DTC U2105-U2199
Diagnostic Instructions
DTC Descriptor
Refer to
Control Module U Code List .
Diagnostic Fault Information
Circuit
|
Short to Ground
|
Open/High Resistance
|
Short to Voltage
|
Signal Performance
|
Module B+
|
U2105-U2199
|
U2105-U2199
|
-
|
-
|
Module Ignition
|
U2105-U2199
|
U2105-U2199
|
-
|
-
|
Accessory Wakeup Serial Data
|
U1814
|
U2105-U2199
|
-
|
-
|
Serial Data Communication Enable
|
U2099
|
U2105-U2199
|
-
|
-
|
High Speed GMLAN Serial Data (+)
|
2
|
U2105-U2199
|
2
|
-
|
High Speed GMLAN Serial Data (-)
|
2
|
U2105-U2199
|
2
|
-
|
Low Speed GMLAN Serial Data
|
1
|
U2105-U2199
|
1
|
-
|
Module Ground
|
-
|
U2105-U2199
|
-
|
-
|
1. Scan tool does not communicate with low speed GMLAN device
2. Scan tool does not communicate with high speed GMLAN device
|
|
| |
Circuit/System Description
Control 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 control modules. The control 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 V. |
| • |
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 control 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
control module ignition cycle counter reaches the reset threshold
of 50, without a repeat of the malfunction. |
Diagnostic Aids
| • |
If there are multiple
non-communicating modules choose the one closest to the data link
connector (DLC). |
| • |
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 control 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.
|
| • |
Use
Data Link References to determine if the control module uses
high or low speed GMLAN serial data communications |
| • |
Some control modules may not
have internal protection for specific voltage outputs and may open
a battery positive voltage or ignition voltage source fuse. If a
voltage input fuse is open and no short is found in that circuit,
ensure that no control module output voltage circuit is shorted to
ground before replacing the control module. |
| • |
Some intermittent
communication concerns may be caused by fretting corrosion on the
serial data circuit terminals. Inspect all connectors at the
control module that set the communication DTC, the control module
that the communication DTC was set against, and any inline harness
connectors between the two control modules. Do not replace a
control module based only on fretting corrosion. Refer to bulletin
09-06-03-004 for assistance with the diagnosis and repair of this
condition. |
| • |
This diagnostic can be used
for any control module that should communicate with high or low
speed GMLAN serial data providing the vehicle is equipped with the
option that uses that control module. |
Reference Information
Connector End View Reference
Component Connector End Views
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool References
Control Module References for scan tool information
Circuit/System Verification
| 2. |
Verify that DTC U0073, U2100,
U0074, U0078, U1814, U2099, B1325, B1330, B1370, B1380, B1424,
B1428, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is
not set. |
Circuit/System Testing
Note: Terminal and
connector identifiers will be different depending on the individual
control module being tested. Use Schematic Reference and Connector
End View Reference to identify control module's connector, B+,
ignition, ground, communication enable and serial data circuit
terminals.
| 1. |
Ignition OFF, disconnect the
harness connector at the control module that is not
communicating. |
| 2. |
Ignition OFF, test for less
than 10 Ω between each ground circuit terminal and
ground. |
| ⇒ |
If greater than specified range, test the ground
circuit for an open/high resistance. |
| 3. |
If equipped, ignition ON,
verify that a test lamp illuminates between each B+ circuit
terminal 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 control circuits of the control
module for a short to ground. If the circuits test normal, replace
the appropriate control module. |
| 4. |
If equipped, ignition ON,
verify that a test lamp illuminates between each ignition circuit
terminal and ground. |
| ⇒ |
If the test lamp does not illuminate, test the
ignition circuit for a short to ground or an open/high resistance.
If the circuit fuse is open, also test the control circuits of the
control module for a short to ground. If the circuits test normal,
replace the appropriate control module. |
|
Note: Only the high
speed GMLAN modules have a serial data communication enable circuit
OR an accessory wakeup serial data circuit, and the body control
module is the output for these circuits. Refer to the control
module schematics to identify which control modules have these
circuits. If the control module that is not communicating does not
have a serial data communication enable circuit OR an accessory
wakeup serial data circuit, proceed to step 6.
|
| 5. |
If equipped, ignition ON,
verify that a test lamp illuminates between the communication
enable circuit terminal OR the accessory wakeup circuit terminal
and ground. |
| ⇒ |
If the test lamp does not illuminate, test the
entire circuit, including the B+ circuit to the K9 body control
module, for an open/high resistance or short to ground. If the
circuits test normal, replace the K9 body control module. |
| 6. |
Ignition OFF, disconnect the
harness connectors at the control module setting the DTC.
|
| 7. |
Ignition OFF, all access doors
closed, all vehicle systems OFF, and all keys at least 3 meters
away from vehicle. It may take up to 2 minutes for all vehicle
systems to power down. Test for less than 2 Ω in each GMLAN
serial data circuit between the non-communicating control module
and the control module setting the DTC. |
| ⇒ |
If greater than specified range, test the GMLAN
serial data circuit for open/high resistance. |
| 8. |
If all circuits test normal,
replace the control module that is not communicating. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
|
