For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using the diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC U2105 00: Lost Communication With Engine Control System
DTC U2106 00: Lost Communication With Transmission Control System
DTC U2107 00: Lost Communication With Body Control System
DTC U2108 00: Lost Communication With ABS/TCS Control System
DTC U2109 00: Lost Communication With Powertrain Control System
DTC U2110 00: Lost Communication With Chassis Multiple Control System
DTC U2111 00: Lost Communication With Steering Control System
DTC U2112 00: Lost Communication With Electronic Suspension Control (ESC)
DTC U2113 00: Lost Communication With Sensing and Diagnostic Module (SDM)
DTC U2114 00: Lost Communication With PPS or CPS
DTC U2115 00: Lost Communication With (Restraints Control System)
DTC U2116 00: Lost Communication With Instrument Panel Cluster (IPC)
DTC U2117 00: Lost Communication With Driver Information Center (DIC)
DTC U2118 00: Lost Communication With Head Up Display (HUD)
DTC U2119 00: Lost Communication With Daytime Running Lamps (DRL) System
DTC U2120 00: Lost Communication With Automatic Headlamp Leveling Device (AHLD)
DTC U2121 00: Lost Communication With Radio Display
DTC U2122 00: Lost Communication With Radio
DTC U2123 00: Lost Communication With Compact Disc Changer (CDX)
DTC U2124 00: Lost Communication With Audio Amplifier
DTC U2125 00: Lost Communication With Telematic Unit
DTC U2126 00: Lost Communication With (Mobile Communications Control System)
DTC U2127 00: Lost Communication With Front HVAC
DTC U2128 00: Lost Communication With Rear HVAC
DTC U2129 00: Lost Communication With Remote Function Actuator (RFA)
DTC U2130 00: Lost Communication With Driver Door Module (DDM)
DTC U2131 00: Lost Communication With Driver Seat Module (DSM)
DTC U2132 00: Lost Communication With Passenger Door Module (PDM)
DTC U2133 00: Lost Communication With Passenger Seat Module (PSM)
DTC U2134 00: Lost Communication With Rear Door Module (RDM)
DTC U2135 00: Lost Communication With Rear Integration Module (RIM)
DTC U2136 00: Lost Communication With Memory Mirror Module (MMM)
DTC U2137 00: Lost Communication With Vehicle Theft Deterrent (VTD)
DTC U2138 00: Lost Communication With Column Locking Module (CLM)
DTC U2139 00: Lost Communication With Column Integration Module (CIM)
DTC U2140 00: Lost Communication With Underhood Electrical Center (UEC)
DTC U2141 00: Lost Communication With Rear Electrical Center (REC)
DTC U2142 00: Lost Communication With Yaw Rate Sensor (YRS)
DTC U2143 00: Lost Communication With Steering Angle Sensor (SAS)
DTC U2144 00: Lost Communication With Distance Sensing Cruise Control Module
DTC U2145 00: Lost Communication With Parking Assistance System (PAS)
DTC U2146 00: Lost Communication With Shift Lever Module (SLM)
DTC U2147 00: Lost Communication With Auxiliary Heater System (AHS)
DTC U2148 00: Lost Communication With Sun Roof Module (SRM)
DTC U2149 00: Lost Communication With Tire Pressure Monitor (TPM) System
DTC U2150 00: Navigation Electronic Control Unit (ECU) Gateway Communications
DTC U2151 00: Navigation Electronic Control Unit (ECU) Communications
DTC U2152 00: Navigation Bus Request Line Circuit Low
DTC U2153 00: Navigation Electronic Control Unit (ECU) - VICS Communication Circuit
DTC U2160 00: Lost Communication With Steering Control System Sensor
DTC U2161 00: Lost Communication With Dash Integration Module (DIM)
DTC U2162 00: Lost Communication With Instrument Panel integration Module (IPM)
DTC U2163 00: Lost Communication With Left Rear Door Module (LRDM)
DTC U2164 00: Lost Communication With Right Rear Door Module (RRDM)
DTC U2165 00: Lost Communication With Driver Door Switch (DDS)
DTC U2166 00: Lost Communication With Driver Position Module (DPM)
DTC U2167 00: Lost Communication With Remote Control Door Lock Receiver
DTC U2168 00: Lost Communication With Side Object Detection (SOD) Module - Left
DTC U2169 00: Lost Communication With Side Object Detection (SOD) Module - Right
DTC U2170 00: Lost Communication With Four Wheel Drive (4WD) Clutch
DTC U2171 00: Lost Communication With Rear Seat Entertainment (RSE)
DTC U2172 00: Lost Communication With Digital Radio Receiver
DTC U2173 00: Lost Communication With Passive Entry and Passive Start System
DTC U2174 00: Lost Communication With Parking Heater System
DTC U2175 00: Lost Communication With Special Vehicle Module
DTC U2176 00: Lost Communication With Power Take Off (PTO) Control Module
DTC U2177 00: Lost Communication With Cruise Control Module
DTC U2178 00: Lost Communication With Trailer Interface Module
DTC U2179 00: Lost Communication With Television Module
DTC U2180 00: Lost Communication With Folding Top Control Module
DTC U2181 00: Lost Communication With Moveable Roof Module

