Catalytic Converter Efficiency Monitoring Function

Catalytic Converter Efficiency Monitoring Function




Shown on engine 104 (USA)
A1E26 "CHECK ENGINE" MIL
N3/4 HFM-SFI [HFM] control unit
N3/10 ME-SFI control unit
G3/1 O2 sensor downstream of TWC
G3/2 O2 sensor upstream of TWC
X11/4 Data link connector
a Amplitude of O2 sensor signal downstream of TWC
b Amplitude of O2 sensor signal upstream of TWC

Task
Detecting catalytic converters with insufficient efficiency and operating engine diagnosis indictor lamp (EURO3/4) or CHECK ENGINE (USA) (MIL).

Design/function
When the catalytic converter is at operating temperature and the lambda closed-loop control is activated, the O2 sensor signal downstream of TWC is compared with the O2 sensor signal upstream of TWC. The amplitude of the O2sensor voltage downstream of TWC must be less than the amplitude of the O2sensor voltage upstream of TWC (Note: E.g. if no monolith was built into the catalytic converter, the O2sensor signals upstream or downstream TWC would be identical).

The catalytic converter is evaluated on the basis of its ability to store oxygen. Several measurements must be performed in the specified engine speed and load range. The results are compared with a map and a fault is detected in this way.