U1A2A

Code

Generic U — Network/User

Module-to-module network message timeout

Brand: Generic

Type: U — Network/User

Views: UK: 20 EN: 34 RU: 22

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open, short or intermittent wiring on the vehicle communications bus (CAN, LIN, etc.).
Failed or sleeping sender module (software hang, internal fault, or lost power/ground).
Bus termination or wiring topology fault (missing/incorrect resistor, improper splice).
High bus error rate or interference (electrical noise, shorts to battery/chassis).
Software/firmware incompatibility or configuration mismatch between modules.
Connector corrosion, poor pins, or damaged shield/ground connections.

Symptoms

One or more vehicle functions controlled by the missing message not working or intermittent (e.g., instrument cluster, ABS, ADAS features).
Warning lights or messages on dash related to the affected systems.
Stored communication-related U-codes and possibly P- or B-codes in other modules.
No or irregular bus traffic visible on a network scanner/oscilloscope.
Features work after key cycles or are intermittent.

What to check

Read all modules with a capable scan tool; record U-codes and related codes and freeze frame data.
Note which module is the sender and which is the receiver of the timed-out message (scan tool message list or OEM documentation).
Check battery voltage and health; verify power and ground at the sender and receiver modules.
Visually inspect connectors, pins, and wiring harnesses for damage, corrosion, or poor crimps. Wiggle test while monitoring bus traffic.
Using a scan tool or network analyzer, monitor message traffic for the expected message ID and frequency and for error frames.
Measure bus voltages with multimeter and verify termination resistor(s) across the bus (typical ~60 ohms for CAN).

Signal parameters

CAN bus idle (recessive): CANH ≈ 2.5 V, CANL ≈ 2.5 V (each to chassis).
CAN dominant: CANH ≈ 3.5 V, CANL ≈ 1.5 V (differential ≈ 2.0 V).
Termination: two 120 Ω resistors in parallel ≈ 60 Ω across CANH–CANL at rest.
Expected message intervals: periodic messages often 10–500 ms; a timeout typically occurs when expected message is missing for 1–3× its period (OEM dependent).
Bus traffic: steady message stream on a healthy network; excessive error frames or silence indicates fault.
Error counters: increasing TX/RX error counters or bus‑off state indicate a transmitter problem.

Diagnostic algorithm

Retrieve all codes from all modules and record freeze frame/vehicle conditions. Note which module logged U1A2A and identify the expected message source.
Attempt to reproduce the fault (key cycles, drive cycle, reproduce feature) while monitoring network traffic live with a scan tool or network monitor.
Verify battery voltage and check power/ground at both sender and receiver modules; repair fuses or grounds if faulty.
Visually inspect and perform wiggle tests on relevant wiring and connectors; repair any damaged wiring or corroded terminals.
Use a multimeter to check termination resistance across bus; if termination not present or out of range, inspect wiring to both ends of the bus.
Use an oscilloscope to capture CAN/LIN waveforms at the module harness; check for correct voltage levels, noise, missing frames or dominant states.
If excessive errors or noisy lines are present, isolate segments or disconnect non‑OEM devices to find the fault.
If one module is not transmitting but has good power/ground and correct bus signals, attempt software reflash or replace the module per OEM guidance.
Clear codes and re-test after repairs; monitor for recurrence and check for any related codes that reappear.
If the fault persists, consult OEM wiring diagrams, message lists, and technical service information or escalate to module specialist.

Likely causes

Intermittent CAN/LIN wiring fault or connector (most common).
Unpowered or failed sending module (fuse blown, ground open).
Excessive bus errors caused by contaminated connector or aftermarket device.
Missing or damaged termination resistor(s).

Fault status

⚠️ Status

Communication timeout: expected network message from another module was not received within configured timeout. Fault logged when receiving module detected missing or delayed message; check bus activity, sender module status, and wiring.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours