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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 DeVille 🢒 DTC 🢒 DTC U1001-U1254 Loss of XXX Communications

Refer to Data Link Connector (DLC) Schematics

Power and Ground


Object Number: 475096 Size: FS
Data Link Communications Components
Data Link Communications Circuit Description
Serial Data Class 2 (1 of 3)
G200
G201 - IP Harness
HDHIBML, HDHIBMR, ALDL, PCM BATT, IP Fuses
G201 - IP Harness
G200
Serial Data Class 2 (1 of 3)
 .

Circuit Description

During normal vehicle operation modules connected to the class 2 serial data circuit monitor the class 2 serial data circuit for serial data communications . Operating information and commands are exchanged among the modules. When a module receives a critical operating parameter, the module records and identification number of the transmitting module for the purpose 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 the class 2 serial data circuit for that module's Node Alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. If no message is detected from a learned identification number for 5 seconds, a DTC U1XXX (where XXX is equal to the three digit identification number) is set.

Control Module

ID Number

Powertrain Control Module (PCM)

016

Electronic Brake Control Module (EBCM)

040

Electronic Suspension Control Module

056

Dash Integration Module (DIM)

064

Instrument Panel Module (IPM)

065

Rear Integration Module (RIM)

066

Inflatable Restraint Sensing and Diagnostic Module (SDM)

088

Instrument Cluster

096

Radio

128

Radio Amplifier

129

Cellular Telephone Module

144

Navigation Data Processor

145

Vehicle Interface Unit (VIU)

151

Driver Door Module (DDM)

160

Passenger Front Door Module (PFDM)

161

LH Rear Door Module (LRDM)

162

RH Rear Door Module (RRDM)

163

Driver Door Switch Assembly (DDSA)

164

RH Front Power Window Switch

165

Remote Function Actuator (RFA)

176

Vehicle Theft Deterent Module

192

Conditions for Running the DTC
    • Diagnostic trouble codes B1327, B1328, U1300, U1301, and U1305 do not have a current status. Any particular device on the class 2 serial data circuit will support some subset of these DTCs.
    • 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

When multiple Loss of Communication DTCs are set concurrently, the cause is likely to be two opens in the class 2 serial data circuit. Use the Control Module ID Number list in order to determine which modules are not communicating. Use the class 2 serial data circuit schematic in order to determine the location of the opens.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. The following modules have a single wire connection to the class 2 serial data circuit. An open in the single wire will prevent communications.

    2. • Cellular Telephone Module
    • Electronic Suspension Control
    • Driver Door Module (DDM)
    • Driver Door Switch Assembly (DDSA)
    • LH Middle Door Module (LMDM) (if equipped with V4U)
    • LH Rear Door Module (LRDM)
    • Memory Seat Module (MSM)
    • Navigation Data Proccessor (if equipped with UY4)
    • Passenger Front Door Module (PFDM)
    • Radio (if equipped with UY4)
    • Radio Amplifier
    • Rear Intergration Module (RIM)
    • Rear Heater and A/C Control
    • Remote Function Actuator (RFA)
    • RH Front Power Window Switch (if equipped with armored car)
    • RH Middle Door Module (RMDM) (if equipped with V4U)
    • RH Rear Door Module (RRDM)
    • Steering Column Module
    • Theft Deterrent Module
    • Vehicle Interface Unit (VIU)

  2. The module which was not communicating due to an open in the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.

Step

Action

Yes

No

1

Test the battery positive voltage circuit(s) and the ignition voltage circuit(s) of the the module that is not communicating for an open or a short to ground. For the applicable Schematic, refer to Control Module References . 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 and the module ID (if applicable) circuit(s) of the module that is not communicating for an open. For the applicable Schematic, refer to Control Module References . 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

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(s) 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 9

Go to Step 4

4

Do the following modules, if equipped, communicate with the scan tool?

    • Cellular Telephone Module
    • Driver Door Module (DDM)
    • Driver Door Switch Assembly (DDSA)
    • Electronic Suspension Control
    • LH Middle Door Module (LMDM) (if equipped with V4U)
    • LH Rear Door Module (LRDM)
    • Memory Seat Module (MSM)
    • Navigation Data Proccessor (if equipped with UY4)
    • Navigation Radio (if equipped with UY4)
    • Passenger Front Door Module (PFDM)
    • RH Front Power Window Switch (if equipped with armored car)
    • Radio Amplifier
    • Rear Intergration Module (RIM)
    • Rear Heater and A/C Control
    • Remote Function Actuator (RFA)
    • RH Middle Door Module (RMDM) (if equipped with V4U)
    • RH Rear Door Module (RRDM)
    • Steering Column Module
    • Theft Deterrent Module
    • Vehicle Interface Unit (VIU)

Go to Step 6

Go to Step 5

5

Test the class 2 serial data circuit of the module that is not communicating for an open. For the applicable Schematic, refer to Control Module References . Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6

Replace the module that 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 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 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 Loss of Communications 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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