U0022: Low Speed CAN Communication Bus (+) High

What it means

A high signal fault has been detected on the positive 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 passes data between modules on CAN-High (+) and CAN-Low (-). U0022 sets when CAN-High is detected at an abnormally high level, which can indicate that this line is shorted to battery voltage.

Common causes

Most likely first.

1. CAN-High shorted to battery
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. Use a scan tool to save freeze-frame data and all communication codes, and list the low-speed modules that do not respond.
2. Check whether the fault began after harness repairs or accessory work that could have brought CAN-High near a power feed.
3. Inspect the low-speed CAN-High wire and connectors for pinching, exposed conductor, or contact with battery-supply wiring.
4. Power down the network as specified by the manufacturer and test CAN-High for an unintended connection to battery voltage, isolating branches as needed.
5. After ruling out voltage intrusion, verify termination and gateway routing with the vehicle wiring diagram and manufacturer procedure.

Common fixes

• Repair the CAN-High wire shorted to battery supply.
• Replace damaged insulation or connector terminals and secure the harness away from power feeds.
• Repair or replace the terminating resistor only if testing finds it outside specification.
• Correct a confirmed gateway routing problem according to the manufacturer's procedure.

Can I keep driving?

Avoid driving if the affected modules control safety-related functions or if the vehicle behaves unpredictably. If it remains controllable, limit use and have the high CAN-High signal diagnosed soon because it can interrupt several low-speed network functions.