Diagnostic Trouble Code (DTC) U0073
Control Module Communication Bus OFF
Circuit Description
The aim of the CAN network is to allow exchange of information between the Engine Control Module(ECM) and the Transmission Control Module(TCM) numerous data are sent from to select the better gear. On the other side TCM sends information to the ECM (vehicle speed, transmission oil temperature, current gear value,0). The can network is conceived with an unshielded twisted pair of wires in order to reduce effects of engine control interfaces.
The TCM is an electronic unit which selects the correct gear for automatic transmission depending of several parameters. In order to achieved these functions, the TCM receives and sends message to the ECM following a normalized protocol CAN V2.0A.
Conditions for Running the DTC
- Ignition an time is greater than 3 seconds.
- Battery voltage is between 9 V and 16 V.
Conditions for Setting the DTC
- CAN driver set the error.
Action Taken When the DTC Sets
- The Service Vehicle Soon (SVS) Lamp will be illuminated as soon as the error occurs.
- The ECM will record operating conditions at the time the disgnostic fails. This information will be stored in Failure Records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The SVS lamp will turn off after current driving cycle in which the disgnostic runs without a fault.
- A history DTC will clear after 20 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for 10 secponds.
Diagnostic Aids
An Intermittent problem may be caused by a poor connection, rubbed through wire insulation, or wire that is broken inside the insulation.
Any circuitry, that is suspected as causing the complaint, should be thoroughly checked for the following conditions.
- Backed-out terminals
- Improper mating
- Broken locks
- Improperly formed
- Damaged terminals
- Poor terminals to wire connection
- Physical damage to the wiring harness
DTC U0073 - Control Module Communication Bus Off
| Step | Action | Value(s) | Yes | No |
| 1 | Perform the Diagnostic System Check. Is the system check complete? | - | Go to Step 2 | |
| 2 | - Turn the ignition switch to LOCK.
- Install the scan tool to the Data Link Connector (DLC).
- Turn the ignition switch to ON.
Are any Diagnostic Trouble Codes(DTCs) displayed? | - | Go to Step 3 | Try with another scan tool |
| 3 | Refer to the applicable DTC table. Start with the DTC with the lowest numerical value and move up. Is the DTC identified as valid trouble code U0073? | - | Go to Step 4 | Go to Applicable DTC Table |
| 4 | - Turn the ignition switch to LOCK.
- Disconnect the Engine Control Module(ECM) and the Transmission Control Module(TCM).
- Check for an open or a short to ground in the wire between the TCM connector J1 terminal 17 and ECM connector J1 terminal 30.
Is the problem found? | - | Go to Step 6 | Go to Step 5 |
| 5 | Check for an open or short to ground in the wire between the TCM connector J1 terminal 7 and ECM connector J1 terminal 49. Is the problem found? | - | Go to Step 6 | Go to Step 7 |
| 6 | - Change the unshielded twisted pair between TCM and ECM or repair the connector terminal as needed.
- Using the scan tool, clear the DTCs.
- Start the engine and idle at normal operating temperature.
- Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.
Does the scan tool indicate that this diagnostic has run and passed? | - | Go to Step 9 | Go to Step 2 |
| 7 | - Replace the TCM.
- Using the scan tool, clear the DTCs.
- Start the engine and idle at normal operating temperature.
- Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.
Does the scan tool indicate that this diagnostic has run and passed? | - | Go to Step 9 | Go to Step 8 |
| 8 | - Replace the ECM.
- Using the scan tool, clear the DTCs.
- Start the engine and idle at normal operating temperature.
- Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.
Does the scan tool indicate that this diagnostic has run and passed? | - | Go to Step 9 | - |
| 9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC) U0101
Lost Communication with TCM
Circuit Description
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 modules. The 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.
Conditions for Running the DTC
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 Service Vehicle Soon (SVS) Lamp will be illuminated as soon as the error occurs.
- The ECM will record operating conditions at the time the disgnostic fails. This information will be stored in Failure Records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The SVS lamp will turn off after current driving cycle in which the disgnostic runs without a fault.
- A history DTC will clear after 20 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for 10 secponds.
Diagnostic Aids
- A poor connection at the inoperative module may cause this code to set.
