U0068: Vehicle Communication Bus E (+) High

What it means

Bus E high-side line voltage above expected range. 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

Bus E carries messages between the modules connected to that network, using separate positive and negative conductors. A control module monitors the Bus E positive conductor and sets U0068 when its voltage stays above the expected range, potentially interrupting messages across the bus.

Common causes

Most likely first.

1. Wire shorted to battery
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. Scan all modules and save freeze-frame data and communication codes first to identify which modules stopped responding and when.
2. Inspect the Bus E harness and connectors for damage, corrosion, or a positive-line wire contacting a battery supply.
3. Use the vehicle wiring diagram to identify Bus E, then check its positive conductor for a short to power with the circuit isolated as specified by the manufacturer.
4. Measure the bus termination resistance at the specified points and compare it with the manufacturer's specification.
5. If wiring and termination check out, investigate gateway routing and isolate Bus E modules according to the manufacturer's diagnostic procedure to find a module or connection driving the line high.

Common fixes

• Repair Bus E positive wiring shorted to a battery supply.
• Clean, secure, or replace a damaged Bus E connector.
• Restore correct bus termination by repairing the affected connection or replacing the faulty terminating component.
• Repair or replace a faulty gateway or Bus E module after circuit checks identify it.

Can I keep driving?

Avoid driving if affected systems are unreliable, warning lights indicate a safety function is unavailable, or the vehicle enters limp mode. The high Bus E positive-line voltage can interrupt communication and disable connected functions.