premium control unit (N30/7) (for code 233 (DISTRONIC PLUS), wheel speed via chassis CAN 1 (CAN E1)

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

The ME-SFI [ME] control unit makes the request via the drive train CAN (CAN C) to the fully integrated transmission control controller unit (Y3/8) to move the shift characteristics. 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 

• Firewall catalytic converters at 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 firewall 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 sensors upstream of catalytic converter (G3/3, G3/4)
• Left and right oxygen sensors downstream of catalytic converter (G3/5, G3/6)
• 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 firewall catalytic converters is reduced, and so therefore is HC conversion.

Changes in the oxygen content downstream of the firewall catalytic converters are almost completely dampened by the high oxygen storage capacity of the firewall catalytic converters. Consequently, the signals from the oxygen sensors downstream of firewall catalytic converters have low amplitude and are virtually constant.

When firewall catalytic converters are at operating temperature and the lambda control is enabled, the signal amplitudes of the oxygen sensor downstream and upstream of the firewall catalytic converters are compared. If the firewall catalytic converters are no longer working effectively, the oxygen sensors signals upstream have the same amplitude as those downstream.

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.

For fault detection the engine diagnosis indicator lamp (A1e58) is actuated by the ME-SFI [ME] control unit in IC (A1) via the chassis CAN 1, front SAM control unit with fuse and relay module (N10/1) and chassis CAN 2 (CAN E2).

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.