U0064 Moderate Generic / SAE

U0064: Vehicle Communication Bus E

Network and Communication Bus Signal and Bus Off Emissions related

What to do

If the fault comes and goes — a dashboard that lights up and then clears, a car that misbehaves once a week — read this. It is the hardest kind to find, and you can help more than any test.

A network interruption lasting a fraction of a second is enough to make every computer in the car report that it cannot hear the others. The network then recovers. So the fault list looks like a catastrophe and describes a moment, and the car is working perfectly by the time anyone looks at it.

Two things are worth asking for, and both cost nothing.

Ask them to read the codes before clearing anything. The car records when each fault was stored and what the battery voltage was at the time — and codes stored in the same trip are one event rather than fifteen problems. Clearing the codes destroys all of it.

And write down what you notice. Does it happen on cold mornings? Only once warm? On rough roads? After the car has stood? Those are three different answers pointing at three different causes, and they are the one thing a garage cannot work out for itself.

Be aware that this is genuinely one of the most expensive faults to chase, so what you can tell them is worth more than an hour of their time.

What this code means

A fault has been detected on vehicle communication bus E. See U0028 for why the letter must be resolved first and U0003 for the electrical faults.

This page carries the argument for the version of a bus fault that is present when nobody is looking, because it is the one that costs the most and it needs a method rather than a test.

A bus interruption lasting a fraction of a second is enough. Every module that was expecting a message and did not receive one stores a lost-communication code, and the network then recovers — so the fault memory afterwards records a catastrophe and describes a moment.

Which produces the picture that sends diagnoses wrong: fifteen codes naming a dozen modules, on a vehicle that is currently working perfectly.

The method that resolves it is not measurement. It is correlation, and the data is already in the vehicle.

Modules record when a fault was stored — an ignition cycle count, an odometer reading, sometimes a timestamp. Codes carrying the same value are one event. Fifteen codes from a single cycle are one interruption; fifteen spread across fifteen cycles are a recurring one, and the two need different work.
The stored conditions matter as much as the code. A bus fault consistently logged at low system voltage is a battery or charging problem rather than a wiring one — transceivers misbehave as voltage falls, which is why U0100 lists it.
And all of it is destroyed by clearing the codes, which is why reading before resetting is not fastidiousness.

The physical test that finds what remains is movement and temperature rather than a meter. Flex the loom by hand along its accessible length while the network's error counters are watched, and note whether the fault follows cold mornings, warm running, or rough roads — three different answers pointing at three different things.

And the honest closing point: an intermittent bus fault is among the most expensive things on a vehicle to chase. What the owner noticed is genuinely worth more than an hour of workshop time, and it is the one input a workshop cannot generate for itself.

Likely causes

Start here

Less common

Poor wiring splice in an aftermarket installation · moderate
Water ingress into connector · moderate

Symptoms

Components involved

Information, not instruction

CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.

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.