Network, generic

U0026 Low Speed CAN Communication Bus (-) High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U0026 means CAN-Low, the (-) line of a two-wire low-speed CAN, is held too high. Since this wire already sits near 5 V at rest in an ISO 11898-3 network, the outcome depends on where the short goes. Against the 5 V supply (failure 6a in NXP's TJA1055) the transceiver stays in differential mode with normal drivers and termination. Against battery voltage (failure 6) its comparator trips after roughly 0.3 to 1.6 ms, the CAN-Low driver is switched off, the termination becomes a weak pull-up and reception continues over CAN-High alone. Either way the bus normally survives, which is why the code is often found without a clear complaint. No manufacturer documents U0026 publicly, and the GM low-speed GMLAN gets by with one conductor. Look for chafing against a feed wire or water in a connector.

Likely causes

CAN-Low chafed against a battery or ignition feed
Moisture in a connector linking CAN-Low to a supply pin
Faulty transceiver driving CAN-Low to its supply

Symptoms

  • Often no noticeable effect
  • Occasional comfort function dropouts when the bus runs on one wire

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–600
Time0.5–4 h

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

Parts involved

low speed can wiringcan low wire

Related codes

U0008U0019U0023U0024U0025

References: nxp.com, law.cornell.edu, saabwisonline.com.