U0025 Moderate Generic / SAE

U0025: Low Speed CAN Communication Bus (-) Low

Network and Communication Bus Signal and Bus Off

What to do

Everything may still work, since this network keeps running on one wire when the other fails.

Two free checks are worth doing, and between them they find a good share of these.

Slide the front seats all the way forward and all the way back, and watch whether anything changes. The wiring feeding a seat has to survive every slide, recline and fold, thousands of times — and a fault appearing at one end of the runners is a trapped or stretched loom rather than a broken part.

Then look underneath the seats for anything pushed in there that is now pressing on the wiring or a plug.

And one thing worth saying to the garage: if there is a seat or airbag fault stored as well, mention both together. Two codes coming from the same part of the car are usually one damaged loom, and treating them as separate problems is how a single trapped wire turns into two diagnoses.

Also mention damp carpets, and whether the fault seems to follow the weather.

What this code means

The negative line of the low speed data bus is being held low. See U0007 for the voltage signature, U0022 for why a damp short on this network comes and goes, and U0019 for the fallback that hides it.

One route belongs here and it is the under-seat harness from U0016, for the same reason: this network reaches the seats, and a seat harness has to survive every slide, recline and fold, thousands of times, in the one part of the cabin where things are also pushed underneath.

The free check is the same and it is worth repeating because it costs nothing: slide the seat through its full travel and watch whether anything changes.

And on this network there is a second reason to look there. Seat modules, occupant sensing and seat heating all sit on or near the body networks, so a harness damaged under a seat frequently produces a restraints or seat code alongside this one. Two codes from the same place are one fault, and treating them separately is how a single trapped loom becomes two diagnoses.

Likely causes

Start here

Damaged wiring under the front seats · moderate
Wiring shorted to ground · moderate
Water ingress into connector · moderate
Damaged data bus wiring · moderate

Less common

Intermittent wiring fault · moderate
Corroded or loose connector · easy

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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