U0170
DTC U0100-U0299
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this 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
The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health (SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn sets a DTC associated with the loss of SOH of the non-communicating control module.
Conditions for Running the DTC
The system voltage is between 9-16 volts.
Conditions for Setting the DTC
A supervised periodic message that includes the transmitter module availability has not been received.
Action Taken When the DTC Sets
Specific subsystems will not function.
Conditions for Clearing the DTC
* A current DTC clears when the malfunction is no longer present.
* A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.
Diagnostic Aids
* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U-code.
* 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.
* Communication may be available between the IPC and the scan tool with either the low or high speed GMLAN serial data system inoperative. This condition is due to the IPC using both the low and high speed GMLAN systems.
* Use Data Link References (Initial Inspection and Diagnostic Overview) to determine if the module uses high or low speed GMLAN serial data communications.
* Some control modules 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 control module.
* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to, providing the vehicle is equipped with the control module.
Reference Information
Schematic Reference
Data Communication Schematics (without WHB) (Data Communication Schematics (without WHB))Data Communication Schematics (with WHB) (Data Communication Schematics (with 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 (Control Module References) for scan tool information
Circuit/System Verification
Verify that following IPC DTCs are not present:
* B1370
* B1380
* B1428
* B1441
• If any listed DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle () to diagnose that DTC prior to this diagnostic.
Circuit/System Testing
Note: Use the schematic to identify the following:
* Control modules the vehicle is equipped with
* Control module locations on the low and high speed GMLAN serial data circuits
* The control modules B+, ignition, ground, communication enable and serial data circuit terminals
1. Determine the module that is not communicating.
2. Ignition OFF, disconnect the necessary harness connector of the module that is not communicating.
3. Test for less than 5 ohm between each ground circuit terminal and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup circuit terminal and ground.
• If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the DLC terminal listed below:
* Low speed GMLAN serial data terminal 1
* High speed GMLAN serial data terminal 6 or 14
• If greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module and a module setting the DTC or a serial data splice pack.
8. If all circuits test normal, replace the control module that is not communicating.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* GMLAN Wiring Repairs (GMLAN Wiring Repairs)
* Control Module References (Control Module References)for module replacement, setup, and programming