What it means
A control module has detected that the software in the auxiliary heater control module is incompatible with its own software or configuration. Auxiliary-heater operation may be affected; the specific effects depend on the vehicle.
How it works
The auxiliary heater control module manages a supplemental heating system and reports its software and configuration over the vehicle network. U0325 sets when a controller finds that the auxiliary heater module's reported version or setup is incompatible with what it expects, so auxiliary heating may not operate correctly.
Common causes
Most likely first.
- Incorrect or incompatible software in the auxiliary heater control module
- Module replacement without required programming or configuration
- Incorrect module part number
Symptoms
- Auxiliary-heater operation may be affected
- Related warning indicators may illuminate
- A diagnostic scan may show related communication or configuration codes
How to diagnose it
- Scan all modules and save event data, noting which controller stored U0325 and any auxiliary heater or network codes.
- Check whether the auxiliary heater control module or a related controller was recently replaced, updated, or configured.
- Inspect the heater module's connectors and accessible harness for loose connections, corrosion, moisture, or damage.
- Read the auxiliary heater module's identity, software version, and configuration with a scan tool and compare them with the vehicle's required information.
- Check gateway and network records for communication or routing faults affecting the auxiliary heater module.
- Restore compatible software and configuration using the manufacturer's procedure, then rescan and verify heater operation.
Common fixes
- Secure or repair a loose or corroded auxiliary heater module connector.
- Program or configure a replacement auxiliary heater control module for the vehicle.
- Replace an incorrectly specified module with the correct compatible unit.
- Correct gateway routing or configuration if it is disrupting auxiliary heater module messages.
Can I keep driving?
If only the auxiliary heater is unavailable, normal driving is usually possible, but allow for slower cabin warming and reduced comfort in cold conditions. Ensure the windscreen can be cleared using the main HVAC system before driving.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.