U1730

Code

Generic U — Network/User

Serial Data Bus 'A' Communication Fault

Brand: Generic

Type: U — Network/User

Views: UK: 35 EN: 47 RU: 26

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Page language: EN

Causes

Open, short or high-resistance wiring on Serial Data Bus 'A'
Corroded, loose or damaged connectors on bus wiring or module connectors
Failed control module on the bus
Missing or failed termination resistor(s)
Low battery or intermittent supply/ground to module(s)
Water intrusion or physical damage to harness

Symptoms

MIL (Check Engine) or warning lamps illuminated
Loss or intermittent loss of features controlled by modules on Bus 'A' (eg. instrument cluster, ABS, traction, HVAC, etc.)
Inability to communicate with one or more modules with a scan tool
Erratic or frozen gauge/cluster behavior
Multiple communication-related DTCs present

What to check

Retrieve all related U- and P-codes from all modules; note freeze frame and occurrence count
Verify battery voltage and charging system condition (stable 12–14.7 V)
Visually inspect wiring, connectors, and harness routing for damage, corrosion or water entry
Check for aftermarket devices or recent repairs on the bus wiring
Use scan tool to confirm which modules are not responding
Measure continuity and resistance of bus conductors and shield where accessible

Signal parameters

For CAN networks: recessive state ~2.5 V on each bus wire (CAN_H and CAN_L); dominant causes ~CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ~1.0–2.0 V)
Expected resistance between CAN_H and CAN_L with ignition off and both terminations present: ~60 ohms (two 120 Ω terminators in parallel ≈ 60 Ω)
Open circuit: very high/OL resistance between bus lines or to modules
Short to ground: bus conductor near 0 V; short to battery: conductor near battery voltage

Diagnostic algorithm

Record all codes and data from all modules. Note which modules are not responding to the scan tool.
Verify battery voltage and ground integrity. Recharge if low, then re-check codes.
Perform a visual inspection of bus wiring, connectors and module connectors for corrosion, bent pins, or damage; repair as needed.
With ignition ON, measure voltage at the bus pins of accessible modules; compare to expected idle levels (see signal_params).
Check resistance between CAN_H and CAN_L; confirm proper termination (~60 Ω). If open or shorted, isolate by disconnecting connectors and rechecking until the fault segment is located.
If DMM results are inconclusive or the fault is intermittent, use a lab-quality oscilloscope to monitor bus waveforms during vehicle operation to identify noise, stuck dominant state or missing recessive levels.
Disconnect non-essential modules or suspected module(s) one at a time (with power off where required) to see if the bus returns to normal; use caution and follow manufacturer procedures.
Repair or replace damaged wiring, connectors or termination resistors. If a single module is identified as the cause, replace or reprogram per manufacturer guidance.
After repairs, clear codes, verify communication to all modules and perform a road test under conditions that reproduced the fault to confirm repair.
If fault persists, escalate to manufacturer-specific procedures, wiring diagrams, and module bench testing.

Likely causes

Short to voltage or ground on CAN/serial bus conductors
Intermittent connector or pinned terminal (moisture/corrosion)
Failed module driving the bus (transceiver failure)
Open or high resistance in shield/return or ground circuits
Burnt or missing termination resistor(s) at bus ends

Fault status

⚠️ Status

Serial Data Bus 'A' communication fault detected. One or more modules are not responding or communication is intermittent. Inspect bus wiring, termination, power/ground, and module transceivers.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-4.0 hours