Skip to content
Tahoe / Yukon Service Manual

Scan Tool Does Not Communicate with Vehicle

Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
K56 Serial Data Gateway Module B+ 1 1 — —
X84 Data Link Connector CAN 6 Serial Data [+] Terminal 6 1 1 1 —
X84 Data Link Connector CAN 6 Serial Data [−] Terminal 14 1 1 1 —
K56 Serial Data Gateway Module Ground — 1 — —
X84 Data Link Connector Ground Terminal 5 — 1 — —
1. No communication with the vehicle.

Circuit/System Description The K56 Serial Data Gateway Module is used to handle communications between multiple CAN buses and functions as a gateway to isolate the secure networks from the unsecured networks. When the K56 Serial Data Gateway Module is not communicating, the scan tool can not communicate with the vehicle. Diagnostic Aids An open in the X84 Data Link Connector ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. Reference Information Schematic Reference Data Communication Schematics Control Module References Connector End View Reference Master Electrical Component List Description and Operation Data Link Communications Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Circuit/System Verification

  1. 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.
  2. Verify a test lamp illuminates between the ground circuit terminal 5 at the X84 Data Link Connector and B+. ⇒ If the test lamp does not illuminate Repair the open/high resistance in the ground circuit or ground connection. ⇓ If the test lamp illuminates
  3. Refer to Circuit/System Testing. Circuit/System Testing
  1. Ignition ON/Vehicle In Service Mode.
  2. Test for less than 4.5 V between each of the CAN 6 serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 6 X84 Data Link Connector terminal 14 ⇒ If 4.5 V or greater 2.1. Ignition/Vehicle OFF, disconnect the harness connectors at the K56 Serial Data Gateway Module. 2.2. Ignition ON/Vehicle In Service Mode. 2.3. Test for less than 1 V between the CAN 6 serial data circuit terminal and ground. ⇒ If 1 V or greater, repair the short to voltage in the serial data circuit. ⇒ If less than 1 V, replace the K56 Serial Data Gateway Module. ⇓ If less than 4.5 V
  3. 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.
  4. Test for greater than 100 Ω between each of the CAN 6 serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 6 X84 Data Link Connector terminal 14 ⇒ If 100 Ω or less 4.1. Disconnect the harness connectors at the K56 Serial Data Gateway Module. 4.2. Test for infinite resistance between the CAN 6 serial data circuit terminal and ground. ⇒ If less than infinite resistance, repair the short to ground in the serial data circuit. ⇒ If infinite resistance, replace the K56 Serial Data Gateway Module. ⇓ If greater than 100 Ω
  5. Test for 110–130 Ω between the CAN 6 serial data circuit terminals 6 and 14 at the X84 Data Link Connector. ⇒ If less than 110 Ω 5.1. Disconnect the harness connectors at the K56 Serial Data Gateway Module. 5.2. Test for infinite resistance between the pair of CAN 6 serial data circuit terminals. ⇒ If less than infinite resistance, repair the short together in the serial data circuits. ⇒ If infinite resistance, replace the K56 Serial Data Gateway Module. ⇒ If greater than 130 Ω 5.1. Disconnect the harness connectors at the K56 Serial Data Gateway Module. 5.2. Test for less than 2 Ω in each of the CAN 6 serial data circuits end to end between the X84 Data Link Connector and the K56 Serial Data Gateway Module. ⇒ If 2 Ω or greater, repair the open/high resistance in the serial data circuit. ⇒ If less than 2 Ω, replace the K56 Serial Data Gateway Module. ⇓ If between 110–130 Ω
  6. Ignition ON/Vehicle In Service Mode.
  1. Test for less than 4.5 V between each of the CAN 7 serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 1 X84 Data Link Connector terminal 9 ⇒ If 4.5 V or greater 7.1. Ignition/Vehicle OFF, disconnect the harness connectors at the K56 Serial Data Gateway Module. 7.2. Ignition ON/Vehicle In Service Mode. 7.3. Test for less than 1 V between the CAN 7 serial data circuit terminal and ground. ⇒ If 1 V or greater, repair the short to voltage in the serial data circuit. ⇒ If less than 1 V, replace the K56 Serial Data Gateway Module. ⇓ If less than 4.5 V
  2. 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.
  3. Test for greater than 100 Ω between each of the CAN 7 serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 1 X84 Data Link Connector terminal 9 ⇒ If 100 Ω or less 9.1. Disconnect the harness connectors at the K56 Serial Data Gateway Module. 9.2. Test for infinite resistance between the CAN 7 serial data circuit terminal and ground. ⇒ If less than infinite resistance, repair the short to ground in the serial data circuit. ⇒ If infinite resistance, replace the K56 Serial Data Gateway Module. ⇓ If greater than 100 Ω
