U1003

Code

DS U — Network/User

General CAN fault: Not characterised

Brand: DS

Type: U — Network/User

Views: UK: 2 EN: 8 RU: 3

AI status

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Page language: EN

Causes

Open or shorted CAN wiring (H or L)
Damaged or corroded connector / pin on a CAN node
Failed CAN transceiver in a control module
Missing or incorrect bus termination resistors
Low battery voltage or poor battery/ground connections
Software/configuration mismatch between modules or failed module flash

Symptoms

Illumination of communication warning lamp or MIL (may vary by vehicle)
Loss of functions controlled by modules on affected CAN network (e.g., instrument cluster, HVAC, ADAS)
Intermittent operation of electrical systems
Multiple communication-related fault codes present
Frozen or missing live data parameters on scan tool

What to check

Connect a competent diagnostic scan tool and record all stored and pending U-/P- codes and freeze frame data
Check vehicle battery voltage (key ON) and battery ground connections
Visually inspect CAN connectors, boots and wiring harness for damage, corrosion or water ingress
Check for additional related U-codes that identify a specific module
With key OFF, measure DC resistance between CAN_H and CAN_L at a convenient connector (see signal_params)
With key ON, measure voltage to ground on CAN_H and CAN_L at a known good connector

Signal parameters

With key ON, both CAN_H and CAN_L (recessive) nominally ~2.5 V (allow ±0.3 V)
Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈2.0 V)
Voltage to ground on either line should not be near battery positive or chassis ground when recessive
Line-to-line resistance with ignition OFF (two terminations in parallel): ~60 Ω (±10%)
Single termination resistor (end-to-end) typically 120 Ω per end when measured in-circuit as two 60 Ω parallel

Diagnostic algorithm

Read and record all DTCs and freeze frame/live data with a scan tool. Note which modules report communication loss.
Check battery state and grounding: ensure battery ≥12.4 V at rest and good chassis and engine grounds.
Visually inspect CAN connectors, harnesses, and junctions nearest modules reporting issues. Repair any corrosion/damage.
With ignition OFF, disconnect CAN network connectors as needed and measure resistance across CAN_H–CAN_L at a main connector. Expect ~60 Ω. If open or much higher, isolate open segment. If shorted to ground or battery, locate shorted section.
With ignition ON (engine off), measure voltages: both lines approx 2.5 V. If a line is stuck high/low, trace wiring and check module transceivers and connectors.
Use an oscilloscope to capture H/L waveforms while reproducing the fault. Look for missing recessive edges, excessive noise, or dominant timeouts (bus-off). Compare to a known-good waveform.
If a specific module’s transceiver is suspected, disconnect that module and re-check the bus. If fault clears, confirm by substituting/removing module per service procedures.
Perform wiggle and flex tests on harnesses while observing live data to find intermittent connections. Check splice points and junction boxes.
Check termination resistors and replace if out of tolerance. Re-test communication.
If wiring and terminations pass, check for required software updates/configuration mismatches at dealer-level tools and reprogram or replace the faulty module per manufacturer guidance.
Clear codes and retest to verify repair. If intermittent persists, consider extended road test with data logging.

Likely causes

Loose or corroded multi-pin connector at a gateway or ECU
Faulty CAN transceiver on gateway or one module causing bus errors
Open/shorted splice or connector in main CAN trunk
Failed termination resistor or disconnected end-of-line module
Low battery/poor chassis ground causing communication glitches

Fault status

⚠️ Status

General CAN fault detected — communication error on CAN network (message loss, bus errors or electrical fault). Not otherwise characterised; further wiring, termination and module tests required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours

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