Broken or chafed wire in the Bus E positive circuit, often due to flexing at a door hinge or near a seat track; Corroded or loose connector terminal at a module or inline splice on the Bus E positive wire; Failed module on Bus E that internally opens the positive circuit, disrupting communication for others; Rodent damage or physical abrasion that severs the positive bus wire; Water intrusion into a connector causing the positive terminal to corrode and open; Aftermarket accessory improperly spliced into the bus wiring, creating an open or high resistance

DTC codes / U00xx · Network wiring and bus faults / U0066

U0066Vehicle Communication Bus E (+) Open

Q: What does code U0066 mean?

Vehicle Communication Bus E (+) Open. U0066 indicates that the vehicle's communication network has detected an open circuit on the positive (high) side of Bus E, meaning the data wire is physically broken or disconnected somewhere along its path. The computer expects a continuous electrical path for the bus to function, and when that path is interrupted, it logs this code and typically disables communication with the modules on that bus.

U0066 indicates that the vehicle's communication network has detected an open circuit on the positive (high) side of Bus E, meaning the data wire is physically broken or disconnected somewhere along its path. The computer expects a continuous electrical path for the bus to function, and when that path is interrupted, it logs this code and typically disables communication with the modules on that bus.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Multiple warning lights illuminated on the dashboard, often including the check engine light, ABS, and airbag lights
Intermittent or complete failure of modules that share Bus E, such as the body control module or instrument cluster
No-start condition if the bus is critical for immobilizer or powertrain communication
Erratic operation of accessories like power windows, door locks, or climate control
Often no symptoms besides the warning light if the open is on a non-critical segment of the bus

Common causes, most likely first

Broken or chafed wire in the Bus E positive circuit, often due to flexing at a door hinge or near a seat track
Corroded or loose connector terminal at a module or inline splice on the Bus E positive wire
Failed module on Bus E that internally opens the positive circuit, disrupting communication for others
Rodent damage or physical abrasion that severs the positive bus wire
Water intrusion into a connector causing the positive terminal to corrode and open
Aftermarket accessory improperly spliced into the bus wiring, creating an open or high resistance

How to diagnose and fix it

Use a scan tool to read all codes and identify which modules are offline, then consult the factory wiring diagram for Bus E to locate the positive wire and its connectors
Perform a visual inspection of the Bus E positive circuit for obvious damage, corrosion, or loose connectors, especially at flex points and known moisture areas
Measure resistance from the data link connector (DLC) positive terminal to each module on Bus E to check for an open circuit, following the service manual procedure
Disconnect modules one at a time to isolate whether a failed module is pulling the bus positive line open
Repair the open circuit by splicing in a new section of wire with proper crimp connectors and heat shrink, or replace the affected harness section
Clear codes and verify communication with all modules on Bus E using a scan tool, then test-drive to confirm the repair

When Bus E Open Isn't a Simple Wire Break

A module that has lost its power or ground can appear to create an open on the Bus E positive line, so always verify module power and ground before condemning the bus wiring.
The code can be set by a poor connection at the data link connector itself, which is often overlooked because technicians focus on the modules rather than the diagnostic port.
Bus E is sometimes used for non-emissions modules, so the vehicle may run and drive normally with only a warning light, leading owners to postpone repair until a critical system fails.
Aftermarket alarms or remote starters spliced into the bus wiring are a frequent cause of U0066, and the splice may be hidden behind the dash or under a sill plate.
Resistance checks on a live bus can give false readings, so always disconnect the battery and wait for modules to power down before testing the positive circuit with an ohmmeter.

Can I keep driving with U0066?

If the vehicle starts and runs normally, you can drive it to a repair shop, but avoid relying on any features that use Bus E, such as advanced driver aids or certain body functions. If the engine stalls or multiple critical systems fail, stop driving and have the vehicle towed to prevent unsafe operation.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.