U0004 — High Speed CAN Communication Bus (+) Low

What Does U0004 Mean?

U0004 is a diagnostic trouble code indicating: High Speed CAN Communication Bus (+) Low. This code relates to the network communication system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of U0004

⚠️ Check Engine Light (MIL) illuminated
⚠️ High Speed CAN Communication Bus (+) Low not functioning as expected
⚠️ Related system may be in fail-safe mode
⚠️ Multiple warning lights on dashboard

Common Causes

🔍 Faulty High Speed CAN Communication Bus (+) Low
🔍 Wiring or connector issue in High Speed CAN Communication Bus (+) Low circuit
🔍 Related mechanical or electrical fault
🔍 ECM/PCM issue (rare)

Frequently Asked Questions

What does U0004 mean?

U0004 indicates: High Speed CAN Communication Bus (+) Low. The vehicle's computer has detected that the High Speed CAN Communication Bus (+) Low is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code U0004?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with U0004 for extended periods may cause additional problems.

How much does it cost to fix U0004?

Repair costs for U0004 typically range from $100 to $500, depending on the root cause. Simple wiring or connector repairs are on the lower end, while component replacement costs more. A proper diagnosis ($80–$150 at most shops) will identify the exact cause before committing to expensive parts.

What To Do Next

Possible Fixes

🔧 Inspect High Speed CAN Communication Bus (+) Low and related wiring
🔧 Replace faulty High Speed CAN Communication Bus (+) Low

1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

U0004: High Speed CAN Communication Bus (+) Low