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Home / DTC / U0425 — Invalid Data Received From Auxiliary Heater Control Module

U0425 — Invalid Data Received From Auxiliary Heater Control Module

Detailed page for trouble code U0425.

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U0425

HYUNDAI U — Network/User

Invalid Data Received From Auxiliary Heater Control Module

Brand: HYUNDAI
Type: U — Network/User
Views: UK: 16 EN: 38 RU: 22
AI status
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ready
Completed 100%
Page language: EN

Causes

  • Faulty or intermittent communication on CAN/LIN bus between modules
  • Defective auxiliary heater control module
  • Corroded, loose or damaged wiring, connector pins, or ground related to the auxiliary heater
  • Low battery voltage or poor power/ground to the module during message transmission
  • Software mismatch or corrupted module firmware
  • Faults in another module sending invalid data or bus noise

Symptoms

  • Auxiliary heater may not run or starts intermittently
  • Illuminated MIL or HVAC/warning lamp related to auxiliary heater or system communications
  • Related systems may show reduced functionality or throw other communication codes
  • Cold-cabin heating reduced or delayed (if auxiliary heater is used for cabin pre-heating)
  • Possible hard start or reduced engine management responses if auxiliary heater interacts with engine controls

What to check

  • Connect a full-function scan tool and read all stored U and P codes and freeze frame data
  • Check battery voltage (engine off and cranking) and main battery connections
  • Visually inspect and wiggle-test wiring and connectors at the auxiliary heater module and associated junctions for corrosion, bent pins, or loose terminals
  • Inspect fuses and relays for auxiliary heater power circuits
  • Check CAN/LIN bus continuity and resistance between relevant modules and ground
  • Attempt to communicate directly with the auxiliary heater module using the scan tool (identify if module responds)

Signal parameters

  • CAN bus TX/RX messages from Auxiliary Heater Module (message ID and expected message rate per factory data)
  • Message payload fields: temperature setpoint, heater state, diagnostic status (verify values within expected ranges)
  • Bus voltage during message transmission (expected ~12 V nominal; verify no large drops)
  • Frame frequency/period (expected Hz) and message length (bytes) — check for missing or malformed frames
  • Checksum or CRC fields if used by the module’s protocol
  • Module presence/response to diagnostic request (OBD session response)

Diagnostic algorithm

  1. Capture codes and freeze frame with a diagnostic scanner; note other U-codes and timestamps.
  2. Check battery state of charge and charging system. Poor voltage can corrupt messages — repair as required.
  3. Visual inspection: unplug auxiliary heater module connector(s) and inspect for bent pins, corrosion, water intrusion or overheating. Repair or clean contacts.
  4. Verify fuses/relays supplying the auxiliary heater module; replace any blown fuses and retest.
  5. With ignition ON, use scan tool to request module data. If module does not respond or returns malformed data, suspect module or wiring.
  6. Perform wiring checks: continuity and short-to-ground/power tests on bus wires and power/ground circuits to the auxiliary heater module. Repair any faults.
  7. Monitor CAN/LIN bus with a scope or bi-directional scan tool: confirm message IDs, timing, voltages, and correct waveform shape. Look for noise or voltage swings.
  8. If wiring and power/ground are good but messages remain invalid, try reprogramming or updating module software per factory procedure before replacing the module.
  9. If reflash does not correct data, replace the auxiliary heater control module and perform any required relearn or coding procedures.
  10. Clear codes and perform a road or system test to verify the fault does not return; document intermittent issues if fault is not present.

Likely causes

  • Open/short in CAN/LIN data wires or poor connector contact at auxiliary heater module
  • Auxiliary heater module internal failure producing malformed messages
  • Missing or low battery voltage and/or weak ground at time of communication
  • Intermittent bus interference from after-market devices or damaged wiring harness
  • Module learned/calibration or software needs reflash to correct message formatting

Fault status

⚠️ Status
Invalid data received from Auxiliary Heater Control Module — communication/data format error detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 3.0 hours

Similar codes

U0100 U0121 U0140 U0426 U1100
371

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