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Low Speed GMLAN Serial Data | 1 | U2105-U2199 | 1 | --
Battery Positive Voltage Circuits | U2105-U2199 | U2105-U2199 | -- | --
Ignition Voltage Circuits | U2105-U2199 | U2105-U2199 | -- | --
Module Ground Circuits | U2105-U2199 | U2105-U2199 | -- | --
Accessory Wake Up Serial Data | U1814 | U2105-U2199 | -- | --
High Speed GMLAN Serial Data Wake Up | U2099 | U2105-U2199 | -- | --
1. Scan tool does not communicate with low speed GMLAN device

### Circuit/System 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.

The body control module (BCM) activates the high speed GMLAN serial data wake up and the accessory wake up serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The high speed GMLAN serial data wake up circuit wakes up the electronic brake control module (EBCM) for bus communication and the accessory wake up serial data circuit wakes up the engine control module (ECM) and transmission control module (TCM).

### Conditions for Running the DTC

• | The system voltage is between 9-16 volts.

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

### 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 parameters.

### 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 of 50, without a repeat of the malfunction.

### Diagnostic Aids

• | Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- | A control module on the data communication circuit was disconnected while the communication circuit is awake.

- | Power to one or more modules was interrupted during diagnosis.

- | A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- | Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- | If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

• | A control module may have a U code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U code.

• | Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.

• | Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

• | Use to determine if the module uses high or low speed GMLAN serial data communications.

• | Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control module.

• | This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to, providing the vehicle is equipped with the control module.

### Reference Information

• | Data Communication Schematics

• | Control Module References

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool References

Control Module References for scan tool information

### Circuit/System Testing

Important: If more than one module is not communicating use Data Communication Schematics to determine which module is closest to the DLC. Start diagnostics with that module.

Terminal and connector identifiers will be different depending on the individual module being tested. Use Schematic Reference and Connector End View Reference to determine which connector and terminal to access.

1. Using the DTC Descriptor and Diagnostic Aids, determine the module that is not communicating that should be tested.
2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
3. Test for less than 2 ohms between the module ground circuits and ground.

⇒ | If greater than specified range, test the ground circuit for an open/high resistance.

Important: Only the high speed GMLAN modules have a wired serial data wake up circuit. Refer to the module schematics to identify which modules have a wake up circuit. If the module that is not communicating does not have a serial data wake up circuit, proceed to step 5.

4. Ignition ON, verify that a test lamp illuminates between the high speed GMLAN serial data wake up circuit OR the accessory wake up serial data circuit and ground.

⇒ | If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

5. Ignition ON, verify that a test lamp illuminates between all B+ circuits and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the appropriate module.

6. Verify that a test lamp illuminates between all ignition voltage circuits and ground.

⇒ | If the test lamp does not illuminate, test the ignition voltage circuits for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the appropriate module.

7. Test for less than 1 ohm in the GMLAN serial data circuits between the non-communicating module and the module that displays the DTC.

⇒ | If greater than specified range, test the GMLAN serial data circuits for open/high resistance.

8. If all circuits test normal, replace the module that is not communicating.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | GMLAN Wiring Repairs

• | Control Module References for module replacement, setup, and programming