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.

NOTE:

Use the schematics and connector end views to identify the device's ground, B+, ignition, and serial data circuit terminals.

Ignition/Vehicle OFF, disconnect the harness connectors at the K20 Engine Control Module.
Verify a test lamp illuminates between each of the ground circuit terminals and B+.
- If the test lamp does not illuminate
  Repair the open/high resistance in the ground circuit or ground connection.
- Go to next step: If the test lamp illuminates
Ignition ON/Vehicle In Service Mode.
If equipped, verify a test lamp illuminates between each of the B+ circuit terminals and ground.
- If the test lamp does not illuminate and the circuit fuse is good
1. Test for an open/high resistance in the B+ circuit.
  - If an open/high resistance is found, repair the fault on the circuit.
  - Go to next step: If an open/high resistance is not found
2. 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
1. Test for a short to ground in the B+ circuit.
  - If a short to ground is found, repair the fault in the circuit.
  - Go to next step: If a short to ground is not found
2. Replace the K20 Engine Control Module.
- Go to next step: If the test lamp illuminates
If equipped, verify a test lamp illuminates between each of the ignition circuit terminals, which has a fuse in the circuit, and ground.
- If the test lamp does not illuminate and the circuit fuse is good
1. Test for an open/high resistance in the ignition circuit.
  - If an open/high resistance is found, repair the fault in the circuit.
  - Go to next step: If an open/high resistance is not found
2. 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
1. Test for a short to ground in the ignition circuit.
  - If a short to ground is found, repair the fault in the circuit.
  - Go to next step: If a short to ground is not found
2. Replace the K20 Engine Control Module.
- Go to next step: If the test lamp illuminates
Test for less than 4.5 V between each of the powertrain CAN serial data circuit terminals and ground.
- If 4.5 V or greater
  Refer to DTC U0076 to test for a short to voltage.
- Go to next step: If less than 4.5 V
Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down.
Test for greater than 100 Ω between each of the powertrain CAN serial data circuit terminals and ground.
- If 100 Ω or less
  Refer to DTC U0076 to test for a short to ground.
- Go to next step: If greater than 100 Ω
Disconnect the harness connectors at the K212 Gear Shift Control Module.
Test for less than 2 Ω in each of the powertrain CAN serial data circuits end to end between the K20 Engine Control Module and the K212 Gear Shift Control Module.
- If 2 Ω or greater
  Repair the open/high resistance in the serial data circuit.
- Go to next step: If less than 2 Ω
Reconnect the harness connectors at the K212 Gear Shift Control Module.
Test for 110 - 130 Ω between each pair of the powertrain CAN serial data circuits at the K20 Engine Control Module.
- If less than 110 Ω
  Refer to DTC U0076 to test for a short between the serial data circuits.
- If greater than 130 Ω
  Refer to DTC U0076 to test for an open/high resistance in the serial data circuit.
- Go to next step: If between 110 - 130 Ω
Replace the K20 Engine Control Module.