U0003 code meaning
High Speed CAN Communication Bus (+) Open
What U0003 means
U0003 reports a break in the (+) wire of the high-speed CAN, which GM and FCA also call CAN-High. At rest this line idles near 2.5 V and is lifted about one volt for each dominant bit. Once it is cut, modules on the far side of the break lose the differential pair and drop out, while nodes on the intact section may keep talking. Standard high-speed transceivers cannot report a wire interruption on their own, as NXP points out, so whether a module stores U0003 depends on its own monitoring. Harley-Davidson lists U0003 together with U0001 as history codes in the ABS unit of 2017 Touring models when the TechLink interface was plugged in with the ignition already on; there no repair is due. Genuine breaks come from chafing, pushed-back terminals or corrosion.
U0003 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0003
- Modules beyond the break no longer reachable
- Several warnings and fallback modes at once
- Fault appears or disappears when the harness is moved
Common causes of U0003
- Most likelyCAN-High conductor broken at a flex point or after a repair
- PossibleCAN-High terminal pushed back or corroded in a connector
- Less likelyDiagnostic interface connected with ignition on (history code only)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
CAN high wireModule connectorCAN transceiver
What each part of U0003 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 03 | The exact fault in that area. |
What to do next
- Note U0003 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 U0003
What does U0003 mean?
U0003 means "High Speed CAN Communication Bus (+) Open". U0003 reports a break in the (+) wire of the high-speed CAN, which GM and FCA also call CAN-High. It is a generic code, so it means the same on every make.
Is it safe to drive with U0003?
Drive gently and only to a workshop. With U0003 the car can go into limp mode (reduced power) to protect itself.
Will U0003 fail an emissions test?
U0003 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 U0003 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will U0003 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.