U1330

Code

Generic U — Network/User

Lost Communication With CAN Network Module

Brand: Generic

Type: U — Network/User

Views: UK: 10 EN: 12 RU: 10

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Page language: EN

Causes

Open or short in CAN high/low wiring
Failed or intermittent module (node) on the CAN bus
Missing or incorrect termination resistor(s)
Power or ground fault to one or more modules
Bus voltage levels out of tolerance (battery low, charging issue)
Incorrect baud rate or module configuration after replacement or reflash

Symptoms

Diagnostic trouble code U1330 stored
One or more modules missing from the network when scanned
Intermittent or permanent loss of functionality related to the missing module
Multiple CAN-related codes present or cascading faults
Possible instrument cluster warnings or limp-home behavior
No communication on the specific CAN network using a scan tool

What to check

Use a capable scan tool to confirm U1330, view network topology and modules present/absent, and capture freeze-frame/data
Visually inspect connectors, pins, and harness for damage, corrosion or pin push-out
Verify battery voltage and chassis/body/engine grounds are clean and tight
Measure DC resistance between CAN_H and CAN_L with ignition off (expected ~60 Ω for a normally terminated network; may vary with multiple nodes)
Backprobe CAN_H and CAN_L at suspected module connector and measure voltages with ignition ON and key off states
Wiggle harnesses and connectors while monitoring the bus and scan-tool communication for intermittent changes

Signal parameters

Idle (recessive) CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V
Dominant state typically: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Differential voltage (CAN_H - CAN_L): 0 V (recessive) to ~2 V (dominant)
Expected DC resistance across CAN_H and CAN_L (with key off): ~60 Ω for properly terminated bus (two 120 Ω in parallel or equivalent)
Common bus baud rates: 125 kb/s, 250 kb/s, 500 kb/s (verify vehicle-specific rate before replacing modules)

Diagnostic algorithm

Confirm code and network: Use a scan tool to verify U1330, identify which CAN network and which module is reported missing or timed out.
Check power/ground: Verify battery voltage and measure primary power and ground at the affected module connector(s). Repair any poor grounds or low supply issues.
Visual inspection: Inspect wiring, connectors, splices, and grounds for corrosion, damage, or rodent/abrasion damage. Repair as needed.
Confirm module presence: Scan other modules on the same CAN network to determine if only one node is missing or the entire bus is dead.
Measure termination/resistance: With ignition off and connectors connected, measure resistance between CAN_H and CAN_L (expect ~60 Ω). If open or far off, isolate sections to find missing/failed termination.
Probe live signals: Backprobe CAN_H and CAN_L at module connector with an oscilloscope (preferred) or voltmeter to verify idle voltages and presence of communication frames. Look for correct voltage levels and the expected dominant/recessive transitions.
Isolate nodes: If a short or fault is suspected, disconnect suspect modules one at a time (or disconnect harness sections) and re-check the bus to see if communication returns. This helps locate a shorted node.
Repair wiring/connectors: Repair any damaged wiring, shorts, or poor connections. Replace corroded connectors/pins and secure grounds.
Reflash/configure: If module replacement or software mismatch is suspected, verify correct programming/configuration and reflash or reconfigure as required.
Clear codes and retest: After repairs, clear codes, perform a full network scan, and road-test to confirm the fault does not return. Record any intermittent behavior for further investigation.
If problem persists: Escalate to wiring diagrams, module bench testing, or manufacturer service information for advanced diagnostics. Consider replacing the suspected failed module only after isolating the fault to the module.