U0066: Open Circuit on Vehicle Bus E
The U0066 code indicates that a control module has detected an open circuit on the vehicle's 'E' communication bus. This means data signals cannot be transmitted over that specific bus due to a physical break in the wiring, a disconnected or corroded connector, or an internal failure in the transceiver of a module connected to that network. The 'Bus E' designation is manufacturer-specific and could refer to a high-speed CAN, low-speed CAN, LIN, FlexRay, or other proprietary network.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Loose, corroded, or disconnected connector at a module on Bus E
- Damaged or missing bus termination resistor
- Internal communication transceiver failure in a module connected to Bus E
- Short to battery or ground on one of the bus lines (may be interpreted as open by detection hardware)
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Loss of communication with modules on Bus E (e.g., ABS, airbag, or infotainment systems)
4. Step-by-Step Diagnosis
Scan all modules for communication faults and verify which modules are offline
Visually inspect Bus E wiring and connectors for damage, corrosion, or disconnection
Measure resistance and voltage on Bus E lines (CAN High/Low or LIN) to identify opens or shorts
Check bus termination resistors for correct resistance (typically 60 ohms on CAN)
Isolate the fault by disconnecting modules one at a time and monitoring bus activity
5. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may still be drivable, but systems relying on Bus E (such as ABS, airbags, or transmission control) may not function properly. It is recommended to diagnose and repair the issue promptly to avoid safety risks.
How much does it cost to fix?▼
Repair costs vary widely depending on the root cause. A simple connector repair may cost $50-$150, while replacing a module or wiring harness can range from $200 to $800 or more.