For 1990-2009 cars

### Circuit Description

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC U0100 Lost Communication With Engine Control Module (ECM)

• | DTC U0101 Lost Communication With Transmission Control Module (TCM)

• | DTC U0104 Lost Communication With Distance Sensing and Cruise Control (DSCC) Module

• | DTC U0121 Lost Communication With Electronic Brake Control Module (EBCM)

• | DTC U0140 Lost Communication With Body Control Module (BCM)

• | DTC U0141 Lost Communication With Instrument Panel Module (IPM)

• | DTC U0181 Lost Communication With Dynamic Headlamp Leveling (DHL) Control Module

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom | DTC Symptom Descriptor
--- | ---
00 | No Additional Information

### Conditions for Running the DTC

• | Voltage supplied to the modules is in the normal operating voltage range.

• | The vehicle power mode requires serial data communication to occur.

• | The DTC U0001 does not have a current status.

### Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

### Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | When the ignition cycle counter has reached the newly set threshold and no trouble occurs repeatedly, the history DTC will be cleared.

### Diagnostic Aids

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

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

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Data Communication Schematics Connector End View Reference: Master Electrical Component List
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Is any DTC set among U2105-2199? | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 3
3 | Important: Use the DTC list in DTC Descriptors 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 for the applicable schematic

• | Circuit Testing

• | Wiring Repairs

Did you find and correct the condition?

Go to Step 8

Go to Step 4

4 |

1. Turn OFF the ignition.
2. Test the ground circuits of the module that is not communicating for an open. If the module is the body control module (BCM), test its class 2 serial data circuit for an open, also.

Refer to the following:

• | Control Module References for the applicable schematic

• | Circuit Testing

• | Wiring Repairs

Did you find and correct the condition?

Go to Step 8

Go to Step 5

5 | Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Refer to Circuit Testing and GMLAN Wiring Repairs . Did you find and correct the condition? | Go to Step 8 | Go to Step 6
6 | 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

• | High Speed GMLAN Serial Data Circuits

Refer to the following:

• | Control Module References for the applicable schematic

• | Testing for Intermittent Conditions and Poor Connections

• | Connector Repairs

Did you find and correct the condition?

Go to Step 8

Go to Step 7

7 | Replace the module that is not communicating. Refer to Control Module References for replacement, setup, and programming. Is the replacement complete? | Go to Step 8 | --
8 | Clear the DTCs with the scan tool. Does the scan tool still display other current DTCs? | Go to Diagnostic System Check - Vehicle | --