U0280

Code

Generic U — Network/User

CAN Bus Communication Fault

Brand: Generic

Type: U — Network/User

Views: UK: 15 EN: 39 RU: 19

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open, shorted or high-resistance CAN_H or CAN_L wiring
Corroded or loose connectors or grounding points on the network
Missing or incorrect termination (open or extra terminators)
Failed or intermittent control module on the CAN network
Low battery or poor battery/charging system voltage during communication
Aftermarket electrical accessories or wiring faults loading the bus

Symptoms

One or more modules non-responsive or missing from scan tool network list
Multiple communication-related DTCs set
Loss of functions controlled over CAN (e.g., instrument cluster, ABS, HVAC)
Intermittent or permanent MIL/check engine illumination
Gauges, display or warning lights frozen or showing incorrect info
No-crank/no-start if powertrain module communication is lost

What to check

Connect a scan tool and list all modules detected on each CAN network; note related U0xxx/U1xxx codes
Inspect connectors, pins and wiring for physical damage, corrosion or moisture
Check vehicle battery voltage and charging system; verify stable supply during tests
Measure DC resistance across CAN_H and CAN_L (expect ~60 ohms for proper termination with ignition off)
Measure idle voltages: CAN_H and CAN_L at a known good connector
Use a scope or CAN bus analyzer to view waveform integrity and bus bit-rate

Signal parameters

Recessive (idle) voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (values vary slightly by manufacturer)
Dominant state: CAN_H ~3.5 V, CAN_L ~1.5 V (differential ≈ 2 V)
Expected resistance across CAN_H and CAN_L with ignition off ≈ 60 ohms (two 120 Ω terminators in parallel)
Common CAN bus speeds: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific bitrate with scan tool)
Healthy waveform: clean differential edges, correct bit timing, limited noise, no bus contention

Diagnostic algorithm

Read all DTCs and freeze frame data; record which modules are missing or throwing communication faults.
Verify battery state-of-charge and charging system operation. Recharge or support battery if voltage low during tests.
Visually inspect CAN wiring, module connectors, and ground points near affected modules and at the gateway/ECU.
With ignition off, measure resistance between CAN_H and CAN_L at a central access connector; confirm ~60 Ω.
With key on, measure DC voltages of CAN_H and CAN_L at the same point; compare to expected recessive voltages.
If voltages/resistance are out of range, trace and repair wiring, connectors, or grounds found damaged or corroded.
If basic checks pass, use an oscilloscope or CAN analyzer to capture waveforms while reproducing the fault; look for collisions, missing nodes, or noise.
Isolate the faulty node by disconnecting modules one at a time (follow OEM safety and procedure). If disconnecting a module clears the fault, suspect that module or its harness.
Replace or repair the identified wiring, connector, or module as required. Ensure correct termination and no extra devices loading the bus.
Clear codes and perform a full network scan; road-test or stress-test to confirm the U0280 does not return.

Likely causes

Damaged or disconnected wiring or connector at a recently-serviced component
Loose or corroded ground or power connections to a module
Failed CAN transceiver in one module causing bus contention
Incorrect termination resistor value or open termination
Intermittent fault caused by vibration or temperature (loose connector)

Fault status

⚠️ Status

U0280 - CAN Bus Communication Fault: vehicle network communication interrupted or corrupted. One or more modules not responding or messages missing; inspect CAN wiring, terminations, connectors, power/ground and module transceivers.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours