U0006: High Speed CAN Communication Bus (-) Open
Do not keep driving
The car will probably not start, and everything on the dashboard may be complaining at once. That is one broken wire.
Everything at U0003 applies: the two network wires are not a main and a spare — they carry the same message twice and the computers read the difference, so breaking either one stops the lot. Ask for the free resistance check across pins 6 and 14 of the diagnostic socket, which reads about 60 ohms on a healthy car and about 120 when the wiring is broken.
One thing worth asking for specifically when the break is found. The two wires are twisted together and run side by side for their whole length, so whatever damaged one of them — a crush, a chafe, a rodent, a repair — was touching the other as well.
Ask for the partner wire to be inspected along the same stretch, not just the broken one. A conductor that is nearly severed will finish the job a few thousand miles later, and that second visit costs as much as the first.
The car will need recovering rather than driving. Do not let computers be replaced on the strength of the long fault list — they are almost certainly all fine.
What this code means
The negative line of the high speed data bus is open circuit. Everything at U0003 applies unchanged — the pair, the resistance test at the diagnostic socket, and why one broken wire stops the whole network.
One thing is worth adding here rather than there, because it changes how the repair should be done.
The two wires are twisted together and run in the same loom for their whole length. So whatever broke one of them was almost certainly in contact with the other — a crush, a chafe point, a rodent, a cut during accident repair, a connector full of water.
Which means finding and repairing one break is not the end of the job. The partner wire in the same section should be inspected along the same length, because a conductor that is nearly through will complete the failure a few thousand miles later, and the second visit costs as much as the first.
And where a section of loom is damaged rather than a single conductor, the honest repair is to replace that section rather than to splice one wire. A bus pair with a repair in one conductor and not the other is no longer a matched pair, and the small differences that introduces are exactly what the twisting exists to prevent.
Likely causes
Start here
- Damaged data bus wiring · moderate
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
- Failed bus terminating resistor · specialist
Less common
- Water ingress into connector · moderate
- Poor wiring splice in an aftermarket installation · 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
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