GF49.10-P-3033MAR Monitoring Catalytic Converter Efficiency, Function

GF49.10-P-3033MAR Monitoring Catalytic Converter Efficiency, Function
ENGINE 156.981 in MODEL 230.470 as of Model Year 09 /Modification Year 08 model refinement package

Function requirements for monitoring catalytic converter efficiency, general points
^ Circuit 87M ON (engine control ON)
^ Engine running
^ Firewall catalytic converters at operating temperature
^ Lambda control enabled

Monitoring catalytic converter efficiency, general points
By law, HC emissions must not go above certain limits.
The purpose of monitoring the catalytic converter efficiency is to evaluate the oxygen storage capacity of the firewall catalytic converters in order to obtain an indication of aging, and therefore of HC conversion.

For this purpose, the ME-SFI control unit (N3/10) reads the following sensors:

- Crankshaft Hall sensor (B70), motor speed
- LH and RH O2 sensors upstream of CAT (G3/3, G3/4)
- LH and RH O2 sensors downstream of CAT (G3/5, G3/6)

The oxygen stored during the "lean operating phase" is then reduced totally or partially during the "rich operating phase". With aging, the oxygen storage capacity of firewall catalytic converter 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.
This results in the O2 sensor signal downstream of the firewall catalytic converters being virtually constant with a small amplitude.

Monitoring catalytic converter efficiency, function sequence
When the firewall catalytic converter is operationally warm and lambda control enabled, the amplitude sizes of the O2 sensor signals downstream and upstream of the firewall catalytic converters are compared.
If the firewall catalytic converters are no longer functional, the O2- sensor signals from the O2 sensors upstream of CAT are at the same amplitude as the O2 sensor signals from the O2 sensors downstream of CAT.

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

Any faults detected are stored in the fault memory of the ME-SFI control unit.
These can be read out and deleted with the DAS system.

If a fault is detected, the ME-SFI control unit actuates the engine diagnosis indicator lamp (A1e58) through the engine compartment CAN (CAN C) or, with code (494) USA version, the CHECK ENGINE indicator lamp (A1e26) on the instrument cluster (A1).