U0005: High Speed CAN Communication Bus (+) High
Do not keep driving
This is the one fault in this family that can damage things rather than just stopping them, so it is worth understanding before repairs are discussed.
The wires carrying your car's internal network are designed for a signal of two or three volts. This fault means full battery voltage has got onto one of them — and every computer on the network is connected to that same wire.
So be prepared for the repair to have two stages. The damaged wire gets found and fixed, and the car may still not work, because one or more computers were damaged while the voltage was present. A garage that repairs the wiring and then reports further faults is not moving the goalposts — that is what this particular fault does.
Two questions will very likely find the cause, and both are yours to answer.
Has anything been fitted to the car? An alarm, tracker, dashcam, light bar, tow bar, insurance box or stereo. A live feed tapped next to the network wires, or a self-stripping connector clipped onto the wrong wire, causes most of these.
And has the battery ever been connected the wrong way round, or jump-started backwards? That puts battery voltage where it does not belong right across the car, and people remember it but rarely mention it. Say so if it happened; it saves a great deal of searching.
The car will need recovering.
What this code means
The positive line of the high speed data bus is being held high. See U0003 for the pair and the resistance test, and U0004 for the voltage signature that identifies these.
This is the damaging one, and that is what separates it from the rest of the family.
The other faults in this range stop the network. This one can destroy it. Every module on the bus connects through a transceiver designed for a signal that swings between roughly 1.5 and 3.5 volts. Battery voltage on a bus wire is well outside anything those parts are built to survive, and it is applied to all of them at once, because they are all on the same pair.
So the consequence worth stating before any repair is discussed: a vehicle whose bus has been shorted to power may need more than a wiring repair. Modules can be damaged, and they are damaged silently — the wire gets found and fixed, the vehicle still does not work, and the second stage of the diagnosis begins from a much worse position. A workshop that repairs the short and then reports further faults is not moving the goalposts; that is what this fault does.
Where it comes from is almost always something added. A live feed tapped beside the bus pair, a screw through a loom carrying both, a self-stripping connector clipped onto the wrong wire, or an installation that used the bus wires believing them to be something else. Aftermarket alarms, trackers, dashcams, light bars, tow bar looms and audio installations account for the great majority.
And two events that are not installations: a jump start with reversed polarity, and a battery connected backwards. Either can put battery voltage where it does not belong across the whole vehicle, and a bus code afterwards is one symptom among several.
So the first question is what was fitted or done recently, and the second is whether the vehicle has ever had its battery connected the wrong way round — which owners remember and rarely volunteer.
Likely causes
Start here
- Wiring shorted to voltage · moderate
- Poor wiring splice in an aftermarket installation · moderate
- Faulty aftermarket alarm or immobiliser installation · moderate
- Damaged data bus wiring · moderate
Less common
- Damaged wiring harness · moderate
- Water ingress into connector · 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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