Scan Tool Does Not Communicate with Keyword Data Line
Scan Tool Does Not Communicate with Keyword Data Line
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using the diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
Certain modules communicate with a scan tool via the keyword 2000 serial data circuit. The keyword 2000 system is for diagnostics of those modules only. There is no communication between any other modules on the keyword 2000 serial data system.
Diagnostic Aids
* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of-communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
- A control module on the data communication circuit was disconnected while the communication circuit is awake.
- Power to one or more modules was interrupted during diagnosis
- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
* An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
* Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN communications with the scan tool.
* The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment of one or more of the following concerns:
- Vehicle will not crank.
- Vehicle cranks but will not start.
- Vehicle stability enhancement system warning lights and messages.
- PRNDL gear indicator position errors.
- Tire Pressure Monitor (TPM) system warning lights.
Reference Information
Schematic Reference
Data Communication Schematics (with WHB) (Data Communication Schematics (with WHB))Data Communication Schematics (without WHB) (Data Communication Schematics (without WHB))
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Data Link Communications Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Testing
1. Ignition OFF, disconnect the harness connectors of the module that is not communicating with the scan tool.
2. Test for less than 1ohm between the module ground circuit terminal and ground.
• If greater than the specific range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify that a test lamp illuminates between the battery positive voltage circuit terminal and ground.
• If the test lamp does not illuminate, test the battery positive voltage circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test any positive voltage outputs of the module for a short to ground. If all circuits test normal, replace the module.
4. Ignition ON, if applicable, verify that a test lamp illuminates between any ignition voltage circuit terminals and ground.
• If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test any positive voltage outputs of the module for a short to ground. If all circuits test normal, replace the module.
5. Test for infinite resistance between the data link connector (DLC) keyword 2000 serial data circuit terminal and ground.
• If less than the specified value, test the serial data circuit for a short to ground.
6. Test for less than 1V between the DLC keyword 2000 serial data circuit terminal and ground.
• If greater than the specified range, test the serial data circuit for a short to voltage.
7. Test for less than 1ohm in the keyword 2000 serial data circuit between the module connector terminal and the DLC terminal.
• If greater than the specified range, test the serial data circuit for open/high resistance.
8. If all circuits test normal, replace module.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning) for module replacement, setup, and programming