4B6A - P2201 (DDE)

4B6A - P2201

Information saved in
DDE

Fault code
4B6A - P2201

Fault text
DDE: Nitrogen oxide sensor before SCR catalytic converter,
plausibility: NOx signal dynamically too slow during
traction-overrun transition

Fault description
Dynamic monitoring of NOx sensor before the SCR
converter. The dynamic monitoring function evaluates the
temporal progression of the NOx signal during the transition
from acceleration to overrun. With an intact sensor the time
constant should not be greater than 7 s.
Once trailing throttle/overrun is detected, the monitoring
function proceeds through the following sequence:
A timer starts when the NOx concentration rises above the
first threshold defined according to operating point, which
corresponds to 30% of the anticipated drop in NOx
concentration.
The timer stops when the NOx concentration rises above the
second threshold defined according to operating point,
representing 60% of the expected level of NOx
concentration.
A sensor dynamics error is logged if the NOx sensor is
unable to attain the second threshold value after 7 s elapses.
A sensor dynamics error is also logged when 9 s elapses
without the second threshold value being exceeded.

Condition for fault identification
Test condition:
The test routine runs when the following conditions are
satisfied:
- Dynamic testing enabled.
- The status of the NOx sensors is valid.
- No diagnostic trouble codes have been logged for the NOx
sensor and EGR.
Once these general conditions are satisfied the state machine
function starts, provided that:
- engine rpm is greater than 1650 1/min.
- the injection quantity is greater than
Exh_qThreshChkDynNSCDs_C.
- the shift in the NOx concentration is greater than 80 ppm.
To ensure recognition of a valid load/overrun transition, the
injection quantity must now, within a period of 2 s, fall to a
value below the threshold 1 mg/hub.
Once compliance with these conditions is present a valid
load/overrun transition is recognized and the monitoring
function is enabled.
Voltage condition:
The test routine runs when the following conditions are
satisfied:
- Dynamic testing enabled.
- The status of the NOx sensors is valid.
- No diagnostic trouble codes have been logged for the NOx
sensor and EGR.
Once these general conditions are satisfied the state machine
function starts, provided that:
- engine rpm is greater than 1650 1/min.
- the injection quantity is greater than
Exh_qThreshChkDynNSCDs_C.
- the shift in the NOx concentration is greater than 80 ppm.
To ensure recognition of a valid load/overrun transition, the
injection quantity must now, within a period of 2 s, fall to a
value below the threshold 1 mg/hub.
Once compliance with these conditions is present a valid
load/overrun transition is recognized and the monitoring
function is enabled.

Condition for fault memory entry
Event debounced (1)

Action in service
1. Delete the DTC if the error frequency is 1.
2. Respond to multiple occurences of this error by replacing
the pre-SCR-cat NOx sensor.

Fault effect and breakdown warning
-

Driver information
Warning light:
MIL

Service instruction
-