U0425: Invalid Data Received From Auxiliary Heater Control Module

What it means

A receiving module has received invalid data from the auxiliary heater control module. The code identifies a data validity problem; the affected function depends on the vehicle.

At a glance

• Usually lights the warning light of the system that lost communication

How it works

The Auxiliary Heater Control Module manages or reports operation of an auxiliary heating system, where fitted. U0425 sets when another module rejects data from that heater module as invalid; the code alone does not establish whether the heater itself or network communication is at fault.

Common causes

Most likely first.

1. Rolling code out of sync
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules and record freeze-frame and communication codes to check whether the auxiliary heater code coincides with broader network faults.
2. Confirm whether an auxiliary heater is fitted and note any heater warning or loss of auxiliary heating.
3. Inspect the heater module connector and network wiring for looseness, corrosion, moisture, or damage.
4. Check the heater module's power and ground circuits against the manufacturer's specification before testing the network.
5. Use a scan tool to review heater module data and communication status, then test the CAN network and gateway routing using vehicle service information.
6. If basic circuits pass, verify any applicable software or configuration updates; test CAN termination only by the manufacturer's procedure rather than assuming a resistor fault.

Common fixes

• Secure or repair a loose or corroded auxiliary heater module connector.
• Repair damaged network wiring to the heater module.
• Correct the module's power or ground fault.
• Resolve an applicable gateway routing or software configuration issue.
• Repair or replace the heater module if its supply and network circuits test correctly but its data remains invalid.

Can I keep driving?

If the auxiliary heater is unavailable but the vehicle otherwise operates normally, driving is generally unaffected; allow for a colder cabin and use the vehicle's normal demisting controls. Stop if there is a separate warning, electrical smell, or sign of overheating.