Circuit/System Verification

Ignition ON/Vehicle In Service Mode.
Verify that the scan tool is communicating with vehicle.
- If the scan tool is not communicating with vehicle
  Refer to Scan Tool Does Not Communicate with Vehicle .
- Go to next step: If the scan tool is communicating with vehicle
Attempt to communicate with all devices on the low speed GMLAN bus. Refer to Data Link References to determine how many devices should be communicating on the low speed GMLAN bus.
Verify two or more devices are not communicating on the low speed GMLAN bus.
- If only one device is not communicating
  Refer to Circuit/System Testing - Testing the Device Circuits.
- Go to next step: If two or more devices are not communicating
Ignition/Vehicle OFF, disconnect the scan tool from the X84 Data Link Connector. The following tests will be done at the X84 Data Link Connector.
Ignition ON/Vehicle In Service Mode.
Test for less than 4.5 V between the serial data circuit terminal 1 and ground.
- If 4.5 V or greater
  Repair the short to voltage in the serial data circuit between the X84 Data Link Connector and the K56 Serial Data Gateway Module.
- 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 the serial data circuit terminal 1 and ground.
- If 100 Ω or less
  Repair the short to ground in the serial data circuit between the X84 Data Link Connector and the K56 Serial Data Gateway Module.
- Go to next step: If greater than 100 Ω
Test for less than infinite resistance between the serial data circuit terminal 1 and ground.
- If infinite resistance
  Repair the open/high resistance in the serial data circuit between the X84 Data Link Connector and the K56 Serial Data Gateway Module.
- Go to next step: If less than infinite resistance
Refer to Circuit/System Testing - Serial Data Starting Point.