U0001 to U0029 and U0073: CAN network faults

One of the car's CAN networks (high, medium or low speed) has an electrical fault, poor performance, or a module that has stopped talking on it (bus off).

SeverityHighCarrying on can cause expensive damage, so deal with it now.

Can you keep driving?Only as far as the workshop

What does U0001 mean?

CAN is the two-wire network that carries messages between the car's modules. Each network has a positive and a negative line, and the modules watch both. These codes describe the network itself: a line that is open, shorted to ground or to power, or shorted to its partner, or a module that has shut its own connection after too many errors. One fault on a network can disturb every module on it at once.

What causes U0001?

A damaged or chafed network wire, often in a door or where the harness flexes
A corroded connector, especially after water got in
A faulty module dragging the whole network down
A weak battery or poor ground causing errors on several modules
An aftermarket accessory spliced into the network

What to check first for U0001

Check the battery and grounds first: voltage problems cause network codes
Have the network scanned to see which modules answer and which do not
Look for water in footwells and under seats, where connectors often sit
Remove any aftermarket device tapped into the wiring and see whether the fault clears

Can you drive with U0001?

Drive only if the car behaves normally, and only to a workshop. A network fault can switch off safety systems such as the ABS or the airbags, and several warning lights at once mean you should have the car towed.

Since May 2018 an engine warning light that stays on is a major defect at the MOT, so the car fails until the fault is fixed.

Codes on this page

U0001High Speed CAN Communication Bus
U0002High Speed CAN Communication Bus Performance
U0003High Speed CAN Communication Bus (+) Open
U0004High Speed CAN Communication Bus (+) Low
U0005High Speed CAN Communication Bus (+) High
U0006High Speed CAN Communication Bus (-) Open
U0007High Speed CAN Communication Bus (-) Low
U0008High Speed CAN Communication Bus (-) High
U0009High Speed CAN Communication Bus (-) shorted to Bus (+)
U0010Medium Speed CAN Communication Bus
U0011Medium Speed CAN Communication Bus Performance
U0012Medium Speed CAN Communication Bus (+) Open
U0013Medium Speed CAN Communication Bus (+) Low
U0014Medium Speed CAN Communication Bus (+) High
U0015Medium Speed CAN Communication Bus (-) Open
U0016Medium Speed CAN Communication Bus (-) Low
U0017Medium Speed CAN Communication Bus (-) High
U0018Medium Speed CAN Communication Bus (-) shorted to Bus (+)
U0019Low Speed CAN Communication Bus
U0020Low Speed CAN Communication Bus Performance
U0021Low Speed CAN Communication Bus (+) Open
U0022Low Speed CAN Communication Bus (+) Low
U0023Low Speed CAN Communication Bus (+) High
U0024Low Speed CAN Communication Bus (-) Open
U0025Low Speed CAN Communication Bus (-) Low
U0026Low Speed CAN Communication Bus (-) High
U0027Low Speed CAN Communication Bus (-) shorted to Bus (+)
U0028Vehicle Communication Bus A
U0029Vehicle Communication Bus A Performance
U0073Control Module Communication Bus Off

U0100 and U0101lost communication with the engine or transmission module P0560 to P0563system voltage P0600 to P0607engine control module internal faults

Checked on 1 November 2026 · Rafael Soares

These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.