U0049: Vehicle Communication Bus C (+) Low

Bus C high-side line voltage below expected range. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.

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

Most likely causes

• Wire shorted to ground
• Gateway module routing CAN messages incorrectly
• CAN terminating resistor (120 Ω) drifted out of spec

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the battery and terminals, and read the codes from all control modules with a multi-system scanner
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Identify which control module is not responding and check its fuses, power supply, and grounds
4. Disconnect add-on accessories, such as alarms or trackers, and read the codes again
5. Inspect the network connectors for moisture or bent pins
6. Measure the network's resistance and signal using the manufacturer's wiring diagram

Good to know

• Repair difficulty: hard
• It can trigger limp mode.

What each character of U0049 means

• U: Communication network
• 0: Generic code: same on every make
• 0: Subsystem depends on the code range
• 49: Specific fault in that system

Frequently asked questions

Can I keep driving with code U0049?

It depends on which control module has dropped out. If it affects the engine, brakes, or steering, do not continue your trip: call for roadside assistance.

What causes code U0049?

The most common causes are: wire shorted to ground; gateway module routing CAN messages incorrectly; cAN terminating resistor (120 Ω) drifted out of spec.

Related codes

• U0058Vehicle Communication Bus D (+) Low
• U0067Vehicle Communication Bus E (+) Low
• U0079Control Module Communication Bus G Off
• U008CVehicle Communication Bus G (+) Low
• U0095Vehicle Communication Bus H (+) Low

Sources

• github.com: dtc database
• en.wikipedia.org: CAN bus

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.