U2401
DTC U2401
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 U2401
- Battery Energy Control Module Dedicated Bus 1 Off
For symptom byte information, refer to Symptom Byte List Symptom Byte List.
Diagnostic Fault Information
Circuit/System Description
The Battery Energy Control Module (BECM) dedicated bus is a communication bus used to communicate between the Battery Energy Control Module and the Hybrid/EV Battery Interface Control Modules inside the Hybrid/EV Battery Pack assembly. The Battery Energy Control Module dedicated bus does not communicate with the scan tool.
This diagnostic is used to check the internal Battery Energy Control Module dedicated bus off. If the transmit error counter of a bus is greater than 255 (carry condition in case of an 8-bit transmit error counter) then the supervisor requests the physical layer to set the bus into the "Bus Off" state. At this time, the Battery Energy Control Module increases its fail count. When this fail count is over X Cal Value (7) during Y Cal Value(10 samples), this fail code will happen.
Conditions for Running the DTC
* Vehicle ON.
* The system voltage is at least 9 V.
Conditions for Setting the DTC
The device setting the DTC has received too many transmit errors on the Battery Energy Control Module dedicated serial data circuits.
Action Taken When the DTC Sets
* DTC U2401 is a type A DTC.
* The Battery Energy Control Module sends all Hybrid/EV Battery Interface Control Module data to Invalid, 0 V, and -40°C (-40°F) on high voltage energy high speed GMLAN bus.
Conditions for Clearing the DTC
* DTC U2401 is a type A DTC.
* No bus off status.
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.
* Do not replace a device reporting a U-code. The U-code identifies which device needs to be diagnosed for a communication issue.
* The engine will not start when there is a total malfunction of the Battery Energy Control Module dedicated bus.
* Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) with the scan tool.
Reference Information
Schematic Reference
* Data Communication Schematics [1][2]Electrical Diagrams
* Hybrid Energy Storage Schematics Hybrid Energy Storage Schematics
* Control Module References Programming and Relearning
Connector End View Reference
Component Connector End Views Hybrid/EV Battery Pack X1
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 Programming and Relearning for scan tool information
Special Tools
EL-48900 - HEV Safety Kit
For equivalent regional tools, refer to Special Tools Tools and Equipment.
Circuit/System Testing
Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.
The High Voltage Disabling procedure includes the following steps:
* Identify how to disable high voltage.
* Identify how to test for the presence of high voltage.
* Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.
Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:
* Safety glasses with appropriate side shields when within 15 meters (50 feet) of the vehicle, either indoors or outdoors.
* Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors.
- Visually and functionally inspect the gloves before use.
- Wear the Insulation gloves with leather protectors at all times when working with the high voltage battery assembly, whether the system is energized or not.
Failure to follow the procedures may result in serious injury or death.
Danger: The Volt Battery Pack will utilize an exchange program. Please consult the most recent revision of bulletin/PI #PIP4841, available in Service Information (SI), for a list of approved Volt Battery Pack service procedures. Components that may be removed and serviced without exchanging the complete battery pack are identified in the bulletin/PI. Please contact the GM Technical Assistance Center if you have any questions.
Note: Each device may need to be disconnected to isolate a circuit fault. Use the schematics and connector end views to identify the following:
* Devices connected to the BECM dedicated serial data circuits
* BECM dedicated serial data circuit terminating resistors
* Device locations on the BECM dedicated serial data circuits
* Each device 5 V reference, low reference, and BECM dedicated serial data circuit terminals
1. Perform the High Voltage Disabling procedure before proceeding with this diagnostic. Refer to High Voltage Disabling High Voltage Disabling.
2. Reconnect the 12 V battery.
3. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors with the BECM dedicated serial data circuits at an easily accessible device that is not communicating. It may take up to 2 minutes for all vehicle systems to power down.
4. Vehicle in Service Mode.
5. Test for less than 4.5 V between each BECM dedicated serial data circuit at the device connector that was just disconnected and ground.
• If 4.5 V or greater
Refer to Testing the Serial Data Circuits for a Short to Voltage.
• If less than 4.5 V
6. Vehicle 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.
7. Test for greater than 100 ohms between each BECM dedicated serial data circuit at the device connector that was just disconnected and ground.
• If 100 ohms or less
Refer to Testing the Serial Data Circuits for a Short to Ground.
• If greater than 100 ohms
8. Test for 110-130 ohms between the BECM dedicated serial data circuits at the device connector that was just disconnected.
• If less than 110 ohms
Refer to Testing the Serial Data Circuits for a Short Between the Circuits.
• If greater than 130 ohms
Refer to Testing the Serial Data Circuits for an Open/High Resistance.
• If between 110-130 ohms
9. Refer to Testing the Device Circuits.
Note: Some Hybrid/EV Battery Interface Control Modules have a loop in the harness that connects its 5 V reference circuit back to another control circuit of the same device. When wired this way, test these loop circuits for the appropriate failure mode short to voltage, short to ground, or open/high resistance prior to replacing the device for each of the following tests.
Testing the Serial Data Circuits for a Short to Voltage
1. Vehicle OFF, disconnect the harness connectors with the BECM dedicated serial data circuits at another device that is not communicating, in the direction of the circuit shorted to voltage, Vehicle in Service Mode.
