Network, generic

U0008 High Speed CAN Communication Bus (-) High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U0008 means CAN-Low, the (-) wire of the high-speed CAN, is forced too high, typically through contact with the 12 V system or another supply rail. This fault blocks the bus: CAN-Low can no longer be driven down, no dominant state develops, and both onsemi and NXP found that transmission becomes impossible. Senders accumulate errors until they reach bus-off, so U0001 and lost-communication codes nearly always appear alongside, and engine, transmission or brake electronics may switch to stored default values. No manufacturer documents U0008 publicly. With ignition on, CAN-Low reading close to battery voltage instead of about 1.5 to 2.5 V confirms it; the contact point is usually where the bus pair runs beside a supply feed, for example after an accessory installation.

Likely causes

CAN-Low chafed against a battery or ignition supply wire
Retrofit wiring tapped into the bus pair by mistake
Bent pin or moisture linking CAN-Low to a supply contact

Symptoms

  • Total communication loss on the high-speed network
  • Many warning lamps, possible no-start
  • Scan tool cannot reach powertrain modules

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,000
Time1–6 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

can low wiremodule connector

Related codes

U0001U0005U0006U0007

References: onsemi.com, nxp.com, ti.com.