U0007: High Speed CAN Communication Bus (-) Low
Do not keep driving
The car will probably not start, and the dashboard may be full of warnings. That is one damaged wire rather than a dozen failed computers.
The second of the two wires carrying your car's internal network is being held down by a short to the bodywork, so messages cannot get through.
Everything at U0004 applies. Has anything been fitted to the car — a tracker, dashcam, alarm, stereo, tow bar? An earth connection added beside the network wires, or a screw through the loom, causes a lot of these, and unplugging the device to re-test is far quicker than stripping a dashboard.
And did the fault come and go before becoming permanent? That is typical of a wire rubbing through against bodywork, and it tells a technician to move the loom by hand rather than reach for a meter.
The car will need recovering.
What this code means
The negative line of the high speed data bus is being held low. See U0003 for the pair and the resistance test, and U0004 for the short-to-earth argument, which applies here unchanged.
The voltage signature is the mirror image and it is worth stating precisely, because it is what distinguishes this from a healthy bus at rest.
Both wires idle at about 2.5 volts, and during a message CAN-L falls to roughly 1.5 while CAN-H rises to roughly 3.5. So a CAN-L line sitting at zero has been pulled to earth, and the pair can no longer produce the difference a receiver needs.
Which produces a measurement trap worth knowing. A bus with no traffic on it also sits still — both wires at 2.5 volts, doing nothing. The two look similar on a cheap meter and are entirely different faults: one wire at zero is a short, both wires at 2.5 is silence. Reading each wire against earth separately, rather than reading the pair, tells them apart in seconds.
Otherwise this is U0004's fault on the other conductor, with the same causes in the same order — a chafe against the body, an aftermarket earth taken beside the pair, water in a connector — and the same instruction: move the loom by hand before reaching for a meter.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Damaged data bus wiring · moderate
- Poor wiring splice in an aftermarket installation · moderate
- Damaged wiring harness · moderate
Less common
- Water ingress into connector · moderate
- Another module holding the bus down · specialist
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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