U0071 code meaning
Vehicle Communication Bus E (-) High
What U0071 means
With U0071 the (-) conductor of Vehicle Communication Bus E sits too high, mostly by a short to battery voltage. Where Bus E is a high-speed CAN this is CAN-Low, and the bus dies: the line can no longer be pulled down, onsemi's node failed every start of frame, and NXP's TJA1041 note lists CAN-Low at battery or at 5 V as faults that prevent any communication. All Bus E modules drop out, and the gateway or other networks log them as lost. A fault-tolerant low-speed transceiver reacts differently; NXP's TJA1055 detects CAN-Low at battery voltage after a filter delay, turns its CAN-Low output off and receives via CAN-High alone. No manufacturer documents U0071 publicly. With ignition on, a CAN-Low reading at battery level rather than in the 1.5-2.5 V band confirms it.
U0071 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0071
- All functions on Bus E fail together (high-speed type)
- Gateway or other modules report lost communication
Common causes of U0071
- Most likely(-) wire of Bus E chafed against a battery or ignition feed
- PossibleWater in a connector linking the (-) wire to a supply pin
- Less likelyDamaged transceiver driving the (-) line high
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus e wiringCAN transceiver
What each part of U0071 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 71 | The exact fault in that area. |
What to do next
- Note U0071 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 U0071
What does U0071 mean?
U0071 means "Vehicle Communication Bus E (-) High". With U0071 the (-) conductor of Vehicle Communication Bus E sits too high, mostly by a short to battery voltage. It is a generic code, so it means the same on every make.
Is it safe to drive with U0071?
Drive gently and only to a workshop. With U0071 the car can go into limp mode (reduced power) to protect itself.
Will U0071 fail an emissions test?
U0071 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 U0071 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0071 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.