Network, generic

U0025 Low Speed CAN Communication Bus (-) Low

Check engine lightUsually off

EmissionsNot relevant

Drive cycleNot required

Limp modeNo

U0025 flags CAN-Low pulled toward ground on a low-speed CAN with two conductors. In the fault-tolerant physical layer of ISO 11898-3 CAN-Low idles near 5 V, so a ground short forces it into its dominant state for good. NXP's TJA1055 (failure 4) first sees a permanently dominant receive signal; after about 0.3 to 1.6 ms it switches the CAN-Low driver off, changes that line's termination to a weak pull-up and continues in single-wire mode on CAN-High. Messages keep flowing, but with weaker immunity to interference, so sporadic dropouts of comfort functions are possible. The transceiver goes back to differential mode by itself once the short is gone. No manufacturer documents U0025 publicly; GM's one-conductor bus has no (-) side at all. Resistance from CAN-Low to ground near 0 Ω with the battery off confirms the fault.

Likely causes

CAN-Low insulation damaged and touching body ground

Harness trapped by a panel, bracket or seat mechanism

Module transceiver internally shorting CAN-Low to ground

Symptoms

Comfort functions work but drop out now and then
Body modules store the code repeatedly

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

U0007 U0019 U0022 U0024 U0026

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