U0020 — Communication problem on low speed CAN bus
The vehicle's low speed CAN network, which connects various control modules, is experiencing communication issues. This can cause some systems to not work properly or lose data exchange. The code appears when the control module detects poor signal quality or interruptions on this communication line.
Common causes
The cause is almost always one of a few things. Here they are — U0020 rarely comes from anything outside this list:
- Damaged or corroded wiring/connectors in CAN bus
- Faulty control module on the low speed CAN network
- Poor ground or power supply to modules
- Interference or shorts in the CAN wiring
- Loose or disconnected connectors
Where to start
In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:
- Inspect and clean CAN bus connectors and wiring
- Check and secure grounds and power supplies
- Use diagnostic tool to identify faulty module
- Repair or replace damaged wiring or connectors
- Replace faulty control module if necessary
That is what holds for U0020 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.
Why TorqFix for your car?
Above is what the code means and why it appears. TorqFix goes further — it gives you specific procedures, torque values, wiring diagrams and pinouts for your exact engine, not generic steps for every car. Real workshop data (127,000+ diagrams, 10,000+ procedures), interpreted by AI in your language.
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Code breakdown
Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
The same code can mean different things on different makes. Match the meaning to your make before acting on it.
Seen a figure that does not match your manual? Write to us — we correct it and note when. support@torqfix.com
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