2. Test for greater than 4.5 V between each BECM dedicated serial data circuit at the device connector that was just disconnected and ground.
• If each serial data circuit is 4.5 V or less
Replace the device that was just disconnected.
• If any serial data circuit is greater than 4.5 V
3. Repeat step 1 until one of the follow conditions are isolated:
* A short to voltage on the BECM dedicated serial data circuit between two devices or splice packs, if equipped.
* A short to voltage on the BECM dedicated serial data circuit between a device and a terminating resistor.
Testing the Serial Data Circuits for a Short to Ground
1. Vehicle 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.
2. Disconnect the harness connectors with the BECM dedicated serial data circuits at another device that is not communicating, in the direction of the circuit shorted to ground.
3. Test for less than 100 ohms between each BECM dedicated serial data circuit at the device connector that was just disconnected and ground.
• If both serial data circuits are 100 ohms or greater
Replace the device that was just disconnected.
• If any serial data circuit is less than 100 ohms
4. Repeat step 1 until one of the following conditions are isolated:
* A short to ground on the BECM dedicated serial data circuit between two devices or splice packs, if equipped.
* A short to ground on the BECM dedicated serial data circuit between a device and a terminating resistor.
Testing the Serial Data Circuits for a Short Between the Circuits
1. Vehicle 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.
2. Connect the harness connectors at the device that was previously disconnected.
3. Disconnect the harness connectors with the BECM dedicated serial data circuits at another device that is not communicating, in the direction of the circuits shorted together.
4. Test for less than 110 ohms between each pair of BECM dedicated serial data circuits at the device connector that was just disconnected.
• If each pair of serial data circuits is 110 ohms or greater
Replace the device that was just disconnected.
• If any pair of serial data circuits is less than 110 ohms
5. Repeat step 1 until one of the following conditions are isolated:
* BECM dedicated serial data circuits shorted together between two devices or splice packs, if equipped.
* BECM dedicated serial data circuits shorted together between a device and a terminating resistor.
* A shorted terminating resistor.
Testing the Serial Data Circuits for an Open/High Resistance
1. Vehicle 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.
2. Connect the harness connectors at the device that was previously disconnected.
3. Disconnect the harness connectors with the BECM dedicated serial data circuits at another device that is not communicating, in the direction of the circuit with the open/high resistance.
4. Test for greater than 130 ohms between each pair of BECM dedicated serial data circuits at the device connector that was just disconnected.
• If each pair of serial data circuits is 130 ohms or less
Replace the device that was just disconnected.
• If any pair of serial data circuits is greater than 130 ohms
5. Repeat step 1 until one of the following conditions are isolated:
* An open/high resistance on the BECM dedicated serial data circuit between two devices or splice packs, if equipped.
* An open/high resistance on the BECM dedicated serial data circuit between a device and a terminating resistor
* An open/high resistance terminating resistor
Testing the Device Circuits
1. Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 meters (9.8 feet) away from vehicle. Disconnect the harness connectors at an easily accessible device that is not communicating. It may take up to 2 minutes for all vehicle systems to power down.
2. Disconnect the harness connectors at an easily accessible device that is not communicating.
3. Test for less than 10 ohms between the low reference circuit terminal and ground, at the device connector that was just disconnected.
• If 10 ohms or greater
1. Vehicle OFF, disconnect the harness connectors at the device that controls the low reference circuit.
2. Test for less than 2 ohms in the low reference circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the device that controls the low reference circuit.
• If less than 10 ohms
4. Vehicle in Service Mode.
5. Test for 4.8-5.2 V between the 5 V reference circuit terminal and ground, at the device connector that was just disconnected.
• If less than 4.8 V
1. Vehicle OFF, disconnect the harness connectors at the device that controls the 5 V reference circuit.
2. Test for infinite resistance between the 5 V reference 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 5 V reference circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the device that controls the 5 V reference circuit.
• If greater than 5.2 V
1. Vehicle OFF, disconnect the harness connectors at the device that controls the 5 V reference circuit, Vehicle in Service Mode.
2. Test for less than 1 V between the 5 V reference circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the device that controls the 5 V reference circuit.
• If between 4.8-5.2 V
6. Vehicle in Service Mode.
7. Test for 4.8-5.2 V between the high voltage fault signal circuit terminal and ground, at the device connector that was just disconnected.
• If less than 4.8 V
1. Vehicle OFF, disconnect the harness connectors at the device that controls the high voltage fault signal circuit.
2. Test for infinite resistance between the high voltage fault signal 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 high voltage fault signal circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the device that controls the high voltage fault signal circuit.
• If greater than 5.2 V
1. Vehicle OFF, disconnect the harness connectors at the device that controls the high voltage fault signal circuit, Vehicle in Service Mode.
2. Test for less than 1 V between the high voltage fault signal circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the device that controls the high voltage fault signal circuit.
• If between 4.8-5.2 V
8. Replace the device that was just disconnected.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* GMLAN Wiring Repairs GMLAN Wiring Repairs
* Control Module References Programming and Relearning for device replacement, programming and setup