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U0012 Generic (SAE) Basic entry

Medium Speed CAN Communication Bus (Open)

Updated 2026-10-02 · Network communication (generic)

Severity
Medium
Typical repair cost
50 – 700 EUR
System
Network

What it means

U0012 indicates a fault on the vehicle communication bus itself rather than in one component: Medium Speed CAN Communication Bus ( ). Several modules may log related codes at the same time.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

  • Several warning lights on at the same time
  • Functions controlled by the affected module do not work
  • Scan tool cannot communicate with one module
  • Gauges dropping to zero or dashboard flickering

Common causes

  1. Blown fuse or no power supply to the Medium Speed CAN Communication Bus ( )
  2. Poor ground for the module
  3. Damaged CAN/data bus wiring or connector
  4. Failed module
  5. Low battery voltage during cranking or after a jump start

How to diagnose

  1. Check which modules respond to a full system scan and which do not
  2. Verify fuses, power and ground at the Medium Speed CAN Communication Bus ( ) connector
  3. Measure CAN bus resistance between the two bus wires (about 60 ohms with the battery disconnected) and inspect the wiring
  4. Check battery voltage and charging system; low voltage causes many communication codes
  5. Replace or reprogram the module only after power, ground and bus wiring are confirmed

Frequently asked questions

Can I keep driving with U0012?

Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.

Will clearing U0012 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.

Related codes

U0011U0013U0014U0015

Nearby codes in this group