What Does U0299 Mean?
Communication has been lost with the secondary DC to DC Converter Control Module B. In redundant systems, this backup converter ensures continuous 12V power supply if the primary converter fails.
Common Causes
35%
Damaged wiring or corroded connectors to DC-DC converter module B
30%
Failed DC to DC Converter Control Module B
15%
Module B in standby mode due to primary converter operation (false code)
12%
Thermal protection activation due to cooling system fault
8%
Power distribution fault isolating module B from HV bus
Diagnostic Steps
1
Step 1: Determine if Module B is supposed to be active or in standby; check service information for system architecture
2
Step 2: Compare Module A and Module B status to determine if this is a redundancy system or active parallel operation
3
Step 3: Inspect Module B physical condition, connectors, and mounting for damage or environmental contamination
4
Step 4: Test high-voltage input power availability to Module B and verify isolation/contactor operation
5
Step 5: Verify communication circuit continuity and signal quality; reprogram or replace module if hardware is intact
Estimated Repair Cost
$800 - $3,000
Parts + labor, varies by vehicle and location
Communication has been lost with the secondary DC to DC Converter Control Module B. In redundant systems, this backup converter ensures continuous 12V power supply if the primary converter fails.
The most common cause of U0299 (Lost Communication With DC to DC Converter Control Module "B") is: Damaged wiring or corroded connectors to DC-DC converter module B
Typical repair costs for U0299 range from $800 to $3,000, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may continue operating on Module A, but loss of redundancy increases risk of 12V system failure. Should be repaired to restore system backup capability.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0299 to identify the root cause.
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Quick Info
Category
Network
System
High Voltage to Low Voltage Power Conversion
Difficulty
Type
Generic (SAE)
Recommended Tools
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