Low Speed CAN Communication Bus
What it means
A module has detected a fault on the low-speed CAN bus, a secondary network some makers use for body and comfort modules such as the doors, seats, lighting and climate control. How this bus is built varies by make: on some vehicles it is a single wire and on others two wires, and the modules on it also differ. The code is usually stored in another module, and several U codes together point to a problem with this bus or its power supply.
Symptoms5
- Some comfort functions stop working, such as power windows, mirrors or central locking.
- A/C, interior lights or some control buttons not working normally.
- Warning messages or some indicators not working on the cluster.
- Scan tool cannot communicate with some body modules.
- Battery drain while parked in some cases, because some modules do not go to sleep.
Possible causes6
- Weak battery or unstable voltage.
- Wet or corroded connector, especially in the doors, under the carpet or near the sunroof.
- Broken wires in the flexible door boot from repeated opening and closing.
- Open or shorted bus wiring from chafing or accessory installs.
- A module with an internal fault disturbing the bus, such as a door or seat module.
- Poor ground at one of the modules.
How to diagnose5
- Read codes from all modules and identify the modules on the low-speed bus for your vehicle from the manufacturer diagram.
- Check the battery and terminals and measure voltage.
- Inspect wiring in the flexible door boots and connectors exposed to water.
- Disconnect modules one at a time and watch for communication to return to find the module causing it.
- Check the bus wire or wires for a short to ground or power, and compare readings with the manufacturer specification because the bus design differs between makers.
How to fix6
- Charge or replace the battery and clean its terminals.
- Dry and clean wet connectors, and fix the source of the water leak.
- Repair broken wires in the door boot or anywhere else.
- Remove any electrical accessory causing interference.
- Replace the module proven to be disrupting the bus, then program and code it.
- Clear codes in all modules and confirm the code does not return.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
The cost is low for a battery or a wet connector, rises if door-boot wiring repair or long tracing is needed, 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
Does this code affect driving?
Usually not, because this bus serves body and comfort modules, but some functions may stop and warning messages may appear.
Why does the test method differ between vehicles?
Some makers build this bus with one wire and others with two, and the modules on it differ, so the manufacturer diagram must be used.
Can this fault drain the battery?
Yes, sometimes. If a module stays awake because of the bus fault, it can drain the battery during long parking.
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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