- An improperly powered module may cause this code to set.
- If there are multiple non-communicating modules choose the one closest to the data link connector (DLC).
- Some 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 module output voltage circuit is shorted to ground before replacing the module.
- This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module.
DTC U0101 - Lost Communication with TCM
| Step | Action | Value(s) | Yes | No |
| 1 | Did you perform the Diagnostic System Check? | - | Go to Step 2 | |
| 2 | Test the following circuits of the module that is not communicating for an open or a short to ground: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 3 |
| 3 | - Turn OFF the ignition.
- Test the ground circuits of the module that is not communicating for an open.
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 4 |
| 4 | Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Did you find and correct the condition? | - | Go to Step 7 | Go to Step 5 |
| 5 | Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage supply circuits
- The ground circuits
- The high speed GMLAN serial data circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 6 |
| 6 | Replace the module that is not communicating. Did you complete the replacement? | - | Go to Step 7 | - |
| 7 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Setting the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 8 |
| 8 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to Step 9 | - |
| 9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC) U0102
Lost Communication with Transfer Case Control Module (TCCM)
Circuit Description
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 modules. The 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.
Conditions for Running the DTC
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 Service Vehicle Soon (SVS) Lamp will be illuminated as soon as the error occurs.
- The ECM will record operating conditions at the time the disgnostic fails. This information will be stored in Failure Records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The SVS lamp will turn off after current driving cycle in which the disgnostic runs without a fault.
- A history DTC will clear after 20 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for 10 secponds.
Diagnostic Aids
- A poor connection at the inoperative module may cause this code to set.
- An improperly powered module may cause this code to set.
- If there are multiple non-communicating modules choose the one closest to the data link connector (DLC).
- Some 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 module output voltage circuit is shorted to ground before replacing the module.
- This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module.
DTC U0102 - Lost Communication with Transfer Case Control Module (TCCM)
| Step | Action | Value(s) | Yes | No |
| 1 | Did you perform the Diagnostic System Check? | - | Go to Step 2 | |
| 2 | Test the following circuits of the module that is not communicating for an open or a short to ground: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 3 |
| 3 | - Turn OFF the ignition.
- Test the ground circuits of the module that is not communicating for an open.
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 4 |
| 4 | Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Did you find and correct the condition? | - | Go to Step 7 | Go to Step 5 |
| 5 | Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage supply circuits
- The ground circuits
- The high speed GMLAN serial data circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 6 |
| 6 | Replace the module that is not communicating. Did you complete the replacement? | - | Go to Step 7 | - |
| 7 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Setting the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 8 |
| 8 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to Step 9 | - |
| 9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC) U0121
Lost Communciation with ABS Control Module
Circuit Description
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 modules. The 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.
Conditions for Running the DTC
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 Service Vehicle Soon (SVS) Lamp will be illuminated as soon as the error occurs.
- The ECM will record operating conditions at the time the disgnostic fails. This information will be stored in Failure Records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The SVS lamp will turn off after current driving cycle in which the disgnostic runs without a fault.
- A history DTC will clear after 20 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for 10 secponds.
Diagnostic Aids
- A poor connection at the inoperative module may cause this code to set.
- An improperly powered module may cause this code to set.
- If there are multiple non-communicating modules choose the one closest to the data link connector (DLC).
- Some 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 module output voltage circuit is shorted to ground before replacing the module.
- This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module.
DTC U0121 - Lost Communciation with ABS Control Module
| Step | Action | Value(s) | Yes | No |
| 1 | Did you perform the Diagnostic System Check? | - | Go to Step 2 | |
| 2 | Test the following circuits of the module that is not communicating for an open or a short to ground: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 3 |
| 3 | - Turn OFF the ignition.
- Test the ground circuits of the module that is not communicating for an open.
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 4 |
| 4 | Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Did you find and correct the condition? | - | Go to Step 7 | Go to Step 5 |
| 5 | Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage supply circuits
- The ground circuits
- The high speed GMLAN serial data circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 6 |
| 6 | Replace the module that is not communicating. Did you complete the replacement? | - | Go to Step 7 | - |
| 7 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Setting the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 8 |
| 8 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to Step 9 | - |
| 9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC) U0140
Lost Communication with Body Control Module (BCM)
Circuit Description
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 modules. The 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.
