What are common causes for U0027?

CAN-Low shorted to battery (high) · Gateway module routing CAN messages incorrectly (low) · CAN terminating resistor (120 Ω) drifted out of spec (low)

What symptoms does U0027 show?

Multiple warning lights may illuminate · Affected modules may go into limp mode or shut down · Specific functions inoperative depending on module · Diagnostic tools may show communication faults

Network generic / SAE

U0027

Low Speed CAN Communication Bus (-) High

CAN-Low on the low-speed bus is shorted to battery. Bus signaling is no longer possible; comfort modules drop offline.

SystemNetwork

Typegeneric / SAE

GroupU0

Range / number– / 27

Possible causes

CAN-Low shorted to battery high
Gateway module routing CAN messages incorrectly low
CAN terminating resistor (120 Ω) drifted out of spec low

Symptoms

Multiple warning lights may illuminate
Affected modules may go into limp mode or shut down
Specific functions inoperative depending on module
Diagnostic tools may show communication faults

Inspection / repair

Difficulty: hard
DIY: shop recommended
Estimated cost: 60–600 €
Estimated time: 0.8–5 h
Component: low speed can wiring
MIL / check engine light

Sources

Wikipedia · CAN bus

References

sae:J2012 iso:11898