What Does U0009 Mean?
The CAN Low (negative) wire is shorted directly to the CAN High (positive) wire, eliminating the differential voltage that allows network communication. This creates a complete communication bus failure.
Safety Warning
Complete loss of network communication will disable multiple vehicle systems including engine management, transmission control, ABS, stability control, and airbag systems. Vehicle may not start or may shut down unexpectedly.
Common Causes
40%
Damaged wiring harness with CAN High and CAN Low wires touching or shorted together
25%
Crushed or corroded connector causing pin-to-pin short between CAN High and CAN Low
20%
Liquid intrusion in connector or junction box causing short circuit between twisted pair
10%
Failed module with internal short between CAN High and CAN Low circuits
5%
Improper repair or modification creating direct short between bus wires
Diagnostic Steps
1
Step 1: Disconnect all modules from the CAN network and measure resistance between CAN High and CAN Low (should read 60 ohms from terminating resistors, not near 0 ohms)
2
Step 2: Perform a visual inspection of all accessible wiring harnesses, especially near heat sources, moving parts, and sharp metal edges
3
Step 3: If short persists with modules disconnected, systematically isolate sections of the harness by disconnecting intermediate connectors
4
Step 4: Inspect all connectors for liquid intrusion, corrosion, or pushed-back pins causing terminal contact
5
Step 5: Once short is isolated to a section, inspect closely for damaged insulation or use a thermal camera to identify hot spots when system is powered
Estimated Repair Cost
$200 - $2,000
Parts + labor, varies by vehicle and location
The CAN Low (negative) wire is shorted directly to the CAN High (positive) wire, eliminating the differential voltage that allows network communication. This creates a complete communication bus failure.
The most common cause of U0009 (High Speed CAN Communication Bus (-) shorted to Bus (+)) is: Damaged wiring harness with CAN High and CAN Low wires touching or shorted together
Typical repair costs for U0009 range from $200 to $2,000, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Complete loss of network communication will disable multiple vehicle systems including engine management, transmission control, ABS, stability control, and airbag systems. Vehicle may not start or may shut down unexpectedly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0009 to identify the root cause.
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Quick Info
Category
Network
System
Network Communications
Difficulty
Type
Generic (SAE)
Recommended Tools
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