Chevrolet Trax: Scan tool does not communicate with low speed gmlan device
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.
Diagnostic Fault Information
Circuit/System Description
The serial data is transmitted over a single wire to the appropriate devices.
The transmission speed for GMLAN
low speed is up to 83.33 kbit/s. Under normal vehicle operating conditions, the
speed of the bus is 33.33 kbit/s.
The devices toggle the serial data circuit between 0-5 V during normal
communications. To wake the devices
connected to the low speed GMLAN serial data circuit, a voltage wake up pulse of
10 V is sent out. If serial
data is lost, devices will set a no communication code against the
non-communicating device. A loss of serial
data communications DTC does not represent a failure of the device that set it.
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 device on the data
communication circuit was disconnected while the communication circuit is
awake.
- Power to one or more devices was interrupted during diagnosis
- A low battery condition was present, so some devices stop communicating
when battery voltage
drops below a certain threshold.
- Battery power was restored to the vehicle and devices 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.
Do not replace a device reporting a U code. The U code identifies which
device needs to be diagnosed for
a communication issue.
Communication may be available between the device and the scan tool with the
low speed GMLAN serial
data system inoperative. This condition is due to the device using both the high
and low speed GMLAN
systems.
An open in the low speed GMLAN serial data circuit between the splice pack
and a device will only
affect that specific device. This type of failure will set a loss of
communication DTC for each device
affected, and the other devices will still communicate.
An open in the X84 Data Link Connector (DLC) ground circuit terminal 5 will
allow the scan tool to
operate but not communicate with the vehicle.
The engine may not start when there is a total malfunction of the low speed
GMLAN serial data circuit.
Technicians may find various Local Area Network (LAN) communication Diagnostic
Trouble Codes
(DTC) and no low speed LAN communications with the scan tool.
These conditions may be caused by the installation of an aftermarket
navigation radio device (see
bulletins). Some customers may comment of one or more of the following concerns:
- Vehicle will not crank
- Vehicle cranks but will not start
- Vehicle stability enhancement system warning lights and messages
- PRNDL gear indicator position errors
Reference Information
Schematic Reference
- Data Communication Schematics (Encore), Data Communication Schematics (Trax)
- Control Module References
Connector End View Reference
WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS -
INDEX - ENCORE WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT
CONNECTOR END VIEWS - INDEX - TRAX
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 Reference
Control Module References for scan tool information
Circuit/System Verification
NOTE: Use the schematic to identify the following:
- Devices the vehicle is equipped with
- Device and splice pack locations on the low speed GMLAN serial
data
circuit
- The low speed GMLAN serial data circuit terminals for each device
or
splice pack
- Attempt to communicate with all devices on the low speed GMLAN serial
data circuit. Refer to Data
Link References.
- Verify which devices are communicating on the low speed GMLAN serial
data circuit.
If only one device is not communicating
Diagnose that device only. Refer to DTC U0100-U02FF.
If one or more devices are communicating but not all
Refer to Circuit/System Testing - Testing the Serial Data Circuit for an Open/High
Resistance.
If none of the devices are communicating
- Ignition OFF, all access doors closed, all vehicle systems OFF, all keys
at least 3 m (9.8 ft) away from
vehicle. Disconnect the scan tool from the X84 Data Link Connector. The
following tests will be done at
the X84 Data Link Connector. It may take up to 2 minutes for all vehicle
systems to power down.
- Test for less than 10 ohms between the ground circuit terminal 5 and
ground.
If 10 ohms or greater
- Ignition OFF.
- Test for less than 2 ohms in the ground circuit end to end.
- If 2 ohms or greater, repair the open/high resistance in the circuit.
- If less than 2 ohms, repair the open/high resistance in the ground
connection.
If less than 10 ohms
- Ignition ON.
- Test for less than 4.5 V between the serial data circuit terminal 1 and
ground.
If 4.5 V or greater
Refer to Circuit/System Testing - Testing the Serial Data Circuits for a
Short to Voltage.
If less than 4.5 V
- Ignition OFF, all access doors closed, all vehicle systems OFF, all keys
at least 3 m (9.8 ft) away from
vehicle. It may take up to 2 minutes for all vehicle systems to power down.
- Test for greater than 100 ohms between the serial data circuit terminal
1 and ground.
If 100 ohms or less
Refer to Circuit/System Testing - Testing the Serial Data Circuits for a
Short to Ground.
If greater than 100 ohms
- Disconnect the appropriate harness connector at the first splice pack
closest in the circuit to the X84 Data
Link Connector.
- Test for less than 2 ohms between the X84 Data Link Connector's serial
data circuit terminal 1 and the
splice pack harness connector's serial data input terminal.
If 2 ohms or greater
Repair the open/high resistance in the serial data circuit.
If less than 2 ohms
- Replace the splice pack.
Circuit/System Testing
Testing the Serial Data Circuits for a Short to Voltage
- Ignition OFF, disconnect the appropriate harness connectors at all low
speed GMLAN serial data splice
packs, ignition ON.
