U01BD: Lost Communication With DC/DC Converter Control Module C

What it means

Communication with DC/DC Converter Control Module C was not received as expected. This code does not by itself establish the converter's voltage or the effect on other systems.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

DC/DC Converter Control Module C controls or reports a converter that transfers power between vehicle electrical systems. This code sets when the expected network messages from converter module C are missing; it does not establish the converter’s output voltage or prove that other systems have lost power.

Common causes

Most likely first.

1. Module unpowered
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Record freeze-frame data and all module codes, and look for low-voltage or charging warnings that may accompany the communication fault.
2. Use a compatible scan tool to check whether DC/DC Converter Control Module C responds and whether converter status data is available.
3. Inspect the module’s low-voltage power, ground, connectors, and wiring for looseness, corrosion, damage, or water entry.
4. Check the communication branch wiring and connectors for opens, shorts, or poor contact.
5. If supply and wiring are sound, have gateway routing and CAN termination checked against the manufacturer’s specification.

Common fixes

• Restore a poor low-voltage power or ground connection at converter module C.
• Repair damaged communication wiring or connector terminals on its network branch.
• Correct a confirmed gateway routing or configuration fault.
• Repair or replace a CAN terminating resistor if it is outside the manufacturer’s specification.

Can I keep driving?

Because this converter may support vehicle electrical systems, avoid driving if electrical warnings appear, systems shut down, or the vehicle’s operation becomes unpredictable. Have the fault diagnosed promptly; continued operation could leave the vehicle without needed electrical support.