  4. Test for 110–130 Ω between the CAN 7 serial data circuit terminals 1 and 9 at the X84 Data Link Connector. ⇒ If less than 110 Ω 10.1. Disconnect the harness connectors at the K56 Serial Data Gateway Module. 10.2. Test for infinite resistance between the pair of CAN 7 serial data circuit terminals. ⇒ If less than infinite resistance, repair the short together in the serial data circuits. ⇒ If infinite resistance, replace the K56 Serial Data Gateway Module. ⇒ If greater than 130 Ω 10.1. Disconnect the harness connectors at the K56 Serial Data Gateway Module. 10.2. Test for less than 2 Ω in each of the CAN 7 serial data circuits end to end between the X84 Data Link Connector and the K56 Serial Data Gateway Module. ⇒ If 2 Ω or greater, repair the open/high resistance in the serial data circuit. ⇒ If less than 2 Ω, replace the K56 Serial Data Gateway Module. ⇓ If between 110–130 Ω
  5. Disconnect the harness connectors at the K56 Serial Data Gateway Module.
  6. Ignition ON/Vehicle In Service Mode.
  7. Test for less than 1 V between the Ethernet bus 1 enable signal circuit terminal 8 at the X84 Data Link Connector and ground: ⇒ If 1 V or greater Repair the short to voltage in the Ethernet bus 1 enable signal circuit. ⇓ If less than 1 V
  8. 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.
  9. Test for infinite resistance between the Ethernet bus 1 enable signal circuit terminal 8 at the X84 Data Link Connector and ground: ⇒ If less than infinite resistance Repair the short to ground in the Ethernet bus 1 enable signal circuit. ⇓ If infinite resistance
  10. Test for less than 2 Ω in the Ethernet bus 1 enable signal circuit end to end between the X84 Data Link Connector and the K56 Serial Data Gateway Module. ⇒ If 2 Ω or greater Repair the open/high resistance in the Ethernet bus 1 enable signal circuit. ⇓ If less than 2 Ω
  11. Ignition ON/Vehicle In Service Mode.
  12. Test for less than 1 V between each of the Ethernet 1R serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 3 X84 Data Link Connector terminal 11 ⇒ If 1 V or greater Repair the short to voltage in the serial data circuit. ⇓ If less than 1 V
  13. 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.
  14. Test for infinite resistance between each of the Ethernet 1R serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 3 X84 Data Link Connector terminal 11 ⇒ If less than infinite resistance Repair the short to ground in the serial data circuit. ⇓ If infinite resistance
  15. Test for infinite resistance between the Ethernet 1R serial data circuit terminals 3 and 11 at the X84 Data Link Connector. ⇒ If less than infinite resistance Repair the short together in the serial data circuits. ⇓ If infinite resistance
  16. Test for less than 2 Ω in each of the Ethernet 1R serial data circuits end to end between the X84 Data Link Connector and the K56 Serial Data Gateway Module. ⇒ If 2 Ω or greater Repair the open/high resistance in the serial data circuit. ⇓ If less than 2 Ω
  17. Ignition ON/Vehicle In Service Mode.
  18. Test for less than 1 V between each of the Ethernet 1T serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 12 X84 Data Link Connector terminal 13 ⇒ If 1 V or greater Repair the short to voltage in the serial data circuit. ⇓ If less than 1 V
  19. 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.
  20. Test for infinite resistance between each of the Ethernet 1T serial data circuit terminals listed below and ground: X84 Data Link Connector terminal 12 X84 Data Link Connector terminal 13 ⇒ If less than infinite resistance Repair the short to ground in the serial data circuit. ⇓ If infinite resistance
  21. Test for infinite resistance between the Ethernet 1T serial data circuit terminals 12 and 13 at the X84 Data Link Connector. ⇒ If less than infinite resistance Repair the short together in the serial data circuits. ⇓ If infinite resistance
  22. Test for less than 2 Ω in each of the Ethernet 1T serial data circuits end to end between the X84 Data Link Connector and the K56 Serial Data Gateway Module. ⇒ If 2 Ω or greater Repair the open/high resistance in the serial data circuit. ⇓ If less than 2 Ω
  23. Verify a test lamp illuminates between the ground circuit terminal at the K56 Serial Data Gateway Module and B+. ⇒ If the test lamp does not illuminate Repair the open/high resistance in the ground circuit or ground connection. ⇓ If the test lamp illuminates
  24. Ignition ON/Vehicle In Service Mode.
  25. Verify a test lamp illuminates between the B+ circuit terminal at the K56 Serial Data Gateway Module and ground. ⇒ If the test lamp does not illuminate and the circuit fuse is good 31.1. Test for an open/high resistance in the B+ circuit. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 31.2. 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 31.1. Test for a short to ground in the B+ circuit. ⇒ If a short to ground is found, repair the fault in the circuit. ⇓ If a short to ground is not found 31.2. Replace the K56 Serial Data Gateway Module. ⇓ If the test lamp illuminates
  1. Replace the K56 Serial Data Gateway Module.
  2. Ignition ON/Vehicle In Service Mode.
  3. Verify the scan tool is communicating with vehicle. ⇒ If the scan tool is not communicating with vehicle Refer to the scan tool user guide. ⇓ If the scan tool is communicating with vehicle
  4. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification. For control module replacement, programming, and setup, refer to: Control Module References