P21B2

P21B2-EXCESSIVE TIME TO ENTER CLOSED LOOP NOX ABSORBER CONTROL

For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

When the engine runs in DeNOx mode, the Powertrain Control Module (PCM) monitors how much post injection fuel has been injected. Once it exceeds a threshold, the measured O2 Sensor 1/1 is supposed to be lower than a threshold. If after a sufficient amount of post fuel is injected, the O2 Sensor 1/1 value is still high for a calibrated time, the fail counter is incremented by 1. If it is not, it is decremented by 1. If the counter has been incremented or decremented for a calibrated number of times, and the counter value is greater than a calibrated value, this fault is set.

- When Monitored:
With the engine speed above a calibrated threshold for a calibrated time, and ambient air temperature is above a calibrated threshold, and the engine running in DeNOx mode.

- Set Condition:
If during post fuel injection, the O2 Sensor 1/1 value is above a calibrated threshold a fail count is recorded as incremented. If not, it is recorded as decremented. After a calibrated number of total counts (incremented and decremented), the counter value is above a calibrated value, a fault is set.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1.

NOTE: If there are any DTCs present for the MAF Sensor, EGR Valve, EGR Airflow Control Valve, or EGR Cooler Bypass Valve, repair those DTCs before proceeding.
CHECK THE MAF SENSOR
1. Ignition on, engine not running.
2. With the scan tool in Sensors, read the Mass Air Flow sensor.

Does the Mass Air Flow sensor read 0 +/- 2lb/min?

Yes

- Go To 2

No

- Replace the Mass Air Flow Sensor.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

2. CHECK THE EGR AIRFLOW THROTTLE CONTROL VALVE
1. Remove the boot from the EGR Airflow Throttle Control Valve.
2. Using a mirror, look at the butterfly valve on the inside of the EGR Airflow Throttle Control Valve.
3. Start the vehicle, let idle for 10 seconds.
4. Turn the ignition off.

NOTE: If functioning properly the EGR Airflow Throttle Control Valve will cycle closed immediately after the engine is shut down.

Did the EGR Airflow Throttle Control Valve cycle closed immediately after the engine was shut down?

Yes

- Go To 3

No

- Replace the EGR Airflow Throttle Control Valve.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. CHECK THE THERMOSTAT OUTLET
1. Remove the EGR Outlet Temperature Sensor from the thermostat outlet.

Is the outlet free of debris?

Yes

- Go To 4

No

- Remove debris from outlet.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

4. CHECK FOR EGR CROSSOVER TUBE RESTRICTION
1. Remove EGR Crossover tube from EGR Cooler and EGR Valve.
2. Inspect tube for restriction.

Is the EGR crossover tube restricted?

Yes

- If possible, clean the tube. If not, replace the tube.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 5

5. CHECK THE EGR VALVE
1. Check the EGR Valve for binding or excessive soot build up.

Were any problems found?

Yes

- Clean or replace the EGR Valve.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 6

6. CHECK FOR EGR COOLER FOULING
1. Remove and clean the EGR Cooler with approved Mopar EGR System cleaner.
2. Reinstall the EGR Cooler.
3. With the scan tool, erase DTCs.
4. Turn the ignition off for 75 seconds.
5. Start the engine. It may be necessary to test drive the vehicle.

Is there a one trip fault logged against DTC P21B2?

Yes

- Replace the EGR Cooler.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 7

7. CHECK THE INJECTOR RETURN FLOW
1. Injector Return Flow Test Perform the INJECTOR RETURN FLOW TEST.

Does the injector drainage meet the test specification?

Yes

- Replace the NOx Absorbing Catalyst.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Repair cause of high Fuel Injector leakage.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.