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Tahoe / Yukon Service Manual

DTC P2C7A

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5509066 Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. DTC Descriptor DTC P2C7A Nitrogen Oxides Catalytic Converter 2 Efficiency Below Threshold Circuit/System Description For an overview of the component/system, refer to: Exhaust Aftertreatment System Description The diesel exhaust aftertreatment system consists of an under hood catalyst and an underbody catalyst. The under hood catalyst consists of the main Diesel Oxidation Catalyst and the coated Diesel Particulate Filter (DPF). The Underbody catalyst contains the secondary selective catalytic reduction (SCR). One of the main purposes of the DPF is to collect particulates from the engine exhaust in order to minimize discharge of soot to the atmosphere. The SCR system reduces oxides of nitrogen (NOx) emissions by injecting a metered amount of diesel exhaust fluid or reductant into the exhaust gas stream entering the SCR. Within the selective catalytic reduction catalyst, the reductant reacts with the NOx to form nitrogen, carbon dioxide, and water vapor. Three smart NOx sensors provide the engine control module (ECM) with engine-out and tailpipe- out NOx levels. The ECM uses two (NOx) sensors to control exhaust NOx levels. he first NOx sensor is located at the turbocharger outlet and monitors the engine out NOx. The second NOx sensor is located in the exhaust pipe downstream of the SCR. and monitors NOx levels exiting the close coupled SCR. The third NOx sensor is located in the exhaust pipe downstream of the rear SCR and monitors NOx levels exiting the aftertreatment system. The smart NOx sensors communicate with the ECM over the serial data line. Conditions for Running the DTC DTC P2C7A DTC P200C, P202E, P2BAA, P30B5, U029D, U029E, U02A1 = Not set DTCs related to the following system/component = Not Set – B9 Ambient Air Temperature Sensor – B17 Barometric Pressure Sensor – B26 Crankshaft Position Sensor – B34 Engine Coolant Temperature Sensor – B65 Intake Manifold Pressure and Air Temperature Sensor – B75C Multifunction Intake Air Sensor – B115 Vehicle Speed Sensor – B131 Exhaust Temperature Sensor – B154 Diesel Particulate Filter Exhaust Differential Pressure Sensor – B195 Nitrogen Oxides Sensor – B345R Exhaust Pressure Differential Sensor - Exhaust Gas Recirculation – K115 Reductant Control Module – M103 Turbocharger Vane Position Actuator – M122 Exhaust Pressure Control Valve Actuator – Q14A Exhaust Gas Recirculation Valve 1 – Q14B Exhaust Gas Recirculation Valve 2 – Q17 Fuel Injector – Q38 Throttle Body – Q61 Reductant Injector Barometric Pressure = Greater than 70 kPa (10.2 PSI) Ambient Air Temperature Sensor Greater than −9°C (16°F) Engine = Running Particulate Filter Regeneration Status = Not required DTC P2C7A runs when the above conditions are met. Conditions for Setting the DTC The selective catalytic reduction catalyst 2 measured NOx conversion efficiency is lower than expected. Action Taken When the DTC Sets DTCs P2C7A is a Type A DTC. Conditions for Clearing the DTC DTCs P2C7A is a Type A DTC. Diagnostic Aids A leak in the reductant system can be located by inspecting for a build-up of crystallized diesel exhaust fluid (Reductant). The reductant injector may temporarily stick after the engine is off for a short period and cause DTC P20EE or P2BAA to set. The reductant injector may unstick after exposure to elevated exhaust temperatures after the engine is restarted. Water in the Reductant tank will cause DTCs to set. Using the Reductant Injector Device Control, a ticking sound should be heard at the reductant injector. Using fuel other than ultra low sulfur content fuel will cause this DTC to set. Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Master Electrical Component List Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References for scan tool information Circuit/System Verification

