OBD-II code U0299 indicates that the powertrain control module (PCM) or another control module has lost communication with the DC/DC converter control module 'B' on the vehicle's Controller Area Network (CAN) bus. This typically means the module is not sending or receiving expected messages, disrupting electrical system coordination.
The module itself may have an internal failure, such as a power supply issue, corrupted firmware, or hardware defect, preventing communication on the CAN bus.
Damaged, corroded, or loose wiring or connectors in the CAN bus circuit (e.g., CAN-H, CAN-L, power, or ground) can disrupt communication with the module.
A missing or blown fuse, or a failed relay, can cut power to the DC/DC converter, causing it to stop communicating on the network.
Problems in the CAN bus wiring, such as a short to ground, short to power, or open circuit, can prevent the DC/DC converter from communicating with other modules.
A weak or failing 12-volt battery, or charging system issues, can cause voltage fluctuations that disrupt communication between modules.
While uncommon, a failure in the PCM or another control module on the network could prevent proper communication with the DC/DC converter. This is typically a last-resort diagnosis after other causes are ruled out.
No, the PCM is rarely the cause of U0299. This code typically points to issues with the DC/DC converter control module itself, its wiring, or the CAN bus network. Replacing the PCM should only be considered after all other potential causes have been ruled out.
Driving with U0299 may be possible, but it depends on the vehicle. Some hybrid/electric vehicles may enter a reduced-power mode or disable certain systems to protect components. If the 12-volt battery is not charging properly, the vehicle may stall or fail to restart. It is recommended to diagnose and repair the issue promptly.
U-codes often appear in groups because multiple modules may lose communication if there is a CAN bus network issue. For example, a short or open in the CAN bus wiring can cause several modules to stop communicating, resulting in multiple U-codes. Always diagnose the network as a whole when multiple U-codes are present.
A scan tool capable of reading CAN bus data is highly recommended for diagnosing U0299. It allows you to check for communication with the DC/DC converter, monitor live data, and perform tests like CAN bus resistance measurements. Basic code readers may not provide enough information for a thorough diagnosis.