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Tahoe / Yukon Service Manual

Scan Tool Does Not Communicate with Device on CAN 8

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
CAN 8 Serial Data [+] (circuit 4105) U007E* U0100– U02FF, U1100– U12FF, U1600– U17FF, U2200– U23FF, U2400– U25FF* U007E* —
CAN 8 Serial Data [−] (circuit 4104) U007E* U0100– U02FF, U1100– U12FF, U1600– U17FF, U2200– U23FF, U2400– U25FF* U007E* —
* Other DTCs may set with this fault.

Circuit/System Description The devices connected to the CAN 8 serial data circuits (4104 & 4105) monitor for serial data communications during normal vehicle operation. The serial data is transmitted on two twisted wires that allow speeds up to 2 Mbit/s. The twisted pair is terminated with two 120 Ω resistors. Each terminating resistor can be a separate resistor in a connector assembly or internal to a device. The resistors are used as the load for the CAN 8 bus during normal vehicle operation. The CAN 8 bus is a differential bus. The CAN 8 serial data [+] and CAN 8 serial data [−] circuits are driven to opposite extremes from a rest or idle level of approximately 2.5 V. Driving the lines to their extremes, adds 1 V to the CAN 8 serial data [+] circuit and subtracts 1 V from the CAN 8 serial data [−] circuit. If serial data is lost, devices will set a no communication code against the non-communicating device. Note that a loss of serial data DTC does not represent a failure of the device that set it. Diagnostic Aids A device may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U code. Do not replace a device reporting a U code. The U code identifies which device needs to be diagnosed for a communication issue. Communication may be available between some devices and the scan tool with the CAN 1 serial data system inoperative. This condition is due to those devices using multiple serial data communication systems. Some devices may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the device. 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 ON/Vehicle In Service Mode.
  2. 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. ⇓ If the scan tool is communicating with vehicle
  3. Ignition/Vehicle OFF, access the Network Communication Status application in scan tool under Vehicle Diagnostics > Vehicle Communication Diagnostics > Network Communication Status.
  4. Verify one or more CAN devices are not communicating. Refer to Network Communication Status to determine the CAN devices that are not communicating. ⇒ If only one device is not communicating Refer to Circuit/System Testing – Testing the Device Circuits. The possible fault can be device’s ground, power, or an open in the CAN serial data circuit between that non communicating device and the K56 Serial Data Gateway Module. ⇒ If two or more devices are not communicating, but not all Refer to Circuit/System Testing — Testing the Device Circuits. The possible fault can be an open in the CAN serial data circuit at the non communicating device closet to the K56 Serial Data Gateway Module. Use the schematic for CAN bus being tested to determine the non communicating device closest to the K56 Serial Data Gateway Module. ⇒ If all devices are not communicating Refer to Circuit/System Testing – Serial Data Starting Point. One of the following faults can occur: A short to voltage in a CAN serial data circuit. A short to ground in a CAN serial data circuit. A short together between CAN serial data circuits. An open/high resistance in a CAN serial data circuit between the K56 Serial Data Gateway Module and the closet non communicating device if the K56 Serial Data Gateway Module is at one end of the bus. Use the schematic for CAN bus being tested to determine the non communicating device closest to the K56 Serial Data Gateway Module. ⇓ If all CAN devices are communicating
  5. A fault is currently not present and may be an intermittent condition. Verifying the communication status using Digital Multimeter
  6. Ignition ON/Vehicle In Service Mode.
  7. 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. ⇓ If the scan tool is communicating with vehicle
  8. Attempt to communicate with all devices on the CAN 8 bus. Refer to Data Link References and Data Communication Schematics to determine how many devices should be communicating on the CAN 8 bus.
  9. Verify two or more devices are not communicating on the CAN 8 bus. ⇒ If only one device is not communicating Refer to Circuit/System Testing – Testing the Device Circuits. ⇓ If two or more devices are not communicating
  10. Refer to Circuit/System Testing – Serial Data Starting Point. Circuit/System Testing
  1. Ignition/Vehicle OFF, disconnect the harness connectors with the CAN 8 serial data circuits at an easily accessible device that is not communicating.
  2. Ignition ON/Vehicle In Service Mode.
  3. Test for less than 4.5 V between each of the CAN 8 serial data circuit terminals at the device that was just disconnected and ground. ⇒ If 4.5 V or greater Refer to Testing the Serial Data Circuits for a Short to Voltage. ⇓ If less than 4.5 V
  4. 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.
  5. Test for greater than 100 Ω between each of the CAN 8 serial data circuit terminals at the device that was just disconnected and ground. ⇒ If 100 Ω or less Refer to Testing the Serial Data Circuits for a Short to Ground. ⇓ If greater than 100 Ω
  6. Test for 110–130 Ω between each pair of the CAN 8 serial data circuit terminals at the device that was just disconnected. ⇒ If less than 110 Ω Refer to Testing the Serial Data Circuits for a Short between the Circuits. ⇒ If greater than 130 Ω Refer to Testing the Serial Data Circuits for an Open/High Resistance. ⇓ If between 110–130 Ω
  7. Replace the device that was just disconnected. Testing the Serial Data Circuits for a Short to Voltage
  8. Ignition/Vehicle OFF, disconnect the harness connectors with the CAN 8 serial data circuits at another device, in the direction of the circuit shorted to voltage.
