U0048: Vehicle Communication Bus C (+) Open
What to do
Expect a group of systems to have stopped working together — most likely entertainment, navigation and phone functions. The car will usually drive normally.
One thing here is quietly useful. U0046 explains that a network identified only by a letter might be a pair of wires or might be optical fibre, and that the tests are completely different.
This code answers that question. It describes a wire, a polarity and a break — so this network is a pair of wires, and the ordinary electrical tests apply.
So: one broken wire stops the whole network, because the two wires carry the same message in opposite directions and the computers read the difference. Do not let computers be replaced on the strength of the fault list — they are almost certainly all fine.
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.
Mention any stereo or accessory installation, accident repair, or signs of rodents.
What this code means
The positive line of vehicle communication bus C is open circuit. See U0003 for what an open does to a differential pair and U0030 for the procedure on a lettered bus.
One thing is worth stating once for this whole group of variants, and it resolves the question U0046 raises.
These seven codes describe conductors, polarity and shorts — which only exist on a copper network. So the presence of this code in the fault memory is itself evidence that this bus is a twisted pair rather than an optical ring, whatever the letter suggests.
That is a genuinely useful shortcut: a bare U0046 leaves the medium open, and a U0048 settles it. The electrical tests at U0003 apply, subject to obtaining this network's own resistance figure rather than the high speed CAN one.
Where the break is follows the general list — connectors and splices, flexing harness sections, rodent damage, loom cut and rejoined during repair — and U0006's instruction to inspect the partner conductor wherever a break is found.
Likely causes
Start here
- Damaged data bus wiring · moderate
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
- Poor wiring splice in an aftermarket installation · moderate
Less common
- Failed bus terminating resistor · specialist
- 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
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