DTC U0100-U02FF
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
|
B+
|
U0100-U02FF
|
U0100-U02FF
|
-
|
-
|
Ignition
|
U0100-U02FF
|
U0100-U02FF
|
-
|
-
|
Accessory Wakeup Serial Data
|
U1814
|
U0100-U02FF
|
-
|
-
|
Serial Data Communication Enable
|
U2099
|
U0100-U02FF
|
-
|
-
|
Chassis High Speed GMLAN Serial Data (+)
|
U0074
|
U0074, U0100-U02FF
|
U0074
|
-
|
Chassis High Speed GMLAN Serial Data (-)
|
U0074
|
U0074, U0100-U02FF
|
U0074
|
-
|
Mid Speed GMLAN Serial Data (+)
|
U0074
|
U0074, U0100-U02FF
|
U0074
|
-
|
Mid Speed GMLAN Serial Data (-)
|
U0074
|
U0074, U0100-U02FF
|
U0074
|
-
|
High Speed GMLAN Serial Data (+)
|
2
|
U0073, U0100-U02FF
|
2
|
-
|
High Speed GMLAN Serial Data (-)
|
2
|
U0073, U0100-U02FF
|
2
|
-
|
Low Speed GMLAN Serial Data
|
1
|
U0100-U02FF
|
1
|
-
|
Ground
|
-
|
U0100-U02FF
|
-
|
-
|
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
The serial data circuit is the means by which the control
modules in the vehicle communicate with each other. Once the scan
tool is connected to the serial data circuit through the data link
connector (DLC), the scan tool can be used to monitor each control
module for diagnostic purposes and to check for diagnostic trouble
codes (DTCs). When the ignition switch is in RUN, each control
module communicating on the serial data circuit sends a state of
health (SOH) message to ensure that the control module is operating
properly. When a control module stops communicating on the serial
data circuit, for example if the control module loses power or
ground, the SOH message it normally sends on the serial data
circuit disappears. Other control modules on the serial data
circuit, which expect to receive that SOH message, detect its
absence; those control modules in turn set a DTC associated with
the loss of SOH of the non-communicating control module. The DTC is
unique to the control module which is not communicating and one or
more control modules may set the same exact code. A loss of serial
data communications DTC does not represent a failure of the control
modules that contain the stored code.
Conditions for Running the DTC
The system voltage is between 9-16 V.
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
| • |
Specific subsystems will not
function. |
| • |
DTC U0100 in the TCM will
cause the transmission to go into default gears. |
| • |
Both DTC U0100 in the TCM and
DTC U0101 in the ECM will cause the malfunction indicator lamp
(MIL) to illuminate. |
Conditions for Clearing the DTC
| • |
The ECM/TCM module turns OFF
the MIL after 4 consecutive ignition cycles that the diagnostic
runs and does not fail. |
| • |
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
| • |
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.
|
| • |
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
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 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. |
| • |
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 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
Schematic Reference
Connector End View Reference
Component Connector End Views
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool Reference
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. |
| 3. |
Engine running for 10
seconds. |
| 4. |
Ignition ON, engine OFF,
verify that DTC U0100-U02FF is not set with symptom byte 00.
|
| ⇒ |
If the DTC U0100-U02FF is set with symptom byte
00, refer to Circuit/System Testing. |
| 5. |
Verify that DTC U0100-U02FF is
not set with symptom byte 71 or 72. |
| ⇒ |
If the DTC U0100-U02FF is set with symptom byte 71
or 72 and without other DTCs set, reprogram the control module. If
the DTC resets, replace the control module. |
Circuit/System Testing
Note: Use the schematic to
identify the following:
| • |
Control modules
the vehicle is equipped with |
| • |
Control module
locations on the low and high speed GMLAN serial data
circuits |
| • |
The control
modules B+, ignition, ground, communication enable and serial data
circuit terminals |
| 1. |
Ignition OFF, disconnect the
harness connector at of the control module that is not
communicating. |
| 2. |
Test for less than 10 Ω
between each ground circuit terminal and ground. |
| ⇒ |
If greater than the 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, test the control circuits of the control
module for a short to ground. If the circuits test normal, replace
the 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, test the control circuits of the
control module for a short to ground. If the circuits test normal,
replace the 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 K9 body control
module is the output for these circuits. Refer to the control
module schematics to identify which control modules have these
circuits.
|
| 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, 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 5 Ω between the
serial data circuit terminals and the appropriate X84 data link
connector (DLC) terminal listed below: |
| |
• |
Class 2 serial data circuit
terminal 2 |
| |
• |
Low speed GMLAN serial data
terminal 1 |
| |
• |
High speed GMLAN serial data
terminal 6 or 14 |
| |
• |
Mid speed GMLAN serial data
terminal 3 or 11 |
| |
• |
Chassis high speed GMLAN
serial data terminal 12 or 13 |
| ⇒ |
If greater than the specified range, test the
serial data circuit for an open/high resistance between the non
communicating control module and a module setting the DTC or a
serial data splice pack. |
|
Note: The following
test step is only applicable to high speed GMLAN modules.
|
| 7. |
Test for less than 130 Ω
between each pair of high speed GMLAN serial data circuits.
|
| ⇒ |
If greater than the specified range, test the
serial data circuits for an 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.
|
