U0030 to U0072: communication buses A to E
One of the car's communication buses, lettered A to E, has a fault on its positive or negative line, poor performance, or its two lines shorted together.
SeverityHighCarrying on can cause expensive damage, so deal with it now.
Can you keep driving?Only as far as the workshopWhat does U0030 mean?
Besides the buses named in U0001 to U0029, the standard reserves five more, A to E, which each maker assigns to its own networks. Each bus has a positive and a negative line carrying the same message in mirror image, so a module can still read it when one line is disturbed. These codes say which line is wrong: open (no connection), low (shorted toward ground), high (shorted toward the supply), or the negative line touching the positive one. Which network a letter means depends on the car, so the maker's wiring diagram tells you where to look.
What causes U0030?
- A bus wire cut or crushed, for example under a seat rail or behind a trim panel
- A pin pushed back or spread in a connector, so it no longer makes contact
- Corrosion in a connector after a leak from a windscreen, a sunroof drain or a door seal
- A module with a failed network chip pulling one line low or high
- A repair splice or an add-on device wired into the bus
What to check first for U0030
- Find out from the maker's information which network the letter means on this car
- With the battery disconnected, measure the resistance between the two lines at the diagnostic socket
- Unplug the modules on that bus one at a time and see whether the fault clears
- Inspect the bus wiring where it passes hinges, seat rails and floor edges
Can you drive with U0030?
Drive only if the car behaves normally, and only to a workshop. Depending on the bus, a fault can take out the instruments, the electronic brake aids or the gearbox control; have the car towed if warning lights come on together or it goes into a protective mode.
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
43
- U0030Vehicle Communication Bus A (+) Open
- U0031Vehicle Communication Bus A (+) Low
- U0032Vehicle Communication Bus A (+) High
- U0033Vehicle Communication Bus A (-) Open
- U0034Vehicle Communication Bus A (-) Low
- U0035Vehicle Communication Bus A (-) High
- U0036Vehicle Communication Bus A (-) shorted to Bus A (+)
- U0037Vehicle Communication Bus B
- U0038Vehicle Communication Bus B Performance
- U0039Vehicle Communication Bus B (+) Open
- U0040Vehicle Communication Bus B (+) Low
- U0041Vehicle Communication Bus B (+) High
- U0042Vehicle Communication Bus B (-) Open
- U0043Vehicle Communication Bus B (-) Low
- U0044Vehicle Communication Bus B (-) High
- U0045Vehicle Communication Bus B (-) shorted to Bus B (+)
- U0046Vehicle Communication Bus C
- U0047Vehicle Communication Bus C Performance
- U0048Vehicle Communication Bus C (+) Open
- U0049Vehicle Communication Bus C (+) Low
- U0050Vehicle Communication Bus C (+) High
- U0051Vehicle Communication Bus C (-) Open
- U0052Vehicle Communication Bus C (-) Low
- U0053Vehicle Communication Bus C (-) High
- U0054Vehicle Communication Bus C (-) shorted to Bus C (+)
- U0055Vehicle Communication Bus D
- U0056Vehicle Communication Bus D Performance
- U0057Vehicle Communication Bus D (+) Open
- U0058Vehicle Communication Bus D (+) Low
- U0059Vehicle Communication Bus D (+) High
- U0060Vehicle Communication Bus D (-) Open
- U0061Vehicle Communication Bus D (-) Low
- U0062Vehicle Communication Bus D (-) High
- U0063Vehicle Communication Bus D (-) shorted to Bus D (+)
- U0064Vehicle Communication Bus E
- U0065Vehicle Communication Bus E Performance
- U0066Vehicle Communication Bus E (+) Open
- U0067Vehicle Communication Bus E (+) Low
- U0068Vehicle Communication Bus E (+) High
- U0069Vehicle Communication Bus E (-) Open
- U0070Vehicle Communication Bus E (-) Low
- U0071Vehicle Communication Bus E (-) High
- U0072Vehicle Communication Bus E (-) shorted to Bus E (+)
Related codes
Checked on · 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.
