U0012 code meaning
Medium Speed CAN Communication Bus (+) Open
What U0012 means
U0012 reports an interruption of CAN-High, the (+) wire of the medium-speed CAN. Saab's mid-speed GMLAN uses the same two-wire layout as the fast bus, with a terminating resistor between (+) and (-), so a break isolates the modules downstream and alters the resistance seen between the lines. Ford's F-Super Duty illustrates the effect at vehicle level: if connector C408 stays unplugged after the pickup box is removed, MS-CAN traffic is cut and climate control, front controls and headlamp logic stop working. No manufacturer documents U0012 with its J2012 meaning; Alfa Romeo uses U0012-14 and -15 for the up circuit of its DNA selector instead. Check terminals and splices of the medium-speed pair, especially at doors, tailgates and upfitter bodies.
U0012 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0012
- Comfort and body modules behind the break inoperative
- Climate, lighting or switch panel functions missing
Common causes of U0012
- Most likelyBody or upfitter connector in the medium-speed (+) path left open
- PossibleCAN-High conductor broken in a door or tailgate harness
- PossibleCorroded or loose CAN-High terminal
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
CAN high wireModule connector
What each part of U0012 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 12 | The exact fault in that area. |
What to do next
- Note U0012 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0012
What does U0012 mean?
U0012 means "Medium Speed CAN Communication Bus (+) Open". U0012 reports an interruption of CAN-High, the (+) wire of the medium-speed CAN. It is a generic code, so it means the same on every make.
Is it safe to drive with U0012?
U0012 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0012 fail an emissions test?
U0012 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0012 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U0012 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.