- Test for less than 4.5 V between the serial data circuit terminal 1 at
the X84 Data Link Connector and
ground.
If 4.5 V or greater
Repair the short to voltage on the serial data circuit.
If less than 4.5 V
- Test for less than 4.5 V between each low speed GMLAN serial data
circuit at a splice pack and ground.
If any serial data circuit is greater than 4.5 V
- Ignition OFF, disconnect all devices on the failed serial data circuit,
ignition ON.
- Test for less than 1 V between each section of the failed serial data
circuit and ground.
- If 1 V or greater, repair the short to voltage in the circuit
- If less than 1 V
- Connect the splice pack and connect the first device on the failed
serial data circuit, ignition ON.
- Verify the scan tool communicates or not with the low speed GMLAN serial
data circuit.
- the scan tool does not communicate, replace the device that was just
connected.
- If the scan tool communicates and there are more devices to connect,
connect the next device
and repeat step 3.4.
- If the scan tool communicates and there are no more devices to connect
- All OK.
If all serial data circuits are less than 4.5 V
- All OK.
Testing the Serial Data Circuits for a Short to Ground
- Ignition OFF, all access doors closed, all vehicle systems OFF, and all
keys at least 3 m (9.8 ft) away
from vehicle. Disconnect the appropriate harness connectors at all low speed
GMLAN serial data splice
packs.
- Test for infinite resistance between the serial data circuit terminal 1
at the X84 Data Link Connector and
ground.
If less than infinite resistance
Repair the short to ground on the serial data circuit.
If infinite resistance
- Test for greater than 100 ohms between each low speed GMLAN serial data
circuit at a splice pack and
ground.
If any serial data circuit is 100 ohms or less
- Disconnect all devices on the failed serial data circuit.
- Test for infinite resistance between each section of the failed serial
data circuit and ground.
- If less than infinite resistance, repair the short to ground in the
circuit.
- If infinite resistance
- Connect the splice pack and connect the first device on the failed
serial data circuit, ignition ON.
- Verify the scan tool communicates or not with the low speed GMLAN serial
data circuit.
- If the scan tool does not communicate, replace the device that was just
connected.
- If the scan tool communicates and there are more devices to connect,
connect the next device
and repeat step 3.4.
- If the scan tool communicates and there are no more devices to connect
- All OK.
If all serial data circuits are greater than 100 ohms
- All OK.
Testing the Serial Data Circuit for an Open/High Resistance
- Ignition OFF and all vehicle systems OFF, disconnect the splice pack
containing the devices that are not
communicating on the low speed GMLAN serial data circuit.
- Test for less than 2 ohms between the X84 Data Link Connector terminal 1
and the disconnected splice
pack.
If 2 ohms or greater
Repair the open/high resistance in the serial data circuit.
If less than 2 ohms
- Disconnect all devices on the failed serial data circuit.
- Test for less than 2 ohms between each section of the failed serial data
circuit end to end.
If 2 ohms or greater
Repair the open/high resistance in the serial data circuit.
If less than 2 ohms
- Connect the splice pack and connect the first device on the failed
serial data circuit.
- Verify if the device communicates or not with the scan tool.
If the device does not communicates
Replace the device.
If the device communicates and there are more devices to connect
Connect the next device on the failed serial data circuit and repeat step 6.
If all devices are connected and communicating
- All OK.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
- GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs
- Control Module References for device replacement, programming and setup
Data link references
This table identifies which serial data link that a particular device uses
for in-vehicle data transmission. Some
devices may use more than one data link to communicate. Some devices may have
multiple communication
circuits passing through them without actively communicating on that data link.
This table is used to assist in
correcting a communication malfunction. Not all devices listed will be
applicable to all vehicles. Refer to the schematics to
determine which devices apply. For the description and operation of these serial
data
communication circuits, refer to Data Link Communications Description and
Operation.
Data Link References
Repair instructions
BODY CONTROL MODULE REPLACEMENT (ENCORE)
Fig. 21: Body Control Module
Body Control Module Replacement (Encore)
BODY CONTROL MODULE REPLACEMENT (TRAX)
Fig. 22: Body Control Module
Body Control Module Replacement (Trax)
READ NEXT:
BODY CONTROL SYSTEM DESCRIPTION AND OPERATION
The body control system consists of the body control module (BCM),
communications, and various input and
outputs. Some inputs, outputs and messages requi
SEE MORE:
SPECIFICATIONS
FASTENER TIGHTENING SPECIFICATIONS
Fastener Tightening Specifications
SCHEMATIC WIRING DIAGRAMS
WIPER/WASHER WIRINGSCHEMATICS (ENCORE)
Front Wiper/Washer Control and Wiper
Fig. 1: Front Wiper/Washer Control and Wiper
Rear Wiper/Washer Control and Wiper
Fig. 2: Rear Wiper/Washer
NOTE: Examples used in this article are general in nature
and do not necessarily relate
to a specific engine or system. Illustrations and procedures have been chosen
to guide mechanic through engine overhaul process. Descriptions of processes
of cleaning, inspection, assembly and machine shop pract