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Tahoe / Yukon Service Manual

DTC P220A, P220B, or P23B6

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5507732 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 P220A Nitrogen Oxides Sensor Supply Voltage Circuit DTC P220B Nitrogen Oxides Sensor 2 Supply Voltage Circuit DTC P23B6 Nitrogen Oxides Sensor 3 Supply Voltage Circuit Circuit/System Description The Nox sensors are part of the selective catalytic reduction system, a device used to reduce Nox emission on diesel engines. There are two Nox sensors, one placed upstream of selective catalytic reduction, to measure inlet Nox concentration, and one placed downstream. They are connected with the control module via CAN and all the information is exchanged through it. Since it is a smart sensor, all the electrical monitoring is performed inside the sensor and only the results are sent to the ECM. Each NOx sensor contains a sensing cell, a pumping cell, and a heater. A sample of exhaust gas passes through a diffusion gap between the sensing cell and the pumping cell. The NOx sensor maintains a constant reference voltage across the sensing cell. An electronic circuit within sensor controls the pump current through the pumping cell in order to maintain a constant voltage in the sensing cell. The amount of current required to maintain the reference voltage in the sensing cell is proportional to the concentration of NOx in the exhaust. The ECM varies the amount of diesel exhaust fluid (reductant) added by varying the reductant injector duty cycle in response to changes in engine exhaust NOx levels. The smart NOx sensors consist of two components, the NOx module and the NOx sensor element that are serviced as a unit. A circuit or performance condition with a NOx sensor is detected by the NOx sensor module. The smart NOx sensor module communicates the condition to the ECM over the serial data line. The ECM sets a DTC when a serial data message is received from the NOx sensor module. Conditions for Running the DTC DTC U029D, U029E, or U02A1 is not set The reductant control module relay is ON for greater than 1 s. Ignition and Start Switch Signal = Greater than 11 V Nitrogen Oxides Sensor Heater = Allowed Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC The sensor supply voltage is less than 10.8 V. Action Taken When the DTC Sets DTCs P220A, P220B, and P23B6 are Type B DTCs. Conditions for Clearing the DTC DTCs P220A, P220B, and P23B6 are Type B DTCs. 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. Ignition ON, verify that no other DTCs are set. ⇒ If any other DTCs are set Refer to Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If no other DTCs are set
  2. Verify that DTC P220A, P220B, or P23B6 is not set ⇒ If the DTC is set Refer to Circuit/System Testing ⇓ If the DTC is not set
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
  4. Verify the DTC does not set. ⇒ If the DTC sets Refer to Circuit/System Testing ⇓ If the DTC does not set
  5. All OK. Circuit/System Testing
  6. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at appropriate the B195 Nitrogen Oxides Sensor.
  7. Ignition ON, verify that a test lamp illuminates between the voltage circuit terminal 1 and ground. ⇒ If the test lamp does not illuminate and the circuit fuse is good 2.1. Ignition OFF. 2.2. Test for less than 2 Ω in the voltage circuit end to end. ⇒ If 2 Ω or greater, repair the open/high resistance in the circuit. ⇒ If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse. ⇒ If the test lamp does not illuminate and the circuit fuse is open 2.1. Ignition OFF. 2.2. Test for infinite resistance between the voltage circuit and ground. ⇒ If less than infinite resistance, repair the short to ground on the circuit. ⇒ If infinite resistance, replace the appropriate B195 Nitrogen Oxides Sensor. ⇓ If the test lamp illuminates
  8. Replace the appropriate B195 Nitrogen Oxides Sensor. 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