U0074

Control Module Communication Bus "B" Off

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

The module storing this code has shut off its own communication on bus "B" after detecting too many transmit errors in a row, a protective state known as bus off. The manufacturer defines which network is bus "B"; on many vehicles it is a second CAN bus. The cause is usually a fault in the bus wiring or the module power supply, and when several modules store the code along with other U codes, the problem is the bus itself rather than one module.

Symptoms5

Check engine light or several warning lights on at once.
Functions of the module storing the code stop or run in limp mode.
Lost-communication codes in other modules.
Scan tool cannot communicate with some modules.
An intermittent fault that comes and goes in some cases.

Possible causes6

Weak battery or unstable voltage while running.
Corroded or loose connector at the module storing the code or at another module on the bus.
Open or shorted wires on bus "B".
Poor module ground.
Another faulty module sending bad messages and disturbing the bus.
Internal fault in the communication circuit of the module storing the code.

How to diagnose6

Identify the module or modules storing the code, and check the manufacturer diagram to see which network is bus "B" on your vehicle.
Check the battery and terminals and measure voltage with the engine off and running.
If only one module stores the code, check its power, ground and connector first.
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 on the bus one at a time to find a disruptive module if there is one.
Inspect connectors exposed to water and wiring at chafe points.

How to fix6

Charge or replace the battery and clean its terminals.
Clean and tighten connectors and repair ground points.
Repair open or shorted bus wires.
Update the module software if the manufacturer has released an update for this problem.
Replace the module proven faulty, then program and code it.
Clear codes in all modules and confirm the code does not return.

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 battery or connector, rises with wiring tracing or a software update, and is highest 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

What does bus off mean?

When a module sees too many transmit errors in a row, it stops communicating on the bus to protect it from disruption, tries to rejoin later, and stores this code.

Is the module that stored the code the faulty one?

Not necessarily. The module stores the code because it was affected. The cause is often wiring, power or another module, especially when more than one module stores the code.

Which network is bus "B"?

It depends on the manufacturer. On many vehicles it is a second CAN bus; check the manufacturer diagram to be sure.

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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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