U0071: Vehicle Communication Bus E (-) High

What it means

A high fault is detected on the negative conductor of vehicle communication bus E. The code identifies the conductor fault but not its cause.

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 exchanges messages between connected modules over positive and negative conductors. U0071 indicates that the Bus E negative conductor is above its expected voltage range, a fault that can disrupt communication and make modules on that bus unavailable.

Common causes

Most likely first.

1. Persistent short on the CAN-H wire
2. One module driving bus permanently dominant
3. Gateway module routing CAN messages incorrectly

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 to identify the affected Bus E devices and whether the fault is persistent.
2. Inspect the Bus E negative conductor, connectors, and splices for damage, poor contact, or an unintended connection to a supply.
3. Trace the negative line using the wiring diagram and test for a short to power with the circuit isolated as specified by the manufacturer.
4. Check whether a module is holding the bus in a dominant state by isolating Bus E modules according to the manufacturer's diagnostic procedure.
5. Measure bus termination resistance at the specified points and verify gateway routing if the line wiring and modules do not explain the high reading.

Common fixes

• Repair Bus E negative wiring shorted to a supply.
• Repair poor contacts, damaged splices, or corroded terminals on the negative conductor.
• Repair or replace a module found to be holding Bus E dominant.
• Correct a gateway routing fault or failed termination component identified by testing.

Can I keep driving?

Avoid driving if affected systems include essential controls, warning lights indicate a safety function is unavailable, or the vehicle enters limp mode. A high Bus E negative-line condition can interrupt communication across connected modules.