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 Descriptors
DTC U1016: Lost Communications With Engine Control SystemDTC U1024: Lost Communications With Transmission Control System
DTC U1031: Lost Communications With Serial Data Gateway
DTC U1040: Lost Communications With Electronic Brake Control Module (EBCM)
DTC U1064: Lost Communications With Body Multiple Control (BCM) System
DTC U1088: Lost Communications With Restraints Control System
DTC U1096: Lost Communications With Driver Information & Displays Control (IPC) System
DTC U1111: Lost Communications With Chime
DTC U1128: Lost Communications With Radio
DTC U1176: Loss of RFA Communications
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Class 2 Serial Data | 1 | U1001-U1254 | 1 | -- |
Battery Positive Voltage Circuits | -- | U1001-U1254 | -- | -- |
Ignition Voltage Circuits | -- | U1001-U1254 | -- | -- |
Module Ground Circuits | -- | U1001-U1254 | U1001-U1254 | -- |
1. Scan Tool Does Not Communicate with Class 2 Device | ||||
Circuit Description
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring (Node Alive messages). A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that modules "Node Alive" message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a "Node Alive" message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx is set.
A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a Lost Communication DTC set by other modules. The modules that can communicate will set a DTC indicating the module that cannot communicate. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx, where xxx is equal to the 3-digit identification number, is set.
Conditions for Running the DTC
| • | Voltage supplied to the module is in the normal operating voltage range of 9-16 volts. |
| • | Diagnostic trouble codes U1300, U1301 and U1305 do not have a current status. |
| • | The vehicle power mode, ignition switch position, requires serial data communication to occur. |
Conditions for Setting the DTC
A message from a learned identification number has not been detected for the past 5 seconds.
Action Taken When the DTC Sets
The module(s) is never signaled, therefore the specific subsystem(s) 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
| • | Use the DTC Descriptor list above to determine the module which is not communicating. |
| • | Some modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no module output voltage circuit is shorted to ground before replacing the module. |
| • | This diagnostic can be used for any module that should communicate with Class 2 serial data providing the vehicle is equipped with the option that uses that module. |
Reference Information
Schematic Reference
Connector End View Reference
Data Communication Connector End Views
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Circuit/System Testing
- Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
- Ignition OFF, disconnect the harness connector at the module that is not communicating.
- Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
- Verify that a test lamp illuminates between all ignition voltage circuits and ground.
- Test for less than 5 ohms between the module ground circuits and ground.
- Test for less than 1 ohm on the serial data circuit(s) between the non-communicating module and the module that displays the DTC.
- If all circuits test normal, replace the module that is not communicating.
Important: If DTC U1000 or U1255is set as current in any module and there is a U1001-U1254 DTC set in history consider the U1001-U1254 DTC as a current DTC.
| ⇒ | If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the non-communicating module. |
| ⇒ | If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the non-communicating module. |
| ⇒ | If greater than the specified range, test the ground circuit for an open. |
| ⇒ | If greater than the specified range, test the serial data circuit for open/high resistance. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for module replacement, setup, and programming