  9. Ignition ON/Vehicle In Service Mode
  10. Test for greater than 4.5 V between each of the CAN 8 serial data circuits at the device connector that was just disconnected and ground. ⇒ If each serial data circuit is 4.5 V or less Replace the device that was just disconnected. ⇓ If any serial data circuit is greater than 4.5 V
  11. Repeat step 1 until one of the following conditions are isolated: A short to voltage on the serial data circuit between two devices or splice packs, if equipped. A short to voltage on the serial data circuit between a device and a terminating resistor. Testing the Serial Data Circuits for a Short to Ground
  12. 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.
  13. Disconnect the harness connectors with the CAN 8 serial data circuits at another device, in the direction of the circuit shorted to ground.
  14. Test for greater than 100 Ω between each of the CAN 8 serial data circuits at the device connector that was just disconnected and ground. ⇒ If each serial data circuit is 100 Ω or greater Replace the device that was just disconnected. ⇓ If any serial data circuit is less than 100 Ω
  15. Repeat step 1 until one of the following conditions are isolated: A short to ground on the serial data circuit between two devices or splice packs, if equipped. A short to ground on the serial data circuit between a device and a terminating resistor. Testing the Serial Data Circuits for a Short between the Circuits
  16. 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.
  17. Connect the harness connectors at the device that was previously disconnected.
  18. Disconnect the harness connectors with the CAN 8 serial data circuits at another device, in the direction of the circuit shorted together.
  19. Test for greater than 110 Ω between each pair of the CAN 8 serial data circuits at the device connector that was just disconnected. ⇒ If each pair of serial data circuits is 110 Ω or greater Replace the device that was just disconnected. ⇓ If any pair of serial data circuits is less than 110 Ω
  20. Repeat step 1 until one of the following conditions are isolated: Serial data circuits shorted together between two devices or splice packs, if equipped. Serial data circuits shorted together between a device and a terminating resistor. A shorted terminating resistor. Testing the Serial Data Circuits for an Open/High Resistance
  21. 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.
  22. Connect the harness connectors at the device that was previously disconnected.
  23. Disconnect the harness connectors with the CAN 8 serial data circuits at another device, in the direction of the circuit with the open/high resistance.
  24. Test for less than 130 Ω between each pair of the CAN 8 serial data circuits at the device connector that was just disconnected. ⇒ If each pair of serial data circuits is 130 Ω or less Replace the device that was just disconnected. ⇓ If any pair of serial data circuits is greater than 130 Ω
  25. Repeat step 1 until one of the following conditions are isolated: An open/high resistance on the serial data circuit between two devices or splice packs, if equipped. An open/high resistance on the serial data circuit between a device and a terminating resistor. An open/high resistance terminating resistor. Testing the Device Circuits
  26. Ignition/Vehicle OFF, disconnect the harness connectors at the CAN 8 device that is not communicating.
  27. 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. ⇓ If the test lamp illuminates
  28. Ignition ON/Vehicle In Service Mode.
  29. 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 4.1. Test for an open/high resistance in the B+ circuit. ⇒ If an open/high resistance is found, repair the fault in the circuit. ⇓ If an open/high resistance is not found 4.2. 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 4.1. 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 4.2. Replace the disconnected device. ⇓ If the test lamp illuminates
  30. 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 5.1. Test for an open/high resistance in the ignition circuit. ⇒ If an open/high resistance is found, repair the fault in the circuit. ⇓ If an open/high resistance is not found 5.2. 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 5.1. Test for a short to ground in the ignition circuit. ⇒ If a short to ground is found, repair the fault in the circuit. ⇓ If a short to ground is not found 5.2. Replace the disconnected device. ⇓ If the test lamp illuminates
  31. Test for less than 4.5 V between each of the CAN 8 serial data circuit terminals and ground. ⇒ If 4.5 V or greater Refer to Testing the Serial Data Circuits for a Short to Voltage. ⇓ If less than 4.5 V
  32. 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.
  33. Test for greater than 100 Ω between each of the CAN 8 serial data circuit terminals and ground. ⇒ If 100 Ω or less Refer to Testing the Serial Data Circuits for a Short to Ground. ⇓ If greater than 100 Ω
  34. Test for greater than 35 Ω between each pair of the CAN 8 serial data circuit terminals. ⇒ If 35 Ω or less Refer to Testing the Serial Data Circuits for a Short between the Circuits. ⇓ If greater than 35 Ω
  35. Test for less than infinite resistance between each of the CAN 8 serial data circuit terminals and ground. ⇒ If infinite resistance Repair the open/high resistance in the serial data circuit. ⇓ If less than infinite resistance
  36. Inspect both harness and component connectors for contamination, corrosion, and terminal tension.
  37. Reconnect the harness connectors at the CAN 8 device.
  38. Ignition ON/Vehicle In Service Mode.
  39. Verify the CAN 8 device is communicating. ⇒ If the CAN 8 device is not communicating Replace the non communicating device. ⇓ If the CAN 8 device is communicating
  40. A fault is currently not present and may be an intermittent condition. 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