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P208B




DTC P208B

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptors
DTC P208B
- Reductant Pump Performance

Diagnostic Fault Information





Circuit/System Description

The selective catalytic reduction (SCR) system reduces oxides of nitrogen (NOx) emissions by injecting a metered amount of diesel exhaust fluid (DEF) or reductant into the exhaust gas stream entering the SCR catalyst. Within the SCR catalyst, the DEF reacts with the NOx to form nitrogen, carbon dioxide, and water vapor. Upstream and downstream NOx sensors provide the engine control module (ECM) with engine-out and tailpipe-out NOx levels. The ECM varies the amount of DEF added by varying the reductant injector duty cycle in response to changes in engine-out NOx levels.

The ECM supplies system voltage to the reductant pump motor. The ECM controls the solenoid by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled-up to a voltage. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage. The ECM supplies a ground to the low reference circuit. As the duty-cycle increases, the output of the reductant pump increases.

Conditions for Running the DTCs

* The engine speed is greater than 600 RPM.
* The engine run time is greater than 10 s.
* The reductant remaining defrost time is less than 120 s.
* The reductant motor operating for greater than 2 s.
* The BARO is greater than 75 kPa (11 psi).
* The emission reduction fluid tank is not empty.
* The ambient air and the emission reduction fluid tank is warmer than -7°C (19°F).
* The DTC runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the commanded state of the reductant pump driver and the actual state of the control circuit do not match for greater than 10 s.

Action Taken When the DTC Sets

DTCs P208B is a Type B DTC.

Conditions for Clearing the DTC

DTCs P208B is a Type B DTC.

Diagnostic Aids

A leak in the reductant system can be located by inspecting for a build-up of crystallized diesel exhaust fluid (DEF).

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

* Diesel Exhaust Fluid (DEF) Warning Strategy Service Precautions
* Exhaust Aftertreatment System Description (Emission Control Systems)

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information

Circuit/System Verification

Note: Diesel exhaust fluid (DEF) that is frozen could cause this DTC to set.

1. Ignition ON, observe the DTC information with a scan tool. DTC P204B, P204C, P204D, or P207F should not be set.

• If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) for further diagnosis.

2. Engine idling until EGT Sensor 2 is greater than 170°C (338°F). Observe the scan tool Reductant Pressure Sensor parameter. The reading should be between 425-575 kPa.
3. Observe the scan tool Reductant Pump Control Circuit Status parameter. The parameter should display OK or Not Run.
4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Verify the following conditions do not exist:

* Contaminated diesel exhaust fluid-Refer to Contaminants-in-Diesel Exhaust Fluid Diagnosis (Contaminants-in-Diesel Exhaust Fluid Diagnosis)
* Missing, restricted, or leaking reductant components
* Restricted or plugged Q62 reductant purge valve - Stuck closed
* High resistance in the G33 reductant pump motor or Q62 reductant purge valve circuits
* Inspect the harness connectors and the ground circuits of the DEF tank for poor connections.

• If a condition is found, repair as necessary.

2. Command the Reductant System Leak Test ON with a scan tool. Allow the pressure to build for 30 s. Verify there are no leaks in the reductant lines.

• If a condition is found, repair as necessary.

3. Remove the Q61 emission reduction fluid injector from the exhaust pipe leaving the reductant line and electrical connector connected. Place the Q61 emission reduction fluid injector into a suitable container.
4. Ignition ON, command the Reductant System Leak Test ON with a scan tool. Allow the pressure to build for 30 s. The Q61 emission reduction fluid injector should not leak.

• If a condition is found, replace the Q61 emission reduction fluid injector.

5. Ignition OFF, disconnect the 24-way harness connector at the DEF Tank. Refer to Inline Harness Connector End Views (Connector End Views By Number) for connector identification.

Note: Testing for steps 2-5 is performed on the ECM side of the harness connector.

6. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 5 ohm between the low reference circuit terminal C6 and ground.

• If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

7. Ignition ON, test for B+ between the reductant pump motor supply voltage circuit terminal A6 and ground.

• If less than the specified range, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

8. Test for 2.5-4.5 V between the reductant pump motor control circuit terminal B6 and ground.

• If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.
• If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.

9. Connect a test lamp between the reductant pump motor control circuit terminal B6 and the reductant pump motor supply voltage circuit terminal A6. Command the Reductant Pump to 80 percent with a scan tool. The test lamp should illuminate or flash when commanded to 80 percent.

• If the test lamp does not illuminate or flash, replace the K20 ECM.

Note: Testing for this step is performed on the DEF tank side of the harness connector.

10. Remove the DEF tank and test, inspect, and repair the items listed below. If all items test normal, replace the G33 reductant pump motor.

* Poor connection at the 24-way harness connector
* Open or shorted DEF smart pump supply voltage circuit
* Open or shorted DEF smart pump control circuit
* Open DEF smart pump low reference circuit

Repair Instructions

* Emission Reduction Fluid Tank Replacement (Emission Reduction Fluid Tank Replacement)
* Perform the scan tool Reductant System Reset procedure after replacing the emission reduction fluid tank.
* Control Module References (Programming and Relearning)for engine control module replacement, programming, and setup

Repair Verification

1. Install any components or connectors that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
3. Clear the DTCs.
4. Ignition OFF, all vehicle systems OFF, this may take up to 2 minutes.

Note: The diesel exhaust fluid (DEF) and ambient air temperatures must be greater than -7°C (19°F) before proceeding with this procedure.

5. Ignition ON, command the Reductant System Leak Test ON with a scan tool. Allow the pressure to build for 30 s. Observe the scan tool Reductant Pressure sensor parameter. The reading should be between 425-575 kPa and there should be no leaks in the system.

Warning

Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

6. In order to clear the DEF lamp, idle the engine at operating temperature for 15 minutes. Accelerate at part throttle to 32-48 km/h (20-30 mph) for up to 5 minutes or until the DEF lamp turns OFF. The DEF lamp should turn OFF.

• If the DEF lamp does not turn OFF, a condition with the system still exists.

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