U0057: Vehicle Communication Bus D (+) Open

What it means

Bus D 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 D carries data between the modules connected to that network. The control module detects that the bus D positive (high-side) conductor is open, interrupting communication on 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 faults reported across several modules can point to a shared bus D problem.
2. Check which modules on bus D fail to respond and whether other bus D faults appear alongside U0057.
3. Inspect the bus D positive wire, connectors, and splices for breaks, loose pins, corrosion, or damage.
4. With the vehicle powered down as specified by the manufacturer, test continuity of the positive conductor and isolate sections to locate an open.
5. Check bus D termination and resistance against the manufacturer's specification, then verify gateway routing only after wiring and termination pass.

Common fixes

• Repair a broken bus D positive wire or damaged splice.
• Clean, secure, or replace a corroded or loose connector terminal on the positive line.
• Restore a bus D terminating resistor or connection that is outside the manufacturer's specification.
• Repair or replace the gateway only if testing confirms it is routing bus D messages incorrectly.

Can I keep driving?

If affected systems still work normally, drive only as needed and watch for new warnings; modules may lose communication and enter limp mode or shut down. Avoid trips that depend on affected functions, and stop if braking, steering, or other essential systems are impaired.