U0066: Vehicle Communication Bus E (+) Open

What it means

Bus E high-side line open. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

Vehicle communication bus E carries data between the modules connected to that network. The control module sets U0066 when the positive (high-side) bus E conductor is open, interrupting communication along the affected path.

Common causes

Most likely first.

1. Wire broken
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Record all module codes and freeze-frame details first, since multiple bus E communication faults can help identify the affected network segment.
2. Check which bus E modules fail to respond and whether the pattern points to a shared positive-line path.
3. Inspect the bus E positive wire, connectors, and splices for a break, loose pin, corrosion, or damage.
4. With power isolated as specified by the manufacturer, test positive-line continuity and isolate sections to locate the open.
5. Check bus E termination and gateway routing against the manufacturer's procedure after confirming the positive conductor is intact.

Common fixes

• Repair a broken bus E positive wire or splice.
• Clean, secure, or replace a damaged positive-line connector terminal.
• Restore a bus E termination connection if it is outside the manufacturer's specification.
• Repair or replace the gateway only if tests confirm it is routing bus E messages incorrectly.

Can I keep driving?

If bus E linked features or warnings are affected, keep driving to a minimum because connected modules may lose communication or shut down. Stop if an essential function is impaired.