What Does U0066 Mean?
The positive wire (Bus E+) of the communication bus has an open circuit, meaning the circuit is broken or disconnected. This prevents proper differential signaling required for network communication.
Safety Warning
Complete communication loss will prevent vehicle operation or disable critical safety systems. Vehicle should not be driven until repaired as multiple safety systems may be non-functional.
Common Causes
40%
Broken or severed positive wire in Bus E twisted pair harness
30%
Loose or disconnected connector terminal on Bus E positive circuit
15%
Failed termination resistor causing open circuit condition on positive line
10%
Corroded connector pins creating high resistance appearing as open circuit
5%
Damaged splice point or junction in positive wire circuit
Diagnostic Steps
1
Step 1: Locate Bus E wiring diagram and identify all connection points for the positive wire
2
Step 2: Perform continuity test on Bus E positive wire from end to end with ignition off and modules disconnected
3
Step 3: Inspect all connectors along Bus E positive circuit for backed-out pins or damaged terminals
4
Step 4: Check termination resistors at both ends of Bus E network for proper connection and resistance values
5
Step 5: Repair or replace identified open circuit in positive wire and verify communication is restored
Estimated Repair Cost
$100 - $800
Parts + labor, varies by vehicle and location
The positive wire (Bus E+) of the communication bus has an open circuit, meaning the circuit is broken or disconnected. This prevents proper differential signaling required for network communication.
The most common cause of U0066 (Vehicle Communication Bus E (+) Open) is: Broken or severed positive wire in Bus E twisted pair harness
Typical repair costs for U0066 range from $100 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Complete communication loss will prevent vehicle operation or disable critical safety systems. Vehicle should not be driven until repaired as multiple safety systems may be non-functional.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0066 to identify the root cause.
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Quick Info
Category
Network
System
Vehicle Communication Network
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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