High Speed CAN Communication Bus (-) Open
What it means
A module has detected that the (-) wire of the high-speed CAN bus is open, meaning it is broken or disconnected somewhere. The bus needs both wires to carry messages correctly, so communication with some modules may stop or become intermittent depending on where the open is. The code is usually stored in another module, and several lost-communication codes together confirm the problem is in the wiring rather than the modules.
Symptoms5
- Several warning lights on the cluster at once.
- Scan tool cannot communicate with one or more modules.
- Transmission in limp mode or some gauges not working.
- No start on some vehicles if communication with the engine computer is lost.
- Lost-communication codes such as U0100 or U0121 in different modules.
Possible causes5
- Loose or pushed-back terminal inside a module connector.
- Connector corrosion from moisture or water entry.
- Broken wire from chafing, strain or a poor earlier repair.
- Damaged splice or junction point inside the harness.
- A module connector left unplugged or not fully seated after service.
How to diagnose5
- Read codes from all modules and identify the ones that do not respond; they are usually on the open side of the bus.
- 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.
- Check continuity of the (-) wire between module connectors using the wiring diagram to locate the open section.
- Inspect the (-) wire terminals at the module connectors for loose, corroded or pushed-back pins.
- Review any recent service work, collision damage or accessories added near the wiring route.
How to fix5
- Reconnect or fully seat the unplugged connector.
- Clean the corroded connector and replace the damaged terminal.
- Repair the broken wire with a sealed, insulated splice, keeping the two wires twisted together.
- Repair the damaged harness splice or replace the damaged harness section.
- 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 if the open is at a visible connector, and rises if it is inside the harness and parts of the vehicle must be removed to reach it. A module replacement is rarely needed.
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 it mean that the (-) wire is open?
The wire is broken or disconnected at some point, so the signal does not reach some modules. The cause is usually a damaged connector or terminal.
How does a resistance reading help find the fault?
A healthy bus reads about 60 ohms between the two wires with the battery disconnected. About 120 ohms or an open reading points to a break, which is then located by measuring the sections between modules.
Do I need to replace a control module?
Rarely. This code points to an open in the wiring or connectors, and repairing it restores communication in most cases without replacing any module.
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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