U0297 indicates that a communication fault has been detected between the vehicle's primary control module (often the PCM or BCM) and the DC/DC converter control module B. This module is typically responsible for stepping down high-voltage DC to low-voltage DC in hybrid or electric vehicles. The code sets when expected data messages are not received over the CAN bus for a specified period.
The most common cause is a poor electrical connection at the module itself, including bent pins, corrosion, or a loose connector. Wiring harness chafing or breaks in the CAN bus twisted pair near the module are also frequent.
A short to power, ground, or an open circuit on the CAN High or CAN Low lines between the DC/DC converter module B and the rest of the network can prevent communication. This often results from harness damage due to heat, vibration, or accident repair.
The module requires a stable power supply and ground to communicate. A blown fuse, corroded ground point, or broken power feed wire will render the module unresponsive.
Internal failure of the module itself, such as water intrusion, overheating, or component failure, can cause it to stop communicating. This is less common than wiring issues but should be considered after verifying circuits.
A different module on the same CAN bus may be pulling the network voltage high or low, disrupting communication for all modules. This can be identified by checking for other communication codes or using a scope to monitor bus activity.
The PCM or a gateway module may fail to relay messages properly. This is a rare cause and should only be suspected after exhaustive testing of the DC/DC converter module, its circuits, and the network.
It depends on the vehicle's design. If the DC/DC converter is not functioning, the 12V battery may not charge, leading to a dead battery and potential stalling. It is advisable to address the issue promptly.
Almost never. The PCM sets this code because it cannot communicate with the DC/DC converter module B. The fault is usually in the converter module itself, its wiring, or its power supply. Replacing the PCM without proper diagnosis is a common misstep and rarely fixes the problem.
In hybrid and electric vehicles, the DC/DC converter steps down high-voltage from the traction battery to charge the 12V battery and run low-voltage accessories. 'Module B' indicates a secondary or specific converter unit. The control module manages this process and communicates status over the CAN bus.
Yes, a severely discharged or failed 12V battery can cause multiple communication codes, including U0297, because modules may not power up correctly. Always test the 12V battery and charging system first.