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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 22 (Engine Controls And Fuel - 2.8L (LWN) Diesel - Diagnostic Information And Procedures (2 Of 3)) >> Diagnostic Information and Procedures >> DTC P157A or P16D7-P16D9 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.

Test 1

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Remove the component : KR121A Reductant Control Module Relay 1 & KR121B Reductant Control Module Relay 2
  3. Ignition - On / Vehicle - In Service Mode
  4. Verify a test lamp turns On between the test points :
    • {KR121A Reductant Control Module Relay 1} B+ circuit terminal 86 & Ground
    • {KR121B Reductant Control Module Relay 2} B+ circuit terminal 85 & Ground
    • If the test lamp does not turn On and the circuit fuse is OK 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for less than 2 ohms between the test points :
      • {KR121A Reductant Control Module Relay 1} B+ circuit terminal 86 @ Relay Socket & Output terminal @ F5UB Fuse
      • {KR121B Reductant Control Module Relay 2} B+ circuit terminal 85 @ Relay Socket & Output terminal @ F5UB Fuse
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Verify the fuse is OK and there is voltage at the fuse.
    • If the test lamp does not turn On and the circuit fuse is open 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for infinite resistance between the test points :
      • {KR121A Reductant Control Module Relay 1} B+ circuit terminal 86 & Ground
      • {KR121B Reductant Control Module Relay 2} B+ circuit terminal 85 & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance - Replace the component : KR121A Reductant Control Module Relay 1 or KR121B Reductant Control Module Relay 2
    • Go to next step : If the test lamp turns On 
  5. Connect a test lamp between the test points :
    • {KR121A Reductant Control Module Relay 1} B+ circuit terminal 86 & Control circuit terminal 85
    • {KR121B Reductant Control Module Relay 2} B+ circuit terminal 85 & Control circuit terminal 86
  6. Perform the scan tool control function : Sensor Supply Voltage Relay - On and Off

    Verify the test lamp turns On and Off.

    • If the test lamp is always Off 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector : X3 @ K20 Engine Control Module
    3. Ignition - On / Vehicle - In Service Mode
    4. Test for less than 1 V between the test points :
      • {KR121A Reductant Control Module Relay 1} Control circuit terminal 85 @ Relay Socket & Ground
      • {KR121B Reductant Control Module Relay 2} Control circuit terminal 86 @ Relay Socket & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • Go to next step : If less than 1 V
    5. Ignition/Vehicle - Off
    6. Test for less than 2 ohms between the test points :
      • {KR121A Reductant Control Module Relay 1} Control circuit terminal 85 @ Relay Socket & The other end of the circuit @ Control module harness
      • {KR121B Reductant Control Module Relay 2} Control circuit terminal 86 @ Relay Socket & The other end of the circuit @ Control module harness
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component : K20 Engine Control Module
    • If the test lamp is always On 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector : X3 @ K20 Engine Control Module
    3. Test for infinite resistance between the test points :
      • {KR121A Reductant Control Module Relay 1} Control circuit terminal 85 @ Relay Socket & Ground
      • {KR121B Reductant Control Module Relay 2} Control circuit terminal 86 @ Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • If infinite resistance - Replace the component : K20 Engine Control Module
    • Go to next step : If the test lamp turns On and Off 
  7. Test or replace the component : KR121A Reductant Control Module Relay 1orKR121B Reductant Control Module Relay 2

Test 2

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Remove the component : KR121B Reductant Control Module Relay 2
  3. Test for less than 1 V between the test points : Control circuit terminal 87 & Ground
    • If 1 V or greater 

      Repair the short to voltage on the circuit :

    • Go to next step : If less than 1 V 
  4. Test or replace the component : KR121B Reductant Control Module Relay 2
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