U0011: Medium Speed CAN Communication Bus Performance

What it means

Performance of the medium-speed CAN communication bus is outside the expected range. The affected functions depend on the vehicle network layout.

How it works

The medium-speed CAN bus carries messages between modules on that network, often body or comfort systems depending on the vehicle. U0011 indicates that bus communication performance is outside the expected range, which can result from corrupted frames, connector corrosion, or incorrect message routing rather than a single specified open or short.

Common causes

Most likely first.

1. Corrosion in body harness connectors
2. One module sending malformed frames
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, communication codes, and any available network status data to see when medium-speed bus performance degraded.
2. Check which MS-CAN modules report missing or invalid messages and whether the affected functions share a branch.
3. Inspect body harness and MS-CAN connectors for corrosion, moisture, loose terminals, or damaged wiring that can distort communication.
4. Check power and ground at modules reported as sending errors, since unstable supplies can corrupt their messages.
5. Use the manufacturer's network diagnostics to assess message quality and isolate a module that may be transmitting malformed frames.
6. Verify gateway routing and configuration after checking the connectors, wiring, and module supplies.

Common fixes

• Clean and secure corroded medium-speed CAN connectors and repair damaged terminals.
• Repair a damaged MS-CAN wire or connector causing intermittent or corrupted communication.
• Correct unstable power or ground to a module sending errors.
• Replace a module only when testing confirms its transceiver or communication circuitry is faulty.
• Correct gateway routing or configuration if the bus and modules are sound.

Can I keep driving?

If affected functions are limited to comfort features and essential controls work normally, cautious driving may be possible, but do not rely on unavailable features. Stop driving if safety-related functions are affected, since poor bus communication can make several modules behave unpredictably.