U0066: Vehicle Communication Bus E (+) Open
What to do
Expect a group of systems to have stopped working together. One broken wire does this — see U0003.
One thing worth mentioning, because it may close an old question.
Has this car had electrical oddities in the past that nobody could reproduce? A dashboard that lit up and cleared, something that failed once and never again.
If so, this is very probably the explanation. A wire down to its last strand or two makes contact most of the time and lets go over a bump — so the same break causes months of unexplained faults before it finally goes open circuit for good.
Saying so is worth more than it sounds: it tells the garage this is likely an old fault rather than a new one, and it means you can stop expecting the ghosts to come back once it is repaired.
When the break is found, ask for the second wire to be inspected along the same stretch. They run twisted together, so whatever damaged one was touching the other.
What this code means
The positive line of vehicle communication bus E is open circuit. See U0003 for what an open does to a differential pair, U0030 for the procedure on a lettered bus, and U0039 for why where the break falls decides what a resistance reading shows.
One note follows from U0064: an open circuit that is currently present is the easy version of this network's problem.
The hard version is the same break, intermittent — a conductor down to a strand or two, making contact until the vehicle hits a bump. So a break found and repaired today may be the second half of a story whose first half was a scatter of unexplained codes months earlier.
Which is worth checking rather than assuming. If the vehicle has a history of intermittent electrical faults nobody could reproduce, this repair very probably explains them — and confirming that is more useful than it sounds, because it closes an open question rather than leaving the owner expecting the ghosts to return.
Likely causes
Start here
- Damaged data bus wiring · moderate
- Corroded or loose connector · easy
- Intermittent wiring fault · moderate
- Damaged wiring harness · moderate
Less common
- Failed bus terminating resistor · specialist
- Water ingress into connector · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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