U0016: Medium Speed CAN Communication Bus (-) Low
What to do
The car will almost certainly drive normally, with a group of electrical fittings not working.
Two free checks, and between them they find a large share of these.
Slide the front seats all the way forward and all the way back, and watch whether anything changes. The wiring that feeds a seat has to survive every slide, recline and fold, thousands of times — and a fault that appears at one end of the runners is a stretched or trapped loom rather than a broken part.
Then look underneath the seats for anything that has been pushed in there and is now pressing on the wiring or a plug. That costs nothing and fixes more of these than it ought to.
And check for water — damp carpets, a wet boot floor, sloshing in a door. On this network water is a leading cause, and finding it is the repair rather than a step towards one.
Check your lights and indicators before driving at night.
What this code means
The negative line of the medium speed data bus is being held low. See U0007 for the voltage signature and U0013 for why water outranks chafing as a cause on this network.
One route belongs specifically here and it is the commonest under-seat fault on any vehicle: the harness that has to reach a seat.
A seat slides through its full travel, reclines, and on many vehicles tips forward and folds flat — and the loom feeding it must survive every one of those movements, thousands of times. It is also the one place in the cabin where things are pushed underneath, vacuumed around, and knelt on.
So the free check is the same shape as the door one at U0012: slide the seat through its full travel and watch whether anything changes. A fault that appears at one end of the runners is a stretched, trapped or partly severed harness, and it is a repair to a loom rather than a module.
And look underneath for anything that has been pushed in there and is now bearing on the loom or its connector — which is free, immediate, and resolves more of these than it should.
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
- Corroded or loose connector · easy
- Poor wiring splice in an aftermarket installation · 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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