U0015

Code

Generic U — Network/User

Medium Speed CAN Communication Bus (-) Open

Brand: Generic

Type: U — Network/User

Views: UK: 27 EN: 46 RU: 34

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MIL (check engine light) or communication related warning lamp illuminated
Loss of functions controlled by modules on the medium-speed CAN network (e.g., body modules, gateways, sensors)
Intermittent or permanent module communication faults on scan tool
Multiple U‑codes or dependent DTCs for modules that cannot be reached
No data or timeout when requesting data from modules on the MS CAN network

Scan for all U‑codes and module-specific COMM codes; note modules reporting loss of communication
Visually inspect CAN wiring, connectors, and harness routing for damage, corrosion, abrasions, or rodents
Verify relevant fuses and power/ground for modules on this CAN network
Check connector seating at gateway/module junctions and any splice boxes
Measure resistance across CAN H and CAN L at key connector points (expected ~60 Ω with network intact)
Use a multimeter or oscilloscope to measure idle voltages on CAN- and CAN+ at multiple nodes

Recessive state: CAN+ ≈ 2.5 V, CAN- ≈ 2.5 V (both lines near mid‑rail)
Dominant state: CAN+ ≈ 3.5 V, CAN- ≈ 1.5 V (differential ~2.0 V)
Bus differential (dominant) ≈ 2.0 V
Termination resistance: ≈ 60 Ω measured across CAN H and CAN L with network connected (two 120 Ω terminators in parallel)
Typical medium-speed CAN baud rate: commonly 125 kbps (verify vehicle-specific rate)

Connect a diagnostic scan tool; record U0015 and related codes and freeze frame data. Check for multiple network faults.
Identify all modules on the medium-speed CAN network and note their connector/power/ground locations from wiring information.
Visually inspect wiring, connectors, harnesses, and splice points for damage, corrosion, pin push‑out or moisture at each module and gateway.
Verify fuses and module power/grounds. Repair any lost power or poor ground before further testing.
With ignition on, measure idle voltages at CAN+ and CAN- at a convenient connector near the gateway and at remote modules; compare to expected values.
Measure DC resistance across CAN H and CAN L at several points. If resistance is very high or open, suspect an open circuit; if low to ground or battery, suspect short.
Use a scope to view waveforms at multiple nodes while bus is active. Look for missing transitions on CAN-, missing dominant pulses, or flatline on CAN-.
If short/open not localized, disconnect modules one at a time (unplug) while monitoring bus resistance/voltages to identify module causing open or loading the line.
Repair or replace damaged wiring, connectors, or terminals. Replace faulty module transceivers only after isolating the bad module. Ensure proper reconnection and corrosion protection.
Reinstall proper termination resistors if missing or incorrect. Clear codes, perform key-on and test drive, and verify code does not return and all modules communicate normally.