GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 DTC 🢒 DTC U2105-U2199

Circuit Description

Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC U2105 Lost Communication With Engine Control Module (ECM)
    • DTC U2106 Lost Communication With Transmission Control Module (TCM)
    • DTC U2108 Lost Communication With Electronic Brake Control Module (EBCM)
    • DTC U2112 Lost Communication With Electronic Suspension Control (ESC)
    • DTC U2113 Lost Communication With Sensing and Diagnostic Module (SDM)
    • DTC U2116 Lost Communication With Instrument Panel Cluster (IPC)
    • DTC U2118 Lost Communication With Head Up Display (HUD)
    • DTC U2120 Lost Communication With Dynamic Headlamp Leveling (DHL) Device
    • DTC U2122 Lost Communication With Radio
    • DTC U2124 Lost Communication With Audio Amplifier
    • DTC U2125 Lost Communication With Communication Interface Module (OnStar)
    • DTC U2127 Lost Communication With HVAC
    • DTC U2130 Lost Communication With Driver Door Module (DDM)
    • DTC U2132 Lost Communication With Passenger Door Module (PDM)
    • DTC U2135 Lost Communication With Rear Integration Module (RIM)
    • DTC U2138 Lost Communication With Steering Column Lock Control Module (SCLCM)
    • DTC U2144 Lost Communication With Distance Sensing Cruise Control (DSCC) Module
    • DTC U2162 Lost Communication With Instrument Panel integration Module (IPM)
    • DTC U2163 Lost Communication With Left Rear Door Module (LRDM)
    • DTC U2164 Lost Communication With Right Rear Door Module (RRDM)
    • DTC U2165 Lost Communication With Driver Door Switch (DDS)
    • DTC U2166 Lost Communication With Driver Position Module (DPM)
    • DTC U2167 Lost Communication With Remote Control Door Lock Receiver (RCDLR)
    • DTC U2172 Lost Communication With Digital Radio Receiver (DRR)
    • DTC U2179 Lost Communication With Television Module

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 U2100 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.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

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 Link Connector 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

Important: Use the DTC Descriptor list to determine the module which is not communicating. If there are multiple non-communicating modules on high speed GMLAN, choose the one closest to the data link connector (DLC).

Test the following circuits of the module that is not communicating, for an open or a short to ground:

    • The battery positive circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits
    • The high speed communication enable circuit

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 7

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Test the ground circuits of the module that is not communicating, for an open. Refer to the following:
    3. •  Control Module References for the applicable schematic

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4

Test the high speed and low speed GMLAN serial data circuits, if equipped, of the module that is not communicating, for an open. Refer to the following:

    •  Control Module References for the applicable schematic
    •  Circuit Testing
    •  GMLAN Wiring Repairs

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5

Test the following circuits of the module that is not communicating, for poor connections:

    • The battery positive voltage circuits
    • The battery voltage output circuits
    • The switched battery positive voltage circuits
    • The ground circuits
    • The high speed GMLAN serial data circuits
    • The low speed GMLAN serial data circuits
    • The high speed communication enable circuit

Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

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 replacement, setup, and programming.

Did you complete the replacement?

Go to Step 7

--

7
  1. Reconnect all disconnected modules.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool in order to clear the DTCs.

Does the scan tool still display any other current DTCs?

Go to Diagnostic System Check - Vehicle

System OK