U0026: Low Speed CAN Communication Bus (-) Low

What it means

A low signal fault has been detected on the negative line of the low-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

How it works

The low-speed CAN network sends messages between modules using CAN-High (+) and CAN-Low (-). U0026 indicates that CAN-Low is being detected at an abnormally low signal level, commonly because the negative line is shorted to ground.

Common causes

Most likely first.

1. CAN-Low shorted to ground
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. Save freeze-frame data and all module communication codes, noting which low-speed CAN modules are offline.
2. Check which affected functions share this network and whether the problem began after wiring or accessory work.
3. Inspect CAN-Low wiring and connectors for chafing, crushed insulation, corrosion, or contact with vehicle ground.
4. With power removed according to the manufacturer's procedure, test CAN-Low for a short to ground and isolate network sections to find the fault.
5. After ruling out a CAN-Low ground short, check low-speed termination and gateway routing using the vehicle wiring information.

Common fixes

• Repair CAN-Low wiring that is shorted to ground.
• Repair damaged or corroded CAN-Low terminals and secure the harness away from grounded surfaces.
• Replace the terminating resistor only if network testing finds it outside specification.
• Correct a confirmed gateway routing fault according to the manufacturer's procedure.

Can I keep driving?

Avoid driving if the affected network controls safety-related functions or the vehicle behaves unpredictably. If it remains controllable, keep use limited and arrange prompt diagnosis because the CAN-Low ground fault can disrupt several modules.