Network, generic

U0018 Medium Speed CAN Communication Bus (-) Shorted to Bus (+)

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modeNo

U0018 describes the two medium-speed CAN lines, CAN-Low and CAN-High, shorted together. With no voltage difference left, receivers see only recessive bits, nobody can win arbitration, and the controllers on the segment eventually go bus-off; onsemi's measurements on the comparable high-speed layer show transmission stopping completely. NXP notes that transceiver diagnosis does not catch this short, so it is inferred from protocol errors. No manufacturer documents U0018 publicly. Expect the complete comfort network to fail together while the powertrain bus stays unaffected. With the battery disconnected, a near-zero resistance between (+) and (-) in place of the normal termination value confirms it; separating connectors section by section narrows the location, often a crushed or wet harness.

Likely causes

Medium-speed bus pair crushed so both wires touch

Water in a connector bridging (+) and (-)

Failed transceiver shorting both bus pins in a comfort module

Symptoms

Entire comfort network fails, powertrain unaffected
Body modules unreachable with the scan tool

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€50–800

Time1–5 h

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

Parts involved

can high wirecan low wire

Related codes

U0009 U0010 U0012 U0015

References: onsemi.com, nxp.com, saabwisonline.com.