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
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for Scan Tool Information
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
