P0420

4B91 - P0420

Information saved in
DDE

Fault code
4B91 - P0420

Fault text
Oxidation catalytic converter, plausibility: Hydrocarbon
conversion rate during exothermic reaction too low

Fault description
Monitoring of the oxidation catalyst in warmup mode. The
DTC is logged when the calculated conversion rate lies
below the limit value 0.

Condition for fault identification
Test condition:
The monitoring routine executes when the following
conditions are satisfied:
- No other DTCs are logged.
- The oxidation catalyst's surface temperature is above the
minimum limit value 120 �C.
- The oxidation catalyst surface temperature's gradient is
above the minimum limit value OxiCat_dtSurfRHUMin_C.
- Engine running.
- The quantity of fuel consumed since the last particulate
filter regeneration is below the threshold 328 l.
- Temperature model is sufficiently precise: Difference
between the measured and modeled temperatures behind the
oxidation catalyst is less than 500 �C.
- No calculation of HC conversion rate and no monitoring
have taken place in this driving cycle.
- Mass flow rate lies above the threshold 0 kg/h.
Conditions for aborting the process: The test is executed
provided that none of the following conditions lead to
mandatory cancellation:
- Enable conditions are satisfied.
- Warmup mode active for less than maximum threshold
(maximum threshold between 20 sec. at 0 �C and 300 sec. at
200 �C and above). The time is reset when the HC
conversion-rate calculation is not enabled or when a change
in operating mode affecting assessment of the HC
conversion rate is detected.
Trigger condition: The diagnostic routine executes one time
only after the following conditions are satisfied:
- Cumulative exhaust-gas mass flow rate during the
monitoring is less than OxiCat_dmEGAvrgMax_C.
Generation of a cumulative current exhaust-gas mass flow
rate continues for as long as monitoring remains enabled.
Trigger:
- Cumulative HC quantity during the oxidation catalyst's
warmpup phase is above 2 g. Generation of a cumulative
current exhaust-gas mass flow rate continues for as long as
the HC conversion rate calculation remains enabled.
- Oxidation catalyst's surface temperature lies above -
3550 �C.
Once all conditions are satisfied the error is checked one
time with the positive flank.
Voltage condition:
The monitoring routine executes when the following
conditions are satisfied:
- No other DTCs are logged.
- The oxidation catalyst's surface temperature is above the
minimum limit value 120 �C.
- The oxidation catalyst surface temperature's gradient is
above the minimum limit value OxiCat_dtSurfRHUMin_C.
- Engine running.
- The quantity of fuel consumed since the last particulate
filter regeneration is below the threshold 328 l.
- Temperature model is sufficiently precise: Difference
between the measured and modeled temperatures behind the
oxidation catalyst is less than 500 �C.
- No calculation of HC conversion rate and no monitoring
have taken place in this driving cycle.
- Mass flow rate lies above the threshold 0 kg/h.
Conditions for aborting the process: The test is executed
provided that none of the following conditions lead to
mandatory cancellation:
- Enable conditions are satisfied.
- Warmup mode active for less than maximum threshold
(maximum threshold between 20 sec. at 0 �C and 300 sec. at
200 �C and above). The time is reset when the HC
conversion-rate calculation is not enabled or when a change
in operating mode affecting assessment of the HC
conversion rate is detected.
Trigger condition: The diagnostic routine executes one time
only after the following conditions are satisfied:
- Cumulative exhaust-gas mass flow rate during the
monitoring is less than OxiCat_dmEGAvrgMax_C.
Generation of a cumulative current exhaust-gas mass flow
rate continues for as long as monitoring remains enabled.
Trigger:
- Cumulative HC quantity during the oxidation catalyst's
warmpup phase is above 2 g. Generation of a cumulative
current exhaust-gas mass flow rate continues for as long as
the HC conversion rate calculation remains enabled.
- Oxidation catalyst's surface temperature lies above -
3550 �C.
Once all conditions are satisfied the error is checked one
time with the positive flank.

Condition for fault memory entry
Event debounced (1)

Action in service
Replace oxidation catalyst/particulate filter.

Fault effect and breakdown warning
-

Driver information
Warning light:
MIL

Service instruction
none