U1A25

Code

Generic U — Network/User

Inconsistent Data from Network Module (U1A25)

Brand: Generic

Type: U — Network/User

Views: UK: 17 EN: 22 RU: 20

AI status

Completed

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Page language: EN

Causes

Faulty or failing network module (ECU) transmitting bad message data
Intermittent or poor electrical connection at module connector(s) (power, ground, CAN/lin wires)
Physical damage, corrosion, or short/open in data bus wiring (CAN/LIN/FlexRay depending on vehicle)
Missing or incorrect module programming or software mismatch after replacement/update
Bus contention or noise (incorrect termination resistors, high impedance, splices, or aftermarket devices)
Low or unstable battery voltage or charging system problems affecting modules

Symptoms

Illumination of MIL or network/system warning lamps
Loss of specific features controlled by the offending module (info display, ABS, transmission, ADAS features)
Intermittent or persistent communication errors visible on a scan tool
Strange/inaccurate messages on driver displays or inconsistent sensor readings
Possible vehicle limp/limited functionality if critical network data are affected

What to check

Connect a capable scan tool and record U1A25 and any related U-codes; note freeze frame and active/inactive status
Check for other network communication codes (U0100, U0073, U0121, etc.) and module-specific faults
Verify vehicle battery voltage and charging system (12.6–14.8 V when running)
Visually inspect connectors and wiring for the suspected module and gateway (look for corrosion, bent pins, water intrusion)
Check physical routing for chafing, aftermarket interfaces (alarms, remote starters) and recent repairs/modifications
Confirm proper module programming/version history if module was recently replaced or updated

Signal parameters

CAN bus: CAN_H ~2.5–3.5 V, CAN_L ~1.5–1.5 V (idle ~2.5 V common mode)
CAN differential idle ~0 V, dominant ~2 V differential; expected clean square wave edges on scope
Message IDs and frequencies for the suspect module (use OEM data or a capture tool to identify expected frames)
Message counters/sequences and checksums: look for non-incrementing counters or checksum mismatches
Bus termination resistance ≈60 Ω end-to-end (two 120 Ω resistors in parallel)
Expected baud rate (common values 250 kbps, 500 kbps, 1 Mbps depending on network)

Diagnostic algorithm

Retrieve and record all codes and freeze frame data; note which module(s) report inconsistent data.
Reproduce the fault if possible (drive cycle or specific operating conditions) and monitor live data for the suspect module messages and related signals.
Inspect battery, grounds, and power supply circuits to the module; measure voltage under load to rule out low/unstable supply.
Visually inspect and wiggle-test connectors and wiring for the module and gateway while monitoring the bus for changes. Repair any damaged connectors/wires.
Scan the bus with a tool that can list all nodes and message traffic; identify missing or malformed frames, unexpected IDs, or duplicate IDs.
Use an oscilloscope to examine CAN_H/CAN_L waveforms at the module connector and at gateway/adjacent nodes; look for noise, reflections, missing recessive/dominant states, or improper levels.
Check termination resistors end-to-end; disconnect modules as needed to isolate a shorted node.
If message counters/checksums are wrong, review recent software updates or module replacements — confirm correct calibration/programming and reflash or reprogram to latest OEM release if required.
Isolate the suspect module by disconnecting it (when safe to do so) and observe whether the inconsistent-data code clears or whether other modules report missing-communication codes; this helps identify whether the module is source of bad data or the network is corrupting messages.
If module is confirmed faulty and reprogramming does not resolve the issue, replace the module with a correctly programmed unit and verify network operation and absence of U1A25.
After repair, clear codes and perform full verification drive; monitor for reappearance of code and related symptoms.