  1. Verify DTC P202E, P20EE, P2BAA, P30B5, U010E, U029D, U029E, U02A1 is not set. ⇒ If the DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If the DTC is not set
  2. Verify there are no DTCs set related to the following component/system: B9 Ambient Air Temperature Sensor B17 Barometric Pressure Sensor B26 Crankshaft Position Sensor B34 Engine Coolant Temperature Sensor B65 Intake Manifold Pressure and Air Temperature Sensor B75C Multifunction Intake Air Sensor B115 Vehicle Speed Sensor B131 Exhaust Temperature Sensor B154 Diesel Particulate Filter Exhaust Differential Pressure Sensor B195 Nitrogen Oxides Sensor B345R Exhaust Pressure Differential Sensor - Exhaust Gas Recirculation K115 Reductant Control Module M103 Turbocharger Vane Position Actuator M122 Exhaust Pressure Control Valve Actuator Q14A Exhaust Gas Recirculation Valve 1 Q14B Exhaust Gas Recirculation Valve 2 Q17 Fuel Injector Q38 Throttle Body Q61 Reductant Injector ⇒ If a related DTC is set 2.1. Refer to: Diagnostic Trouble Code (DTC) List - Vehicle 2.2. Perform the scan tool Reductant System Malfunction Warning Service Bay Test after diagnosing other DTCs ⇒ If the procedure/test does not pass Refer to: Circuit/System Testing b ⇓ If the procedure/test passes All OK. ⇓ If a related DTC is not set
  3. Verify DTC P2C7A is not set. ⇒ If the DTC is set Refer to: Circuit/System Testing ⇓ If the DTC is not set
  4. All OK. Circuit/System Testing
  5. Ignition OFF. Test the reductant system for contamination. Refer to Contaminants-in-Diesel Exhaust Fluid Diagnosis. ⇒ If any conditions are found Repair as necessary ⇓ If no conditions are found
  6. Ignition ON, command the Reductant System Priming and Leak Test Device Control.
  7. Verify that the reductant pressure sensor parameter is greater than 450 kPa. ⇒ If less than the specified range 3.1. Command the Reductant Pump Duty Cycle Command Device Control to 50% with a scan tool. 3.2. Verify that the desired Reductant Pump Speed and actual Reductant Pump Speed parameters are equal. ⇒ If not equal Refer to DTC P149F, P208A-P208D, P214E, or P2C11 ⇓ If equal ⇓ If within the specified range
  8. Verify there are no leaks, kinks or restrictions in the reductant lines ⇒ If any condition is found Repair as necessary ⇓ If no conditions are found
  9. Verify the 307581 Reductant Fluid Injector Quantity Test passes. ⇒ If the test does not pass Repair as necessary ⇓ If the test passes
  10. Disconnect the Q61 Reductant Injector electrical connector.
  11. Idle engine at 1,500 RPM for 10 min
  12. NOx sensors at operating temperature, idle engine at 700 RPM until Exhaust Gas Temperature Sensor 2 is colder than 150°C (302°F).
  13. Verify the scan tool parameter: Nitrogen Oxides Sensor  3 Nitrogen Oxides Concentration = Not more than 50ppm greater than the following parameter: NOx sensor 1 NOx Concentration. ⇒ If NOx sensor 3 NOx Concentration is 50 ppm or greater than NOx sensor 1 NOx Concentration Replace the B195B Nitrogen Oxides Sensor 3 ⇓ If NOx sensor 3 NOx Concentration is not more than 50 ppm greater than NOx sensor 1 NOx Concentration
  14. Verify NOx sensor  3 NOx Concentration less than 50 ppm greater than NOx sensor 2 NOx Concentration. ⇒ If NOx sensor 3 NOx Concentration is 50 ppm or greater than NOx sensor 2 NOx Concentration Replace the B195B Nitrogen Oxides Sensor 2 ⇓ If NOx sensor 3 NOx Concentration is not more than 50 ppm greater than NOx sensor 2 NOx Concentration
  15. Connect the Q61 Reductant Injector electrical connector.
  16. Verify none of the conditions listed below exist: Exhaust system leaks. Refer to Symptoms - Engine Exhaust Leaking fuel injectors. Refer to Cylinder Power Balance Test. Engine oil consumption. Refer to Oil Consumption Diagnosis. Engine coolant consumption. Refer to Coolant in Combustion Chamber. An engine mechanical condition. Refer to Symptoms - Engine Mechanical. Charge air cooler leaks. Refer to Full System Air Test Charge Air Cooler Diagnosis ⇒ If any condition is found Repair as necessary ⇓ If no condition is found
  17. Replace SCR Catalyst 2. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Nitrogen Oxides Sensor Replacement - Position 1 Nitrogen Oxides Sensor Replacement - Position 2 Nitrogen Oxides Sensor Replacement - Position 3 Nitrogen Oxides Catalytic Converter Replacement — Without Particulate Filter Repair Verification
  1. Perform the scan tool Reductant System Malfunction Service Bay Test ⇒ If the test does not pass Refer to Circuit/System Testing. ⇓ If the test passes
  2. All OK.