U0027 code meaning
Low Speed CAN Communication Bus (-) Shorted to Bus (+)
What U0027 means
U0027 describes the two wires of a low-speed CAN, (+) and (-), touching each other. On a high-speed bus such a short ends all traffic, but the fault-tolerant layer of ISO 11898-3 is built to ride it out. NXP's TJA1055 counts it as failure 7: the receive signal first sticks at dominant, then within about 0.3 to 1.6 ms the transceiver turns off its CAN-Low driver, leaves that wire with only a weak pull-up and carries on in single-wire mode. Comfort functions usually still work, though with less margin against interference, and differential operation resumes by itself once the short is cleared. No manufacturer documents U0027 publicly; a single-wire bus like GM's low-speed GMLAN cannot have this fault at all. Squeezed harness sections and wet splices are the likely spots; compare the high-speed sibling U0009.
U0027 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0027
- Comfort network keeps running, sometimes with dropouts
- Higher sensitivity to electrical interference
- Code stored in several body modules at once
Common causes of U0027
- Most likelyHarness crushed so that both bus wires make contact
- PossibleWater in a splice or connector bridging the two wires
- Less likelyDamaged transceiver bridging its two bus pins
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Low speed CAN wiringCAN high wireCAN low wire
What each part of U0027 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 27 | The exact fault in that area. |
What to do next
- Note U0027 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 U0027
What does U0027 mean?
U0027 means "Low Speed CAN Communication Bus (-) Shorted to Bus (+)". U0027 describes the two wires of a low-speed CAN, (+) and (-), touching each other. It is a generic code, so it means the same on every make.
Is it safe to drive with U0027?
U0027 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0027 fail an emissions test?
U0027 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 U0027 to fix?
Difficulty: medium. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0027 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.