U0146
DTC U0100-U02FF
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
For device DTC descriptors, refer to Control Module U Code List Control Module U Code List.
Diagnostic Fault Information
Circuit/System Description
The serial data circuit is the means by which the devices 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 device for diagnostic purposes and to check for DTCs. When the ignition switch is in RUN, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating properly. When a device stops communicating on the serial data circuit, for example if the device loses power or ground, the state of health message it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices in turn set a DTC associated with the loss of state of health of the non-communicating device. The DTC is unique to the device which is not communicating and one or more devices may set the same exact code. A loss of serial data communications DTC does not represent a failure of the devices 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 device availability has not been received.
Action Taken When the DTC Sets
* Specific subsystems will not function.
* DTC U0100 in the transmission control module will cause the transmission to go into default gears.
* Both DTC U0100 in the transmission control module and DTC U0101 in the engine control module will cause the MIL to illuminate.
Conditions for Clearing the DTC
* The engine control module or transmission control 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 device 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 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.
* A device may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between devices can be temporary with no apparent symptom or complaint; this does not mean the device is faulty. Do not replace a device based only on a history U-code.
* 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 either the low or high speed GMLAN serial data system inoperative. This condition is due to those devices using multiple serial data communication systems.
* Use Data Link References Initial Inspection and Diagnostic Overview to determine what serial data communications the device uses.
* Some devices 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 device.
* Some intermittent communication concerns may be caused by fretting corrosion on the serial data circuit terminals. Inspect all connectors at the device that set the communication DTC, the device that the communication DTC was set against, and any inline harness connectors between the two devices. Do not replace a device based only on fretting corrosion. Refer to bulletin 09-06-03-004 for assistance with the diagnosis and repair of this condition, if applicable.
* This diagnostic can be used for any device that is not communicating, regardless of the type of serial data circuit it is connected to, providing the vehicle is equipped with the device.
Reference Information
Schematic Reference
* Data Communication Schematics [1][2]Electrical Diagrams
* Control Module References Control Module References
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
Description and Operation
Data Link Communications Description and Operation Description and Operation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Determine the device that is not communicating. Refer to Control Module U Code List Control Module U Code List.
2. Verify that DTC U0073, U2100, U0074, U0078, U1814, U2099, B1325, B1330, B1370, B1380, B1424, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, or P0562 is not set.
• If any of the DTCs are set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
• If none of the DTCs are set
3. Verify that DTCs U0125 and U0126 are not set.
• If both of the DTCs are set together
Refer to Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device Scan Tool Does Not Communicate with Chassis High Speed GMLAN Device.
• If both of the DTCs are not set together
4. Engine running for 10 seconds.
5. Ignition ON, engine OFF, verify that DTC U0100-U02FF is not set.
• If the DTC U0100-U02FF is set in any device, except the K17 Electronic Brake Control Module
Refer to Circuit/System Testing.
• If the DTC U0100-U02FF is set in the K17 Electronic Brake Control Module with any symptom byte, except symptom bytes 71, 72, and 74
Refer to Circuit/System Testing.
• If the DTC U0100-U02FF is set in the K17 Electronic Brake Control Module with symptom byte 71, 72, or 74 along with other DTCs set
Diagnose all other DTCs first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
• If the DTC U0100-U02FF is set in the K17 Electronic Brake Control Module with symptom byte 71, 72, or 74 and without other DTCs set
1. Program the K17 Electronic Brake Control Module.
2. Verify the DTC does not set.
• If the DTC sets, replace the K17 Electronic Brake Control Module.
• If the DTC does not set
3. All OK.
• If the DTC U0100-U02FF is not set
6. All OK.
Circuit/System Testing
Note: Use the schematics and connector end views to identify the device's ground, B+, ignition, accessory wakeup serial data, serial data communication enable, and serial data circuit terminals.
1. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect all the harness connectors at the device that is not communicating. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between each ground circuit terminal and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. 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
3. Ignition ON.
4. 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
1. Ignition OFF.
2. 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
1. Ignition OFF.
2. 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
5. Ignition ON.
6. If equipped, verify a test lamp illuminates between each ignition circuit terminal and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. 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
1. Ignition OFF.
2. 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
7. Ignition ON.
8. 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
1. Ignition OFF, disconnect the harness connectors at the control module that controls the ignition circuit.
2. 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
3. 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
9. Ignition OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. It may take up to 2 minutes for all vehicle systems to power down.
10. Test for less than 2 ohms in each of the serial data circuits end to end between the device harness connector and the X84 data link connector terminals listed below.
* Low speed GMLAN serial data circuit terminal 1
* High speed GMLAN serial data circuit terminal 6 or 14
* Mid speed GMLAN serial data circuit terminal 3 or 11
* Chassis high speed GMLAN serial data circuit terminal 12 or 13
• If 2 ohms or greater
Repair the open/high resistance in the serial data circuit between the non communicating device and the device setting the DTC or a serial data splice pack.
• If less than 2 ohms
Note: The following test step is only applicable to high speed GMLAN devices.
11. Test for 110-130 ohms between each pair of high speed GMLAN serial data circuits.
• If less than 110 ohms
Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with High Speed GMLAN Device to test for a short to ground or a short between the serial data circuits.
• If greater than 130 ohms
Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with High Speed GMLAN Device to test for an open/high resistance in the serial data circuit.
• If between 110-130 ohms
12. Replace the device that is not communicating.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* GMLAN Wiring Repairs GMLAN Wiring Repairs
* Control Module References Control Module References for device replacement, programming and setup