U0007: High Speed CAN Communication Bus (-) Low

What it means

A low signal fault has been detected on the negative line of the high-speed CAN communication bus. The affected functions depend on the vehicle network layout.

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

The high-speed CAN network carries messages between key control modules, and CAN-L is its negative signal wire. A control module sets U0007 when it detects CAN-L held unusually low, often because the wire is grounded or a connected module's transceiver is pulling it down.

Common causes

Most likely first.

1. CAN-Low shorted to ground
2. Failed transceiver on one module
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 which high-speed CAN nodes stopped responding when U0007 set.
2. Check whether the affected modules share the high-speed CAN branch, then inspect that branch's CAN-L wiring and connectors for damage, corrosion, or contact with ground.
3. With the vehicle powered down as specified by the manufacturer, check CAN-L for an unintended path to ground and compare the result with the manufacturer's specification.
4. Inspect power and ground connections at modules that disappeared from the network, since poor supplies can disrupt their CAN transceivers.
5. Isolate the high-speed CAN branch or modules using the manufacturer's network test procedure to find a transceiver pulling CAN-L low.
6. Check gateway routing or configuration only after the physical CAN-L circuit and connected module transceivers have been assessed.

Common fixes

• Repair a CAN-L wire chafed or pinched against ground.
• Clean and secure corroded or loose high-speed CAN connectors.
• Restore a module's poor power or ground connection.
• Replace a failed module transceiver after confirming it pulls CAN-L low.
• Correct gateway routing or configuration if the wiring and transceivers test correctly.

Can I keep driving?

If steering, braking, or other essential functions are affected, stop driving and arrange recovery; otherwise drive only as needed and cautiously because high-speed network failures can disable systems or trigger limp mode. Continued faults can cause more modules to drop offline.