A faulty auxiliary heater control module, often due to internal electronics failure or water intrusion.; Damaged or corroded wiring and connectors between the auxiliary heater module and the communication bus.; Low voltage or a weak battery causing the module to send corrupted data.; A software glitch in the auxiliary heater module requiring a reflash or update.; Poor ground connection for the auxiliary heater module or the body control module.; A failing communication bus (CAN, LIN, or other) that intermittently disrupts data transfer.; Aftermarket accessories or improper repairs that interfere with the communication network.

DTC codes / U04xx · Invalid data received from a module / U0425

U0425Invalid Data Received From Auxiliary Heater Control Module

Q: What does code U0425 mean?

Invalid Data Received From Auxiliary Heater Control Module. U0425 is a communication fault indicating that the auxiliary heater control module is sending data the main computer (often the body control module or climate control module) cannot interpret as valid. The computer has detected a message from the auxiliary heater module that is missing expected parameters, out of range, or otherwise corrupted, so it flags the module as unreliable.

U0425 is a communication fault indicating that the auxiliary heater control module is sending data the main computer (often the body control module or climate control module) cannot interpret as valid. The computer has detected a message from the auxiliary heater module that is missing expected parameters, out of range, or otherwise corrupted, so it flags the module as unreliable.

SystemNetwork

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaInvalid data received from a module

Symptoms you may notice

The auxiliary heater may fail to activate, leaving the cabin cold during remote start or engine-off heating.
A warning light or message on the dashboard indicating a fault with the auxiliary heating system.
The climate control system may default to a reduced functionality mode or blow only cold air.
In some vehicles, the auxiliary heater may run continuously or at full power regardless of settings.
Often no symptoms besides the warning light, especially if the fault is intermittent.
Other unrelated electrical gremlins may appear if the fault is due to a shared communication bus issue.

Common causes, most likely first

A faulty auxiliary heater control module, often due to internal electronics failure or water intrusion.
Damaged or corroded wiring and connectors between the auxiliary heater module and the communication bus.
Low voltage or a weak battery causing the module to send corrupted data.
A software glitch in the auxiliary heater module requiring a reflash or update.
Poor ground connection for the auxiliary heater module or the body control module.
A failing communication bus (CAN, LIN, or other) that intermittently disrupts data transfer.
Aftermarket accessories or improper repairs that interfere with the communication network.

How to diagnose and fix it

Verify battery voltage and condition; charge or replace the battery if it is below 12.4 volts at rest.
Inspect the auxiliary heater module connectors and wiring for corrosion, chafing, or loose pins.
Check and clean the ground connections for the auxiliary heater module and the body control module.
Use a scan tool to read live data from the auxiliary heater module and compare with commanded values.
Perform a voltage drop test on the power and ground circuits to the auxiliary heater module.
If communication is intermittent, wiggle-test the harness while watching live data for dropouts.
If all else checks out, reprogram or replace the auxiliary heater control module following manufacturer procedures.

Before you replace the auxiliary heater module

A weak battery is a common culprit: the auxiliary heater draws high current, and low voltage can cause the module to send invalid data without setting a low-voltage code.
Corroded pins in the connector at the auxiliary heater are frequently overlooked because the connector looks fine from the outside; always remove and inspect the terminals.
This code can be set by a faulty body control module (BCM) that misinterprets valid data, so do not condemn the heater module without checking the BCM's communication with other modules.
Aftermarket remote starters or alarm systems that tap into the communication bus can corrupt messages and trigger U0425.
A software update for the auxiliary heater module often resolves invalid data faults on vehicles that have no wiring issues.

Can I keep driving with U0425?

The vehicle remains safe to drive because the auxiliary heater is a comfort feature, not a safety system. Avoid relying on the auxiliary heater until the fault is repaired, and do not attempt to use remote start heating if the module is misbehaving.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.