U0008

High Speed CAN Communication Bus (-) High

Car Fault Codes Network

Can you still drive? With care, short trips only

Who can fix it? Needs a workshop

Typical repair time 1 hour – 5 hours

Typical cost SAR 150 to 3,000

What it means

A module has detected that the (-) wire of the high-speed CAN bus is higher than expected, which usually happens when the wire touches a power circuit or battery voltage. Messages then become corrupted or communication between modules stops. The code is usually stored in another module, and several U codes with it confirm the problem is in the bus rather than one module.

Symptoms5

Several warning lights on the cluster at once.
Scan tool cannot communicate with several modules or the whole bus.
Some gauges stop working or the transmission goes into limp mode.
Hard starting or no start on some vehicles.
Fault appears when a certain electrical device is used or after an accessory install.

Possible causes5

The (-) wire shorted to a nearby power wire through worn insulation.
Water or corrosion inside a connector linking the wire to a nearby power terminal.
An accessory such as an alarm or lighting wired onto the bus wires by mistake.
A module with an internal fault raising the wire voltage.
Harness damage after a collision or a poor earlier repair.

How to diagnose5

Read codes from all modules and note whether communication is lost completely or only with some modules.
Disconnect any added accessories, clear the codes and test again.
Disconnect the battery and check that there is no connection between the (-) wire and any nearby power circuit at the connectors, using the wiring diagram.
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.
Disconnect modules one at a time; if the fault clears after unplugging a module, the problem is that module or its branch.

How to fix5

Remove the accessory wired onto the bus and reconnect it correctly.
Dry and clean the wet connector, and replace corroded terminals.
Separate the wire shorted to power and repair its insulation or replace the damaged section.
Replace the module raising the wire voltage if proven faulty, then program and code it.
Clear codes in all modules and confirm communication returns and the code stays off.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

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

The cost is low for a wrongly wired accessory or a wet connector, rises with the time needed to trace the harness, and is highest if a control module is the cause.

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

What raises the voltage on a bus wire?

Usually a short to a power wire through damaged insulation or water in a connector, or an electrical accessory wired onto the bus wires by mistake.

Can this short damage the modules?

The communication circuit in some modules may be damaged if the short lasts a long time, so fix the cause first, then recheck any module that still does not respond.

Can I drive with this code?

With caution and for a short distance if the engine runs, because the transmission and ABS systems may stop working or run in limp mode.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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