Data Communications (U029D and U029E only)
DTC U0100-U02FF (U029D and U029E only)
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
DTC U029D 00
- Lost Communication with NOx Sensor Module 1 Malfunction
DTC U029E 00
- Lost Communication with NOx Sensor Module 2 Malfunction
Diagnostic Fault Information
Circuit/System Description
Devices connected to the Powertrain High Speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices 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 device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored DTC.
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.
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
* 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.
* 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.
* Multiple control modules may not communicate due to the serial data circuits being shorted, faulty terminating resistor, corrosion or poor connections in various control module connectors or inline connectors. Refer to bulletin 08-07-30-021 for assistance with the diagnosis and repair of these conditions, if applicable.
Reference Information
Schematic Reference
* Engine Controls Schematics [1][2]Electrical Diagrams
* Data Communication Schematics Electrical Diagrams
* Control Module References Control Module References
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)
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
Verify that DTC U0073, U0074, U2100, U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.
If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
Circuit/System Testing
Note: Use the schematic to identify the device's B+, ignition, ground, and serial data circuit terminals.
U029D
1. Ignition OFF, disconnect the harness connector of the Nitrogen Oxides Sensor 1.
2. Test for less than 10 ohms between the ground circuit terminal 4 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit tests normal, replace the Glow Plug Control Module.
3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 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 tests normal, replace the Glow Plug Control Module.
4. Ignition OFF, disconnect the harness connectors of the control module setting the DTC.
5. Test for less than 2 ohms in each serial data circuit between the Nitrogen Oxides Sensor 1 and the control module setting the DTC.
• If greater than the specified range, test the appropriate serial data circuit for an open/high resistance between the Nitrogen Oxides Sensor 1 and the control module setting the DTC.
6. If all circuits test normal, replace the Nitrogen Oxides Sensor 1.
U029E
1. Ignition OFF, disconnect the harness connector of the Nitrogen Oxides Sensor 2.
2. Test for less than 10 ohms between the ground circuit terminal 4 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit tests normal, replace the Glow Plug Control Module.
3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 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 tests normal, replace the Glow Plug Control Module.
4. Ignition OFF, disconnect the harness connectors of the control module setting the DTC.
5. Test for less than 2 ohms in each serial data circuit between the Nitrogen Oxides Sensor 2 and the control module setting the DTC.
• If greater than the specified range, test the appropriate serial data circuit for an open/high resistance between the Nitrogen Oxides Sensor 2 and the control module setting the DTC.
6. If all circuits test normal, replace the Nitrogen Oxides Sensor 2.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* GMLAN Wiring Repairs GMLAN Wiring Repairs
* Nitrogen Oxide Sensor Replacement - Position 1
* Nitrogen Oxide Sensor Replacement - Position 2
* Control Module References Control Module References for control module replacement, setup, and programming