Network, generic

U0022 Low Speed CAN Communication Bus (+) Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U0022 indicates a ground short on CAN-High, the positive conductor of a dual-wire low-speed CAN. In the fault-tolerant design of ISO 11898-3, where CAN-High idles at about 0 V and only rises for dominant bits, a ground short simply takes that rise away. NXP's TJA1055 lists CAN-High to ground as failure 5 and keeps transmitting and receiving differentially, since its receiver threshold is chosen so that reception stays correct in this case as well. The network therefore keeps working, and the driver often notices nothing apart from the stored code. On GM's single-wire low-speed GMLAN the (+)/(-) naming does not fit. No manufacturer documents U0022 publicly. With the battery disconnected, a reading near zero ohms from CAN-High to ground confirms the short; trim screws and seat rails are typical culprits.

Likely causes

CAN-High insulation chafed through against body ground
Wire pierced by a trim screw or trapped under a seat rail
Internal transceiver fault pulling CAN-High low

Symptoms

  • Frequently no symptom besides the stored code
  • Rare sporadic comfort function faults

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 high wire

Related codes

U0004U0019U0021U0023U0025

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