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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 122 (Engine Controls And Fuel - 2.7L (L3B) - Diagnostic Information And Procedures (3 Of 3)) >> Diagnostic Information and Procedures >> DTC P2AB8, P2AB9, P2B81, P2B93, P2C9B, or U0644 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.

Test 1

    NOTE:
    • Disconnecting the component electrical connector causes additional DTCs to set.
    • 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: M128 Turbocharger Wastegate Actuator
  3. Test for less than 5 ohms between the test points: Low Reference circuit terminal 1 & Ground
    • If 5 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 & 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
    • Go to next step: If less than 5 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 3 @ Component harness & 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 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. Test for 3.75 to 4.25 V between the test points: Serial Data circuit terminal 2 @ Component harness & Ground
    • If less than 3.75 V 
    1. Ignition/Vehicle - Off
    2. Disconnect the appropriate electrical connector: K20 Engine Control Module
    3. Test for infinite resistance between the test points: Serial Data circuit terminal 2 @ 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: Serial Data circuit terminal 2 @ Component harness & 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 greater than 4.25 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: Serial Data circuit terminal 2 @ 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 3.75 and 4.25 V 
  7. Test or replace the component: M128 Turbocharger Wastegate Actuator

Test 2

  1. Ignition - On / Vehicle - In Service Mode
  2. Perform the following learn procedure: Turbocharger Wastegate Learn
  3. Ignition/Vehicle & All vehicle systems - Off - For 2 min
  4. Ignition - On / Vehicle - In Service Mode
  5. Operate the vehicle within the Conditions for Running the DTC.

    Verify the DTC does not set.

    • If the DTC sets 
    1. Ignition/Vehicle - Off
    2. Verify a condition does not exist with the component:
    • Linkage @ M128 Turbocharger Wastegate Actuator - Binding or Sticking/Worn/Debris/Dirt/Interference with other components or objects /Modified/Visible Damage
    • Valve @ Turbocharger - Binding or Sticking/Worn/Debris/Dirt/Modified/Visible Damage - Refer to: Compressor Air Intake Turbocharger Overhaul
      • If a condition exists - Repair or replace as necessary & Repeat the procedure starting at step 1 - Test 2
      • If no condition exists - Replace the component: M128 Turbocharger Wastegate Actuator
    • Go to next step: If the DTC does not set 
  6. All OK.
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