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 OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3m (9.8ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down. Disconnect all the harness connectors at the device that is not communicating.
Test for less than 10Ω between each ground circuit terminal and ground.
- If 10Ω or greater
1. Ignition OFF.
2. Test for less than 2Ω in the ground circuit end to end.
  - If 2Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2Ω, repair the open/high resistance in the ground connection.
- If less than 10Ω
Ignition ON.
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 OFF.
2. Test for less than 2Ω in the B+ circuit end to end.
  - If 2Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2Ω, 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 OFF.
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.
- 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 OFF.
2. Test for less than 2Ω in the ignition circuit end to end.
  - If 2Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2Ω, 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 OFF.
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.
- 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 OFF, disconnect the harness connectors at the control module that controls the 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.
  - If infinite resistance
3. Test for less than 2Ω in the ignition circuit end to end.
  - If 2Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2Ω, replace the control module that controls the ignition circuit.
- If the test lamp illuminates
Test for less than 4.5V between each GMLAN serial data circuit terminal and ground.
- If 4.5V 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 4.5V 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 less than 4.5V
Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3m (9.8ft) away from vehicle. It may take up to 2 min for all vehicle systems to power down.
Test for greater than 100Ω between each GMLAN serial data circuit terminal and ground.
- If 100Ω 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 100Ω 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 greater than 100Ω
Test for less than 2Ω in each of the serial data circuits end to end between the device harness connector and the X84 Data Link Connector terminals listed below.
- Low speed GMLAN serial data circuit terminal 1
- High speed GMLAN serial data circuit terminal 6 or 14
- Mid speed GMLAN serial data circuit terminal 3 or 11
- Chassis high speed GMLAN serial data circuit terminal 12 or 13
- Object high speed GMLAN serial data circuit terminal 3 or 11
- If 2Ω or greater
  Repair the open/high resistance in the serial data circuit between the non communicating device and the device setting the DTC or a serial data splice pack.
- If less than 2Ω

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