For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this 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 U0100 00: Lost Communication With Engine/Powertrain Control Module (ECM/PCM)
DTC U0101 00: Lost Communication With Transmission Control Module (TCM)
DTC U0102 00: Lost Communication With Transfer Case Control Module
DTC U0104 00: Lost Communication With Cruise Control Module
DTC U0121 00: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U0140 00: Lost Communication With Body Control Module (BCM)
DTC U0151 00: Lost Communication With Sensing and Diagnostic Module (SDM)
DTC U0151 71: Lost Communication With Restraints Control Module Invalid Serial Data Received
DTC U0151 7F: Lost Communication With Restraints Control Module Erratic
DTC U0155 00: Lost Communication With Instrument Panel Cluster (IPC) Control Module
DTC U0164 00: Lost Communication With HVAC Control Module
DTC U0168 00: Lost Communication With Vehicle Theft Deterrent (VTD) Control Module
DTC U0170 00: Lost Communication With Passenger Presence System (PPS)
DTC U0184 00: Lost Communication With Radio
DTC U0194 00: Lost Communication With Digital Radio Receiver (DRR)
DTC U0198 00: Lost Communication With Communication Interface Module (OnStar®)
DTC U0209 00: Lost Communication With Heated Seat Module (HSM)
DTC U0214 00: Lost Communication With Remote Function Actuator (RFA)
DTC U2105 00: Lost Communication

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Low Speed GMLAN Serial Data | 1 | U0140-U0214 | 1 | --
Battery Positive Voltage Circuits | U0100-U0214 | U0100-U0214 | -- | --
Ignition Voltage Circuits | U0100-U0214 | U0100-U0214 | -- | --
Module Ground Circuits | -- | U0100-U0214 | -- | --
Accessory Wakeup Serial Data | U1814 | U0100, U0101 | -- | --
Serial Data Communication Enable | U2099 | U0121 | -- | --
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 serial data communication enable and the accessory wakeup serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The serial data communication enable circuit wakes up the electronic brake control module (EBCM) for buss communication and the accessory wakeup 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 master 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.

### 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.

### Reference Information

#### Schematic Reference

• | Data Communication Schematics

• | Control Module References

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs