U0004Network Communication
High Speed CAN Communication Bus (+) Low
U0004 means the CAN bus high (+) circuit is reading low, usually shorted to ground. This corrupts communication across the high speed bus.
🚗 Not recommended. A shorted CAN high circuit can disrupt the whole bus and cause drivability problems.
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🎯 Top Causes, Ranked by Likelihood
#1CAN high shorted to ground$50-$500
A short to ground on the CAN high wire pulls the signal low.
#2Damaged wiring or connector$50-$400
Chafed or pinched wiring shorts the circuit.
#3Failed module$300-$1000
A module shorting the CAN high line internally.
🩺 Common Symptoms
- Multiple modules offline
- Warning lights
- Stalling or no-start
- Erratic gauges
- Other U-codes stored
💰 Repair Cost: DIY vs Shop
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🔧 How to Diagnose U0004
1Inspect the CAN high wire for shorts to ground
2Check connectors for damage and corrosion
3Disconnect modules one at a time to isolate a shorted unit
4Repair the fault and re-scan
❓ Frequently Asked Questions
Can I drive with U0004?
Not safely. A shorted CAN high circuit can disrupt communication and cause stalling. Diagnose it first.
What causes U0004?
Usually the CAN high wire shorted to ground, or a module shorting the line internally.
How is U0004 different from U0003?
U0003 is an open on CAN high, while U0004 is CAN high pulled low, typically shorted to ground.
🔗 Related Codes
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