U0025 code meaning
Low Speed CAN Communication Bus (-) Low
What U0025 means
U0025 flags CAN-Low pulled toward ground on a low-speed CAN with two conductors. In the fault-tolerant physical layer of ISO 11898-3 CAN-Low idles near 5 V, so a ground short forces it into its dominant state for good. NXP's TJA1055 (failure 4) first sees a permanently dominant receive signal; after about 0.3 to 1.6 ms it switches the CAN-Low driver off, changes that line's termination to a weak pull-up and continues in single-wire mode on CAN-High. Messages keep flowing, but with weaker immunity to interference, so sporadic dropouts of comfort functions are possible. The transceiver goes back to differential mode by itself once the short is gone. No manufacturer documents U0025 publicly; GM's one-conductor bus has no (-) side at all. Resistance from CAN-Low to ground near 0 Ω with the battery off confirms the fault.
U0025 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 U0025
- Comfort functions work but drop out now and then
- Body modules store the code repeatedly
Common causes of U0025
- Most likelyCAN-Low insulation damaged and touching body ground
- PossibleHarness trapped by a panel, bracket or seat mechanism
- Less likelyModule transceiver internally shorting CAN-Low to ground
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 low wire
What each part of U0025 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 25 | The exact fault in that area. |
What to do next
- Note U0025 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 U0025
What does U0025 mean?
U0025 means "Low Speed CAN Communication Bus (-) Low". U0025 flags CAN-Low pulled toward ground on a low-speed CAN with two conductors. It is a generic code, so it means the same on every make.
Is it safe to drive with U0025?
U0025 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0025 fail an emissions test?
U0025 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 U0025 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U0025 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.