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 U2108: Lost Communications With ABS/TCS Control SystemDiagnostic 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
The engine control module (ECM), the electronic brake control module (EBCM), and the transmission control module (TCM) communicate control and diagnostic information via a controller area network (CAN) communication bus. The ECM monitors CAN operational status by expecting a constant flow of messages from the EBCM and the TCM. If the ECM fails to receive an expected message from one of the other modules, DTC U2104, U2106, or U2108 will set, depending on what communication is lost.vv
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
The CAN message from the EBCM is not received by the ECM for 200 milliseconds.
Action Taken When the DTC Sets
The control module will not illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
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 that communicate on the CAN system are wired parallel to each other until the respective circuits are spliced together for the ECM. An open in the CAN circuits of one module will not affect the other module. 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
System Verification
Verify that DTC U2104 is not set.
| ⇒ | If DTC U2104 is set, diagnose that DTC first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle . |
Circuit/System Testing
- Ignition OFF, disconnect the harness connector X1 of the ECM and the EBCM.
- Test for less than 2 ohms on the CAN serial data circuit terminals listed between the ECM and EBCM as follows:
- Test for greater than 50 ohms between harness connector X1 terminal 18 and terminal 17 of the ECM.
- Ignition ON, verify that a test lamp does not illuminate between ground and ECM harness connector X1 terminals as follows.
- Ignition ON, verify that a test lamp does not illuminate between B+ and ECM harness connector X1 terminals as follows.
- If all circuits test normal, replace EBCM.
| • | ECM 18 and EBCM 2 |
| • | ECM 17 and EBCM 6 |
| ⇒ | If greater than the specified range, test the CAN serial data circuit for open/high resistance. |
| ⇒ | If less than the specified range, test for a short between the CAN high and low serial data circuits. |
| • | ECM 18 |
| • | ECM 17 |
| ⇒ | If the test lamp illuminates, test the CAN serial data circuit for a short to voltage. |
| • | ECM 18 |
| • | ECM 17 |
| ⇒ | If the test lamp illuminates, test the CAN serial data circuit for a short to ground. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for module replacement, setup and programming
