U0020

Low Speed CAN Communication Bus Performance

Car Fault Codes Network

Can you still drive? Yes, normally

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 low-speed CAN bus is working but with message errors or dropouts, without a complete loss. This bus usually serves body and comfort modules, and its design and the modules on it vary by make. The usual cause is an intermittent connection at a connector or wire, or unstable voltage, and the code is usually stored in another module.

Symptoms5

Comfort functions that sometimes work and sometimes stop, such as windows or central locking.
Intermittent warning messages on the cluster.
Delayed response from some buttons or functions.
Intermittent lost-communication codes with body modules.
Sometimes no clear symptom other than the stored code.

Possible causes6

Loose or corroded connector causing an intermittent connection.
Partly damaged wires in the flexible door boot.
Low or unstable battery voltage.
Moisture inside a connector or module.
Interference from added electrical accessories.
A module working incorrectly and sending bad messages.

How to diagnose5

Read codes from all modules and note where communication codes repeat.
Check the battery, charging system and voltage stability.
Gently wiggle connectors and door-boot wiring while watching communication on the scan tool.
Disconnect electrical accessories temporarily and test again.
Compare bus measurements with the manufacturer specification, because the design differs between makers.

How to fix6

Fix any battery or charging problem.
Clean and tighten connectors and replace loose terminals.
Repair damaged wires in the door boot.
Remove the accessory causing interference.
Update the software of the faulty module, or replace and program it if proven faulty.
Clear the codes and confirm the code does not return in daily use.

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 connector or battery, rises because intermittent faults take longer to trace, 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

How is this code different from U0019?

U0019 describes a general bus fault, while this code means the bus works with errors or dropouts. It is usually an intermittent fault.

Is this code serious?

It usually does not affect driving or safety, but it can disable some comfort functions. It is best fixed before it becomes a complete loss of communication.

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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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