For 1990-2009 cars

The Control Module ID Number list provides a method for determining which module is not communicating. 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. Use the Control Module ID Number list in order to determine which module is not communicating and the Lost Communications with XXX diagnostic table in order to diagnose the malfunction.

Control Module | ID Number
--- | ---
Powertrain Control Module (PCM) | 016
Electronic Brake and Traction Control Module (EBTCM) | 040
Sensing and Diagnostic Module (SDM) | 088
Instrument Panel Cluster (IPC) | 096
Pass Key III Module (PK3) | 192

### 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 module's 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 two seconds. When no message is detected from a learned identification number for five seconds, a DTC U1XXX (where XXX is equal to the three digit identification number) is set.

### Conditions for Running the DTC

• | Voltage supplied to the module is in the normal operating voltage range (approximately 9 - 16 volts).

• | A short to ground or B+ is not present. Diagnostic trouble codes U1300 and U1301 and U1305 are not set.

• | 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 five 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 will clear upon receipt of a scan tool Clear DTCs command.

### Diagnostic Aids

• | An intermittent open between the inoperative module and the splice pack SP205 or may cause this code to set.

• | A poor connection at the inoperative module or the splice pack SP205 may cause this code to set.

• | An intermittent open in the splice pack SP205 may cause this code to set.

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

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. A module which loses power during an ignition cycle will cause other module(s) to set Lost Communication DTCs.

2. A module which loses power during an ignition cycle will cause other module(s) to set Lost Communication DTCs.

3. The malfunction is due to an open in the class 2 serial data circuit or an open in the module.

4. The module which was not communicating may have set Lost Communication DTCs for those modules that it was monitoring.

5. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Test the battery positive voltage circuit(s) and the ignition voltage(s) of the module that is not communicating for an open or a short to ground. Refer to Control Module References for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 2

2 |

1. Turn OFF the ignition.
2. Test the ground circuit(s) of the module that is not communicating for an open. Refer to Control Module References for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 3

3 |

1. Disconnect the splice pack SP205.
2. Inspect for poor connections at the splice pack SP205. Refer to Testing for Intermittent Conditions and Poor Connections and Connector 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 circuit of the module that is not communicating for an open between the module and the splice pack SP205. 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 for poor connections at the battery positive voltage circuit(s), the ignition voltage circuit(s), the ground circuit(s) , and the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 7

Go to Step 6

6 | Replace the module which is not communicating. Refer to Control Module References for the appropriate repair instructions. Did you complete the replacement? | -- | Go to Step 9 | --
7 |

1. Install a scan tool.
2. Turn ON the ignition leaving 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 for the applicable Diagnostic System Check

Go to Step 8

8 | Use the scan tool in order to clear the DTCs. Did you complete the action? | -- | Go to Step 9 | --
9 | Select the Display DTCs function for the module(s) which had the Lost Communication with XXX DTC set. Does the scan tool display any DTCs which do not begin with a U? | -- | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 10
10 |

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?

--

System OK

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