Chevrolet Trax: Scan tool does not communicate with chassis high 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 chassis high speed GMLAN bus functions the same as the primary high speed
GMLAN bus, and the two
buses operate in parallel. The chassis high speed GMLAN bus is added to reduce
message congestion on the
primary high speed bus. Since the chassis high speed GMLAN bus and primary high
speed GMLAN bus
operate in the same manner, the diagnostics for each are the same.
The serial data is transmitted on two twisted wires that allow speeds up to 500
kbit/s. The twisted pair is
terminated with two 120 ohms resistors, one is internal to the electronic brake
control module and the other can
be a separate resistor in a connector assembly or in another device. The
resistors are used as the load for the
chassis high speed GMLAN bus during normal vehicle operation. The chassis high
speed GMLAN is a
differential bus. The chassis high speed GMLAN serial data bus (+) and chassis
high speed GMLAN serial data
(-) are driven to opposite extremes from a rest or idle level of approximately
2.5 V. Driving the lines to their
extremes, adds 1 V to the chassis high speed GMLAN serial data bus (+) circuit
and subtracts 1 V from the
chassis high speed GMLAN serial data bus (-) circuit. If serial data is lost,
devices will set a no communication
code against the non-communicating device. Note that a loss of serial data 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 UCircuit code present.
However, there is no associated "current" or "active" status.
Loss-of-communication Ucodes
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 reinitialize
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 some devices and the scan tool
with one or more GMLAN
serial data systems inoperative. This condition is due to those devices
using multiple serial data
communication systems.
- An open in the DLC ground circuit terminal 5 will allow the scan tool to
operate but not communicate
with the vehicle.
- Technicians may find various Local Area Network (LAN) communication
Diagnostic Trouble Codes
(DTC).
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
- Ignition ON.
- Verify two or more devices are not communicating on the chassis high
speed GMLAN serial data circuit.
Refer to Data Link References to determine how many devices should be
communicating on the bus.
If only one device is not communicating
Refer to Circuit/System Testing - Testing the Device Circuits.
If two or more devices are not communicating
- 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 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 circuits listed below
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, and 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 circuits listed
below 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
- Test for 50-70 ohms between the serial data circuit terminals 12 and 13.
If less than 35 ohms
There may be a third terminating resistor between the serial data circuits.
This can happen if the
incorrect device is installed. Some devices are available with and without the
terminating resistors
installed to reduce the need of terminating resistors in the wiring harness.
Refer to Circuit/System
Testing - Testing the Serial Data Circuits for a Short between the Circuits.
If greater than 70 ohms but less than infinite
Refer to Circuit/System Testing - Testing the Serial Data Circuits for an
Open/High Resistance
If infinite resistance
Repair the open/high resistance in the circuit between the X84 Data Link
Connector and the first
splice/device in the serial data circuit.
If between 50-70 ohms
- Refer to Circuit/System Testing - Testing the Device Circuits.
Circuit/System Testing
NOTE: Each device may need
to be disconnected to isolate a circuit fault.
Use the schematic to identify the following:
- Chassis high speed GMLAN devices the vehicle is equipped with
- Chassis high speed GMLAN serial data circuit terminating resistors
- Device locations on the chassis high speed GMLAN serial data circuits
- Each device's ground, B+, ignition, and chassis high speed GMLAN
serial
data circuit terminals
Some devices with an internal terminating resistor have a loop in the
harness that connects the internal terminating resistor to the
serial data circuit. When
wired this way, test these loop circuits for the appropriate failure mode short
to
voltage, short to ground, or open/high resistance prior to replacing the device
for each of the following tests.
Testing the Serial Data Circuits for a Short to Voltage
- Ignition OFF, disconnect the harness connectors with the chassis high
speed GMLAN serial data circuits
at an easily accessible device, ignition ON.
- Test for greater than 4.5 V between each serial data circuit at the
device connector that was just
disconnected and ground.
If each serial data circuit is 4.5 V or less
- Ignition OFF.
- Test for less than 10 ohms between each of the device's ground circuit
terminals and ground.
- If 10 ohms or greater, repair the open/high resistance in the circuit.
- If less than 10 ohms, replace the device that was disconnected.
If any serial data circuit is greater than 4.5 V
- Ignition OFF, disconnect the harness connectors with the chassis high
speed GMLAN serial data circuits
at another device, in the direction of the circuit shorted to voltage,
ignition ON.
- Test for greater than 4.5 V between each serial data circuit at the
device connector that was just
disconnected and ground.
If each serial data circuit is 4.5 V or less
- Ignition OFF.
- Test for less than 10 ohms between each of the device's ground circuit
terminals and ground.
- If 10 ohms or greater, repair the open/high resistance in the circuit.
- If less than 10 ohms, replace the device that was disconnected.
If any serial data circuit is greater than 4.5 V
- Repeat step 3 until one of the following conditions are isolated:
- A short to voltage on the serial data circuit between two devices or
splice packs, if equipped.
- A short to voltage on the serial data circuit between a device and a
terminating resistor.
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. It may take up to 2 minutes for all vehicle systems to power
down.
- Disconnect the harness connectors with the chassis high speed
GMLAN serial data circuits at an easily
accessible device.
- Test for greater than 100 ohms between each serial data circuit at the
device connector that was just
disconnected and ground.
If each serial data circuit is 100 ohms or greater
Replace the device that was disconnected.
If any serial data circuit is less than 100 ohms
- Disconnect the harness connectors with the chassis high speed GMLAN
serial data circuits at another
device, in the direction of the circuit shorted to ground.
- Test for greater than 100 ohms between each serial data circuit at the
device connector that was just
disconnected and ground.
If both serial data circuits are 100 ohms or greater
Replace the device that was disconnected.
