Fault Family System: Network (U-Codes) 9 SAE Codes

LS CAN Bus Fault

Diagnostic & Technical Explanation

U0019 points to a fault on the low-speed, fault-tolerant CAN segment (roughly 33 kbps single-wire or dual-wire GMLAN-style network) that links lower-priority body accessories. This bus is intentionally designed to keep running in a degraded single-wire mode if one conductor fails, so total loss of communication usually means both wires are compromised, a shared ground is lost, or a bus-bias voltage regulator inside a module has failed -- a different wiring picture from the terminated high-speed backbone. Because there is no strict 120-ohm termination requirement here, a bias-voltage check is more diagnostic than a resistance check.

These 9 diagnostic trouble codes share one detection mechanism and one repair path, which is why MechanicDB groups them into a single authored fault family rather than repeating the same explanation 9 times.

Codes in this family (9)

Code	Definition	Repair coverage
U0019	Low Speed CAN Communication Bus	4 ranked fixes
U0020	Low Speed CAN Communication Bus Performance	4 ranked fixes
U0021	Low Speed CAN Communication Bus (+) Open	4 ranked fixes
U0022	Low Speed CAN Communication Bus (+) Low	4 ranked fixes
U0023	Low Speed CAN Communication Bus (+) High	4 ranked fixes
U0024	Low Speed CAN Communication Bus (-) Open	4 ranked fixes
U0025	Low Speed CAN Communication Bus (-) Low	4 ranked fixes
U0026	Low Speed CAN Communication Bus (-) High	4 ranked fixes
U0027	Low Speed CAN Communication Bus (-) shorted to Bus (+)	4 ranked fixes

What this page does not show

This page publishes the fault mechanism and the code index. The licensed dataset adds, for every one of the 15,886 codes, the full authored repair set (56,729 procedures in total) with the fields deliberately withheld here:

Procedures 2..n after the first-listed procedure
Aftermarket parts cost ranges in USD (est_parts_cost_min/max_usd)
Professional labor-hour estimates (est_labor_hours)
Step-by-step diagnostic and repair instructions
Replacement-part mappings and catalog lookups
6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)

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