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U0005High Speed CAN Communication Bus (+) High

The CAN High (+) wire of the high-speed CAN bus is stuck at high voltage, typically from a short to battery power.

Definition

The PCM and other modules monitor bus line voltages; when CAN High is pulled up near battery voltage instead of idling around 2.5 V, dominant/recessive bits can no longer be formed and communication fails on that segment. U0005 sets along with lost-communication codes from the modules that dropped offline. A sustained short to 12 V can also damage CAN transceivers in connected modules, so expect multiple warning lamps, dead gauges, limp mode, or a no-start until repaired.

Common causes

  • CAN High wire chafed against a battery-voltage feed in the harness
  • Melted or water-contaminated connector bridging CAN High to a power pin
  • Failed CAN transceiver inside a module pulling the line to its supply rail
  • Harness damage from collision or engine-compartment heat
  • Miswired aftermarket installation feeding 12 V onto the bus

Common misdiagnoses

  • Control modules replaced before locating the harness short to power
  • PCM replacement based on the volume of network codes
  • Battery or charging repairs for symptoms caused by the dead bus
  • DLC/gateway replacement without voltage testing

Troubleshooting steps

  1. 1.Measure CAN High voltage at the DLC

    Key on, pin 6 to ground: a steady reading near battery voltage (about 12 V) instead of about 2.6 V confirms a short to power.

  2. 2.Determine if the short is switched or constant

    Check the voltage key-off as well; a constant 12 V points to an unswitched battery feed, narrowing which circuits could be contacting the bus.

  3. 3.Isolate modules one at a time

    Disconnect each module on the bus while monitoring pin 6 voltage; if the voltage drops to normal, the disconnected module's transceiver has failed internally.

  4. 4.Split the bus to find the harness segment

    Open junction connectors to divide the network and identify which physical section holds the wire-to-wire short.

  5. 5.Inspect for chafe against power circuits

    Follow the isolated segment looking for melted insulation or rub-throughs where the bus runs alongside battery feeds; repair and reroute.

  6. 6.Verify no modules were damaged

    After repair, rescan the network; any module still offline with good power, ground, and bus wiring likely has a burned transceiver and needs replacement.

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