Circuit/System Testing

NOTE:

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

Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect all the harness connectors at the device that is not communicating. It may take up to 10 min for all vehicle systems to power down.
Test for less than 10 Ω between each ground circuit terminal and ground.
- If 10 Ω or greater
1. Ignition/Vehicle OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, repair the open/high resistance in the ground connection.
- Go to next step: If less than 10 Ω
Ignition ON/Vehicle In Service Mode.
If equipped, verify a test lamp illuminates between each B+ circuit terminal and ground.
- If the test lamp does not illuminate and the circuit fuse is good
1. Ignition/Vehicle OFF, remove the test lamp.
2. Test for less than 2 Ω in the B+ circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, 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. Ignition/Vehicle OFF, remove the test lamp.
2. Test for infinite resistance between the B+ circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - If infinite resistance, replace the disconnected device.
- Go to next step: If the test lamp illuminates
If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.
- If the test lamp does not illuminate and the circuit fuse is good
1. Ignition/Vehicle OFF, remove the test lamp.
2. Test for less than 2 Ω in the ignition circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
1. Ignition/Vehicle OFF, remove the test lamp.
2. Test for infinite resistance between the ignition circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - If infinite resistance, replace the disconnected device.
- Go to next step: If the test lamp illuminates
If equipped, verify a test lamp illuminates between each ignition circuit terminal, which is controlled by a control module, and ground.
- If the test lamp does not illuminate
1. Ignition/Vehicle OFF, remove the test lamp, disconnect the harness connectors at the control module that controls the ignition circuit and all devices that share the same ignition circuit.
2. Test for infinite resistance between the ignition circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - Go to next step: If infinite resistance
3. Test for less than 2 Ω in the ignition circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - Go to next step: If less than 2 Ω
4. Reconnect the control module that controls the ignition circuit, ignition ON/Vehicle In Service Mode.
5. Verify a test lamp illuminates between the ignition circuit terminal and ground.
  - If the test lamp does not illuminate, replace the control module that controls the ignition circuit.
  - Go to next step: If the test lamp illuminates
6. Ignition/Vehicle OFF, reconnect the first device that shares the same ignition circuit, ignition ON/Vehicle In Service Mode.
7. Verify a test lamp illuminates between the ignition circuit terminal and ground.
  - If the test lamp does not illuminate, replace the device that was just connected.
  - If the test lamp illuminates and there are more devices to connect, connect the next device and repeat step 6.7 until there are no more devices to connect.
- Go to next step: If the test lamp illuminates
If equipped, verify a test lamp illuminates between the accessory wakeup serial data circuit terminal or the serial data communication enable circuit terminal and ground.
- If the test lamp does not illuminate
1. Ignition/Vehicle OFF, remove the test lamp, disconnect the harness connectors at the K9 Body Control Module.
2. Test for less than 2 Ω in the accessory wakeup serial data circuit or the serial data communication enable circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, replace the K9 Body Control Module.
- Go to next step: If the test lamp illuminates
Test for less than 4.5 V between each GMLAN serial data circuit terminal and ground.
- If 4.5 V or greater between a low speed GMLAN serial data circuit and ground
  Refer to Scan Tool Does Not Communicate with Low Speed GMLAN Device to test for a short to voltage.
- If 4.5 V or greater between a high speed GMLAN serial data circuit and ground
  Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device to test for a short to voltage.
- If 4.5 V or greater between a chassis high speed GMLAN serial data circuit and ground
  Refer to Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device 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 GMLAN serial data circuit terminal and ground.
- If 100 Ω or less between a low speed GMLAN serial data circuit and ground
  Refer to Scan Tool Does Not Communicate with Low Speed GMLAN Device to test for a short to ground.
- If 100 Ω or less between a high speed GMLAN serial data circuit and ground
  Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device to test for a short to ground.
- If 100 Ω or less between a chassis high speed GMLAN serial data circuit and ground
  Refer to Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device to test for a short to ground.
- Go to next step: If greater than 100 Ω
Disconnect the harness connectors at the K56 Serial Data Gateway Module.
Test for less than 2 Ω in each of the GMLAN serial data circuits end to end between the non communicating device and the K56 Serial Data Gateway 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 K56 Serial Data Gateway Module.

NOTE:

The following test step is only applicable to a high speed GMLAN device with 2 pairs of serial data circuits or a high speed GMLAN device with an internal terminating resistor.

Test for 110 - 130 Ω between each pair of high speed GMLAN serial data circuits.
- If less than 110 Ω
  Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device to test for a short to ground or a short between the serial data circuits.
- If greater than 130 Ω
  Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device to test for an open/high resistance in the serial data circuit.
- Go to next step: If between 110 - 130 Ω
Replace the device that is not communicating.