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Home >> Cadillac >> 2021 >> CT4 Sport, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 117 (Manual Transmission - TREMEC 6-Speed (Mg9) - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> DTC P0502 or P0503 >> 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.
  1. Ignition/Vehicle & All vehicle systems - Off
  2. Remove the component: B115 Vehicle Speed Sensor
  3. Verify the following conditions do not exist:
    • B115 Vehicle Speed Sensor - Cracked/Debris/Loose
      • NOTE:

      Use a suitable tool to manually move the reluctor ring and ensure that it is not loose.

    • Reluctor Ring - Cracked/Debris/Loose
    • If a condition exists 

      Repair or replace as necessary

    • Go to next step: If no conditions exist 
  4. Disconnect the electrical connector: B115 Vehicle Speed Sensor
    5. 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.

  5. Test for less than 10 ohms between the test points: Low Reference circuit terminal 3/C & 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 3/C @ 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 10 ohms 
  6. Ignition - On / Vehicle - In Service Mode
  7. Test for 4.8 to 5.2 V between the test points: 5 V Reference circuit terminal 1/A & Low Reference circuit terminal 3/C
    • 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 1/A @ 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/A @ 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 1/A @ 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 
  8. Test for greater than 10 V between the test points: Signal circuit terminal 2/B & Ground
    • If 10 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 2/B @ 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 5 ohms between the test points: Signal circuit terminal 2/B @ Component harness & The other end of the circuit @ Control module harness
      • If 5 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 5 ohms - Replace the component: K20 Engine Control Module
    • Go to next step: If greater than 10 V 
  9. Connect a 3 A fused jumper wire between the test points: Signal circuit terminal 2/B & Ground

    Verify the fuse does not open.

    • If the fuse opens 

      Repair the short to voltage on the circuit.

    • Go to next step: If the fuse does not open 
  10. Install & Setup - EL-38522-A  Variable Signal Generator
    • Voltage - 12 V
    • Frequency - 250 Hz
    • Duty Cycle - 50%
    • Red lead @ Signal circuit terminal 2/B
    • Black lead @ Battery Negative Post
  11. Verify the scan tool parameter: Output Shaft Speed Sensor = 840 to 920 RPM
    • If not the specified value 

      Replace the component: K20 Engine Control Module

    • Go to next step: If the specified value 
  12. Test or replace the component: B115 Vehicle Speed Sensor
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