High Speed CAN Communication Bus

What it means

A control module has detected a general fault on the high-speed CAN bus, the network that usually links the engine computer (ECU) with the transmission module (TCM), the ABS module and others. The bus is two wires twisted together, a (+) wire and a (-) wire, carrying the same message in mirror form, and an open, a short or a faulty module on them can cut communication. The code is usually stored in a module other than the one causing it, and several U codes together point to a bus or power problem rather than one bad module.

Related codes: U0002U0073U0100U0101U0121U0140

Symptoms5

• Several warning lights on the cluster at once, such as the check engine and ABS lights.
• Transmission in limp mode or shifting abnormally.
• Some gauges, such as the speedometer or tachometer, stop working.
• Scan tool cannot communicate with some or all modules.
• Hard starting or no start in some cases.

Possible causes6

• Weak battery or loose or corroded battery terminals.
• Damaged or corroded connector at one of the modules on the bus.
• Open or shorted bus wires from chafing, an earlier repair or an added accessory.
• Water entering a connector or a module on the bus.
• Poor ground connection at one of the modules.
• A module with an internal fault disrupting the whole bus.

How to diagnose6

1. Read codes from all modules and note which modules do not respond and which report lost communication.
2. Check the battery and terminals, and measure voltage with the engine off and running.
3. With the battery disconnected, measure resistance between the two bus wires: a healthy bus has two 120-ohm termination resistors and reads about 60 ohms; about 120 ohms points to an open or a missing resistor, and near zero points to the two wires shorted together.
4. Note that on some vehicles the diagnostic (OBD) port is on a separate diagnostic bus behind a gateway module, so measurements must be taken at a module connector using the wiring diagram.
5. Visually inspect module connectors and bus wiring for corrosion, water, broken wires or recently added accessories.
6. Disconnect modules one at a time and watch for communication to return to find the module or branch causing it.

How to fix6

1. Charge or replace the battery, and clean and tighten its terminals.
2. Clean corroded connectors and repair weak ground points.
3. Repair the open or shorted bus wire, keeping the two wires twisted together.
4. Remove any added electrical accessory found to be disturbing the bus.
5. Replace the module proven to be disrupting the bus, then program and code it to the vehicle.
6. Clear codes in all modules and confirm communication returns and the code stays off.

Repair cost

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a battery or corroded connector, rises with the time needed to trace the wiring, and reaches the upper end if a module must be replaced and programmed.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions