Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC U2100: Controller Area Network (CAN) Bus CommunicationDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
CAN High | U2104 | U2106/U2108 | U2104 | -- |
CAN Low | U2104 | U2106/U2108 | U2104 | -- |
Circuit/System Description
Modules connected to the CAN serial data circuits monitor communications. During normal vehicle operation, information and commands are exchanged among modules. If the ECM fails to receive an expected message from one of the other modules, DTC U1800, U2106, or U2108 will set; depending on what communication is lost. If no communication is detected on the CAN serial data bus, a DTC U2100 is set. A no communication condition may result from a short to voltage, short to ground, or short between the CAN high and low circuits.
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The module supply voltage is in the normal operating range of 9-16 volts. |
Conditions for Setting the DTC
A no communication condition is detected on CAN serial data circuits.
Action Taken When the DTC Sets
| • | The module uses a default value for the missing parameter. |
| • | The malfunction indicator lamp (MIL) illuminates. |
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, without a repeat of the malfunction. |
Diagnostic Aids
The modules communicating on the CAN serial data circuits are wired parallel to each other until the respective circuits are spliced together outside of the ECM. An open in the CAN circuits for one module will not affect other modules. A short to ground or short to voltage affects all modules no matter where the failure occurs.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool References
Control Module References for Scan Tool Information
Circuit/System Testing
- Ignition OFF, disconnect all module harness connectors and external resistor connectors containing the CAN high and CAN low circuits.
- Ignition ON, verify that a test lamp does not illuminate between the CAN high serial data circuit terminals and ground, and the CAN low serial data circuit terminals and ground of all connectors.
- Ignition ON, verify that a test lamp does not illuminate between the CAN high serial data circuit terminals and B+, and the CAN low serial data circuit terminals and B+ of all connectors.
- Test for infinity between the CAN high serial data circuit terminals and the CAN low serial data circuit terminals at all harness connectors.
- Ignition OFF, remove the CAN high serial data circuit and CAN low serial data circuit terminals listed from the harness connector X1 of the ECM. Reconnect the harness connector X1 of the ECM.
- Reconnect each module, one at a time, and with the engine running measuring for greater than 35,000 Hz (frequency) between the CAN serial data circuit terminals that were removed in the previous step.
- If all circuits test normal, replace ECM.
| ⇒ | If the test lamp illuminates, test the CAN serial data circuit for a short to voltage. |
| ⇒ | If the test lamp illuminates, test the CAN serial data circuit for a short to ground. |
| ⇒ | If less than the specified value, test for a short between the CAN high and low serial data circuits. |
RPO LG4
| • | Terminal 17 |
| • | Terminal 18 |
RPO LG5
| • | Terminal 50 |
| • | Terminal 34 |
Important: After each frequency test, disconnect the connector of the module tested to isolate the next module to be tested. Ensure the ignition is OFF prior to any module connect or disconnect.
| ⇒ | If less than the specified range, replace the module that caused the low reading. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for module replacement, setup and programming
