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P20EE






P20EE-SCR NOx CATALYST EFFICIENCY BELOW THRESHOLD - BANK 1

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

Theory of Operation

The Selective Catalytic Reduction (SCR) Catalyst is used in combination with the Diesel Exhaust Fluid system to reduce the amount of NOx gases produced during engine combustion. Excessive fuel or oil entering the exhaust system due to a failed engine component or Fuel Injector can cause the temperature to rise and will result in damage to the SCR Catalyst. The Powertrain Control Module (PCM) monitors the NOx concentration in the engine's exhaust gases using an aftertreatment Intake NOx Sensor and an aftertreatment Outlet NOx Sensor. By comparing these two values, the PCM is able to determine the conversion efficiency of the SCR catalyst and dosing system. The PCM illuminates the MIL immediately when the monitor runs and fails.

- When Monitored:
This monitor has to meet specific engine and aftertreatment conditions to run and complete. NOx sensor data is gathered over varying engine speeds and loads. When enough data has been gathered, the diagnostic will run, make a pass/fail decision, and begin to gather data again.

- Set Condition:
The Powertrain Control Module detects that the NOx conversion across the SCR catalyst is lower than expected.





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

1. ACTIVE DTC

NOTE: Troubleshoot all other active NOx Sensor and DEF Dosing System related fault codes before this fault.

1. Turn the ignition on.
2. With the scan tool, select View DTCs.

Is the DTC active?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION - 6.7L diagnostic procedure. . Intermittent Condition Test

2. CHECK THE DIESEL EXHAUST FLUID
1. Turn the ignition off.
2. Collect a sample of diesel exhaust fluid from the system.
3. Visually inspect the fluid for signs of contamination or debris.
4. Test the quality of the fluid using litmus paper (supplied by parts) or by using the SPX DEF/UREA Refractometer 94-F-00K-108-456 or equivalent.

NOTE: The diesel exhaust fluid should register approximately 9 ph with the litmus paper and 32.5 percent using a refractometer.

Is the diesel exhaust fluid quality within specification and free of debris and contamination?

Yes

- Go To 3

No

- Drain the diesel exhaust fluid from the tank and fill the system. If the fluid is contaminated, follow the cleaning procedure. Procedures.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. CHECK FOR DIESEL EXHAUST FLUID LEAK
1. Turn the ignition on.
2. With the scan tool, navigate to Systems Tests and actuate the DEF Prime Test.

NOTE: This will pressurize the system, making a leak easier to see.

3. Inspect for signs of a Diesel Exhaust Fluid leak at:
- DEF Tank connectors.
- DEF Injector and Injector connectors.
- DEF Heater Lines.
- DEF Supply Pump Assembly.

NOTE: Diesel exhaust fluid will form white deposits around leaky fittings.

Were any leaks found?

Yes

- Repair or replace the faulty component.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 4

4. CHECK THE EXHAUST SYSTEM FOR LEAKS
1. Visually inspect the entire exhaust system for signs of a leak.

Were any exhaust leaks found?

Yes

- Perform the appropriate repair.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 5

5. CHECK FOR DEPOSITS IN THE DECOMPOSITION TUBE
1. Remove the DEF Injector from the Decomp Tube. Diesel Exhaust Fluid Injector - Removal.
2. Visually inspect the Decomp Tube for diesel exhaust fluid deposits.

Were any deposits found?

Yes

- Clean the deposits from the Decomp Tube.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 6

6. CHECK THE DEF INJECTOR OPERATION
1. Reconnect the DEF Injector harness connector.
2. Place the DEF Injector in a container to capture the fluid sprayed.
3. Turn the ignition on.
4. With the scan tool, navigate to Systems Tests and actuate the Diesel Exhaust Fluid Doser Pump Override Test.

NOTE: This Test will run for six minutes before timing out. The amount of flow may fluctuate through out the test, therefore the test must be allowed to run completely in order for the results to be accurate. The fluid should spray out as a mist. There should be no dripping from the holes in the DEF Injector at any time during the duration of the test procedure.

5. Measure the amount of fluid sprayed after the test times out

Does the fluid sprayed measure between 85 ml and 115 ml?

Yes

- Replace the SCR Catalyst. Selective Catalytic Reduction (SCR) Catalyst - Removal.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Replace the DEF Supply Pump Assembly Filter, Diesel Exhaust Fluid Filter - Removal. Perform the Diesel Exhaust Fluid Doser Pump Override Test again. If the system passes, then the repair is complete. If the system fails the test again, replace the DEF Supply Pump Assembly. Diesel Exhaust Fluid Pump Assembly - Removal.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

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