For 1990-2009 cars

Table 1: | The Control Module ID

### 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 2-5 seconds. 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.

The control module ID number list below provides a method for determining which module is not communicating. A module with a class 2 serial data circuit malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that can not communicate. As long as U1300, U1301, and U1305 are not set as current, DTC U1001-U1254 will set.

#### The Control Module ID

Control Module | ID Number
--- | ---
Powertrain Control Module (PCM) (L61) | 016
Body Control Module (BCM) | 064
Sensing and Diagnostic Module (SDM) | 088
Instrument Panel Cluster (IPC) | 096
Vehicle Communication Module (VCIM) | 151
HVAC Control Module | 153

When more than one Loss of Communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order:

1. Current DTCs before history DTCs unless told otherwise in the diagnostic table
2. The DTC which is reported the most times
3. From the lowest number DTC to the highest number DTC

### Conditions for Running the DTC

• | The vehicle power mode, ignition switch position, requires serial data communication to occur.

• | The module supply voltage is in the normal operating range of 9-16 volts.

### Conditions for Setting the DTC

A message from a learned identification number has not been detected for the past 5 seconds.

### Conditions for Clearing the DTC

• | A current DTC will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

### Diagnostic Aids

• | An intermittent open of the class 2 serial data circuit to the inoperative module may cause this code to set.

• | A poor connection at the inoperative module may cause this code to set.

• | An intermittent open in the splice may cause this code to set.

• | An improperly powered module may cause this code to set.

• | A current DTC will clear when a Node Alive, State of Health, message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.

• | A history DTC will clear after 100 engine running cycles with no recurrence of the malfunction.

### Test Description

The number below refers to the step number on the diagnostic table.

1. The module which was not communicating on the class 2 serial data circuit may have set the Loss of Communication DTCs for the modules it was monitoring.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems
1 | Did you perform the Diagnostic System Check for the system exhibiting symptom? | Go to Step 2 | Go to Control Module References in Body Control System for the applicable Diagnostic System Check
2 | Important: Use the control module ID number list in order to determine which module is not communicating. Test the following circuits of the module that is not communicating for an open or a short to ground:

• | The battery positive voltage input circuits

• | The battery positive voltage output circuits

• | The ignition voltage input circuits

• | The ignition voltage output circuits

• | The switched battery positive voltage circuits

Refer to the following:

• | Control Module References in Body Control System

• | Circuit Testing in Wiring Systems

• | Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 3

3 |

1. Turn the ignition OFF.
2. Test the ground circuits of the module that is not communicating for an open.

Refer to the following:

• | Control Module References in Body Control System

• | Circuit Testing in Wiring Systems

• | Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4 | Test the class 2 serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 7 | Go to Step 5
5 | Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits:

• | The battery positive voltage input circuits

• | The battery positive voltage output circuits

• | The ignition voltage input circuits

• | The ignition voltage output circuits

• | The switched battery positive voltage supply circuits

• | The ground circuits

• | The class 2 serial data circuits

Refer to the following:

• | Control Module References in Body Control System

• | Testing for Intermittent Conditions and Poor Connections in Wiring Systems

• | Connector Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6 | Important: Perform the programming or setup procedure for the replaced control module if required. Replace the module that is not communicating. Refer to Control Module References in Body Control System for the applicable replacement procedure. Did you complete the replacement? | Go to Step 7 | --
7 |

1. Install a scan tool.
2. Turn the ignition ON, with the engine OFF.
3. Select the Display DTCs function for the module which was not communicating.

Does the scan tool display any DTCs which do not begin with a "U"?

Go to Control Module References in Body Control System

Go to Step 8

8 | Select the Display DTCs function for the modules which had the Loss of Communications DTC set. Does the scan tool display any DTCs which do not begin with a "U"? | Go to Control Module References in Body Control System | Go to Step 9
9 |

1. Use the scan tool in order to clear the DTCs.
2. Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared.

Did you complete the action?

Go to Control Module References in Body Control System

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