U0024: Low Speed CAN Communication Bus (-) Open
What to do
Everything probably works. As at U0021, that is expected rather than reassuring — this network runs on one wire when the other fails, so the car has quietly switched over and carried on.
One thing is worth asking for specifically when the break is found, and it matters more here than on other networks.
The two wires are twisted together and run side by side, so whatever damaged one of them — a crush, a chafe, a rodent, a repair — was touching the other as well.
And the other wire is now the only one you have. A conductor that is nearly severed in the same damaged section is not a future problem; it is the thing that will stop the network.
So ask for the second wire to be inspected along the same stretch, and for a damaged length of loom to be replaced rather than one wire spliced. That is the difference between one visit and two.
Do U0021's free check first: open and close each door and the tailgate slowly and see whether anything changes.
What this code means
The negative line of the low speed data bus is open circuit. Everything at U0021 applies — the single-wire fallback that hides the fault, and the argument for fixing one broken conductor while the vehicle still works rather than two after it stops.
One thing belongs here and follows U0006: the partner conductor is in the same loom and was in contact with whatever broke this one.
On a fault-tolerant network that matters more than it does elsewhere, because the surviving wire is now the only one there is. A conductor that is nearly through, in the same crushed or chafed section, is not a future problem — it is the thing that will take the network down.
So where a break is found, the repair should replace the damaged section of loom rather than splice the one conductor. Inspecting the survivor along the same length is the minimum, and it is the difference between one visit and two.
Likely causes
Start here
- Broken wire in the door harness boot · moderate
- Damaged data bus wiring · moderate
- Damaged wiring harness · moderate
- Corroded or loose connector · easy
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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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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