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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 92 (Engine Controls And Fuel - 2.8L (LWN) Diesel - Diagnostic Information And Procedures (1 Of 3)) >> Diagnostic Information and Procedures >> DTC P0191-P0194, P127C, or P127D >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
    NOTE:

    It may take up to 2 min for all vehicle systems to power down before an accurate ground or low reference circuit continuity test can be performed.

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Disconnect the electrical connector: B47B Fuel Rail Pressure Sensor
  3. Test for less than 10 ohms between the test points: Low Reference circuit terminal 1 & Ground
    • If 10 ohms or greater 
    1. Disconnect the appropriate electrical connector: @ K20 Engine Control Module
    2. Test for less than 2 ohms between the test points: Low Reference circuit terminal 1 @ Component harness & Terminal 69 @ 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
    • Go to next step: If less than 10 ohms 
  4. Ignition - On / Vehicle - In Service Mode
  5. Test for 4. 8 to 5. 2 V between the test points: 5 V Reference circuit terminal 3 & Low Reference circuit terminal 1
    • If less than 4. 8 V 
    1. Ignition/Vehicle - Off
    2. Disconnect the appropriate electrical connector: @ K20 Engine Control Module
    3. Test for infinite resistance between the test points: 5 V Reference circuit terminal 3 @ Component harness & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    4. Test for less than 2 ohms between the test points: 5 V Reference circuit terminal 1 @ Component harness & Terminal 89 @ 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 greater than 5. 2 V 
    1. Ignition/Vehicle - Off
    2. Disconnect the appropriate electrical connector: @ K20 Engine Control Module
    3. Ignition - On / Vehicle - In Service Mode
    4. Test for less than 1 V between the test points: 5 V Reference circuit terminal 3 @ Component harness & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • If less than 1 V - Replace the component: K20 Engine Control Module
    • Go to next step: If between 4. 8 and 5. 2 V 
  6. Verify the scan tool parameter: Fuel Rail Pressure Sensor 1 & Fuel Rail Pressure Sensor 2 = Greater than 4. 8 V
    • If 4. 8 V or less 
    1. Ignition/Vehicle - Off
    2. Disconnect the appropriate electrical connector: @ K20 Engine Control Module
    3. Test for infinite resistance between the test points:
      • Signal circuit terminal 4 @ Component harness & Ground
      • Signal circuit terminal 2 @ Component harness & 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 greater than 4. 8 V 
  7. Connect a 3 A fused jumper wire between the test points:
    • Signal circuit terminal 4 & Ground
    • Signal circuit terminal 2 & Ground
  8. Verify the scan tool parameter: Fuel Rail Pressure Sensor 1 & Fuel Rail Pressure Sensor 2 = Less than 0. 4 V
    • If 0. 4 V or greater 
    1. Ignition/Vehicle - Off & Remove - Jumper wire(s)
    2. Disconnect the appropriate electrical connector: @ K20 Engine Control Module
    3. Ignition - On / Vehicle - In Service Mode
    4. Test for less than 1 V between the test points:
      • Signal circuit terminal 4 @ Component harness & Ground
      • Signal circuit terminal 2 @ Component harness & 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:
      • Signal circuit terminal 4 @ Component harness & Terminal 88 @ Control module harness
      • Signal circuit terminal 2 @ Component harness & Terminal 38 @ 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
    • Go to next step: If less than 0. 4 V 
  9. Test or replace the component: B47B Fuel Rail Pressure Sensor
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