High Speed CAN Communication Bus

What it means

There is a fault on the high-speed CAN bus, the main data network that the engine, transmission, ABS and other modules use to talk to each other.

Symptoms

• Many warning lights on
• Gauges dropping out
• Possible no-start or limp mode

Probable causes

Most likely first

1. 1Shorted or open CAN High or CAN Low wire
2. 2Water in a connector
3. 3A failed module pulling the bus down
4. 4Low battery voltage

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Check the battery and charging voltage. Low voltage is the most common cause of communication codes.
3. 3Scan all modules: if one module is missing from the list, focus on its power, ground and connectors.
4. 4Check the fuses that feed the module that is not communicating.
5. 5With the battery disconnected, measure resistance between CAN High and CAN Low at the diagnostic port; about 60 Ω is normal.
6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Repair network wiring
• Disconnect modules one at a time to find one that is pulling the bus down, then replace it