If any serial data circuit is less than 100 ohms
- Repeat step 4 until one of the following conditions are
isolated:
- A short to ground on the serial data circuit between two devices or
splice packs, if equipped.
- A short to ground on the serial data circuit between a device and a
terminating resistor.
- A short to ground on the serial data circuit between the X84 Data Link
Connector and the first
device or splice pack.
Testing the Serial Data Circuits for a Short between the Circuits
- Ignition OFF, all access doors closed, all vehicle systems OFF, and 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.
- Disconnect the harness connectors with the chassis high speed GMLAN
serial data circuits at an easily
accessible device that is not communicating.
- Test for greater than 110 ohms between each pair of serial data circuits
at the device connector that was
just disconnected.
If each pair of serial data circuits is 110 ohms or greater
Replace the device that was disconnected.
If any pair of serial data circuits is less than 110 ohms
- Connect the harness connectors at the device that was disconnected.
- Disconnect the harness connectors with the chassis high speed GMLAN
serial data circuits at another
device, in the direction of the circuit shorted together.
- Test for greater than 110 ohms between each pair of serial data circuits
at the device connector that was
just disconnected.
If each pair of serial data circuits is 110 ohms or greater
Replace the device that was disconnected.
If any pair of serial data circuits is less than 110 ohms
- Repeat step 4 until one of the following conditions are isolated:
- Serial data circuits shorted together between two devices or splice
packs, if equipped
- Serial data circuits shorted together between a device and a terminating
resistor.
- Serial data circuits shorted together between the X84 Data Link
Connector and the first device or
splice pack.
- A shorted terminating resistor.
Testing the Serial Data Circuits for an Open/High Resistance
- Ignition OFF, all access doors closed, all vehicle systems OFF, and 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.
- Disconnect the harness connectors with the chassis high speed GMLAN
serial data circuits at an easily
accessible device that is not communicating.
- Test for less than 130 ohms between each pair of serial data circuits at
the device connector that was just
disconnected.
If each pair of serial data circuit is 130 ohms or less
Replace the device that was disconnected.
If any pair of serial data circuits is greater than 130 ohms
- Connect the harness connectors at the device that was disconnected.
- Disconnect the harness connectors with the chassis high speed GMLAN
serial data circuits at another
device, in the direction of the circuit with the open/high resistance.
- Test for less than 130 ohms between each pair of serial data circuits at
the device connector that was just
disconnected.
If each pair of serial data circuits is 130 ohms or less
Replace the device that was disconnected.
If any pair of serial data circuits is greater than 130 ohms
- Repeat step 4 until one of the following conditions are isolated:
- An open/high resistance on the serial data circuit between two devices
or splice packs, if equipped.
- An open/high resistance on the serial data circuit between a device and
a terminating resistor.
- An open/high resistance terminating resistor.
Testing the Device Circuits
- Ignition OFF, all access doors closed, all vehicle systems OFF, and 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.
- Disconnect the harness connectors at an easily accessible device that is
not communicating.
- Test for less than 10 ohms between each ground circuit terminal 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
- If equipped, verify a test lamp illuminates between each B+ circuit
terminal and ground.
If the test lamp does not illuminate and the circuit fuse is good
- Ignition OFF.
- Test for less than 2 ohms in the B+ circuit end to end.
- If 2 ohms or greater, repair the open/high resistance in the circuit.
- If less than 2 ohms, verify the fuse is not open and there is voltage at
the fuse.
If the test lamp does not illuminate and the circuit fuse is open
- Ignition OFF.
- Test for infinite resistance between the B+ circuit and ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- If infinite resistance, replace the disconnected device.
If the test lamp illuminates
- Ignition ON.
- If equipped, verify a test lamp illuminates between each ignition
circuit terminal, which has a fuse in the
circuit, and ground.
If the test lamp does not illuminate and the circuit fuse is good
- Ignition OFF.
- Test for less than 2 ohms in the ignition circuit end to end.
- If 2 ohms or greater, repair the open/high resistance in the circuit.
- If less than 2 ohms, verify the fuse is OK and there is voltage at the
fuse.
If the test lamp does not illuminate and the circuit fuse is open
- Ignition OFF.
- Test for infinite resistance between the ignition circuit and ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- If infinite resistance, replace the disconnected device.
If the test lamp illuminates
- If equipped, verify a test lamp illuminates between each ignition
circuit terminal, which is controlled by a
control module, and ground.
If the test lamp does not illuminate
- Ignition OFF, disconnect the harness connectors at the control module
that controls the ignition
circuit.
- Test for infinite resistance between the ignition circuit and ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- If infinite resistance
- Test for less than 2 ohms in the ignition circuit end to end.
- If 2 ohms or greater, repair the open/high resistance in the circuit.
- If less than 2 ohms, replace the control module that controls the
ignition circuit.
If the test lamp illuminates
- Ignition OFF, all access doors closed, all vehicle systems OFF, and 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 less than 130 ohms between each pair of chassis high speed
GMLAN serial data circuits at the
device connector that was just disconnected.
If any pair of serial data circuits is greater than 130 ohms
Repair the open/high resistance in the serial data circuits between the
disconnected device and the
circuit splice in the serial data circuits.
If each pair of serial data circuits is 130 ohms or less
- Replace the device that was disconnected.
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
READ NEXT:
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.
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BODY CONTROL SYSTEM DESCRIPTION AND OPERATION
The body control system consists of the body control module (BCM),
communications, and various input and
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SEE MORE:
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 Descriptor
Re
Removal Procedure
Disconnect the battery negative cable. Refer to Battery Negative Cable
Disconnection and
Connection .
Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle
.
Remove the front bumper fascia opening lower cover. Refer to Front
Bumper Fascia Opening Lower