Conditions for Running the DTC
- CAN driver set the error.
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 Service Vehicle Soon (SVS) Lamp will be illuminated as soon as the error occurs.
- The ECM will record operating conditions at the time the disgnostic fails. This information will be stored in Failure Records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The SVS lamp will turn off after current driving cycle in which the disgnostic runs without a fault.
- A history DTC will clear after 20 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for 10 secponds.
Diagnostic Aids
- A poor connection at the inoperative module may cause this code to set.
- An improperly powered module may cause this code to set.
- If there are multiple non-communicating modules choose the one closest to the data link connector (DLC).
- Some 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 module output voltage circuit is shorted to ground before replacing the module.
- This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module.
DTC U0140 - Lost Communication with Body Control Module (BCM)
| Step | Action | Value(s) | Yes | No |
| 1 | Did you perform the Diagnostic System Check? | - | Go to Step 2 | |
| 2 | Test the following circuits of the module that is not communicating for an open or a short to ground: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 3 |
| 3 | - Turn OFF the ignition.
- Test the ground circuits of the module that is not communicating for an open.
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 4 |
| 4 | Test the high speed GMLAN serial data circuits of the module that is not communicating for an open. Did you find and correct the condition? | - | Go to Step 7 | Go to Step 5 |
| 5 | Inspect the harness connectors of the module that is not communicating for poor connections and terminal tension at the following circuits: - The battery positive voltage input circuits
- The battery positive voltage output circuits
- The ignition voltage input circuits
- The ignition voltage output circuits
- The switched battery positive voltage supply circuits
- The ground circuits
- The high speed GMLAN serial data circuits
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 6 |
| 6 | Replace the module that is not communicating. Did you complete the replacement? | - | Go to Step 7 | - |
| 7 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Setting the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 8 |
| 8 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to Step 9 | - |
| 9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC) U0402
Invalid Data Received from Transmission Control Module
Circuit Description
The transmission control module (TCM) sends transmission data to the engine control module (ECM). The data is sent to the ECM through a communication network called the GM local area network (LAN). Two circuits are used to communicate LAN data between the ECM and TCM. A fault in the LAN will not cause DTC U0402 to set by itself. If a LAN fault occurs, other DTCs will set in addition to DTC U0402.
If the ECM receives invalid transmission data from the TCM, this DTC sets.
Conditions for Running the DTC
Conditions for Setting the DTC
- The ECM receives no valid transmission data from the TCM.
Action Taken When the DTC Sets
- The Service Vehicle Soon (SVS) Lamp will be illuminated as soon as the error occurs.
- The ECM will record operating conditions at the time the disgnostic fails. This information will be stored in Failure Records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The SVS lamp will turn off after current driving cycle in which the disgnostic runs without a fault.
- A history DTC will clear after 20 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for 10 secponds.
DTC U0402 - Invalid Data Received from Transmission Control Module
| Step | Action | Value(s) | Yes | No |
| 1 | Did you perform the Diagnostic System Check? | - | Go to Step 2 | |
| 2 | - Turn the ignition switch to LOCK.
- Install a scan tool to the data link connector (DLC).
- Turn the ignition switch to ON.
- Observe DTC information with a scan tool.
Did any DTCs display other than U0442? | - | Go to applicable DTC table | Go to Step 3 |
| 3 | - Clear the DTC Information with a scan tool.
- Turn the ignition OFF for at least 30 seconds.
- Start, and allow the engine to idle.
Did DTC U0402 fail this ignition? | - | Go to Step 7 | |
| 4 | Did any transmission control module (TCM) DTCs or any other "U" DTC also set? | - | Go to applicable DTC table | Go to Step 5 |
| 5 | Test the LAN circuits in the wiring harness between TCM and the ECM for a high resistance or a poor connection at the module connectors. Did you find and correct the condition? | - | Go to Step 7 | Go to Step 6 |
| 6 | Replace the ECM. Did you complete the replacement? | - | Go to Step 7 | - |
| 7 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Setting the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 8 |
| 8 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | - | Go to applicable DTC table | System OK |
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