U0645: Lost Communication With Active Air Dam Module

What it means

A control module has stopped receiving expected network messages from the active air dam module. The effect on airflow and vehicle operation depends on the vehicle's design.

How it works

The active air dam module controls a movable panel that changes airflow around the vehicle, commonly to manage aerodynamic drag or cooling. U0645 is set when a control module no longer receives the expected network messages from that module, so the air dam’s position or operation may be unknown.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Warning light or message related to the affected system
• Active air dam may not operate as intended

How to diagnose it

1. Scan all modules for U0645 and related body or network codes, and save any available freeze-frame information.
2. Check scan-tool data for active air dam status or position, if supported, and see whether the module responds.
3. Inspect the air dam module connector and visible network wiring for damage, corrosion, water entry, or looseness.
4. Check the module’s power and ground circuits against the manufacturer’s specification.
5. Test the network wiring to the active air dam module for opens or shorts using the vehicle wiring information.
6. If wiring and supplies are sound, verify network communication and module operation before replacing the module.

Common fixes

• Reconnect or clean the active air dam module connector.
• Repair damaged network wiring to the module.
• Restore the module’s power or ground supply.
• Replace the active air dam module if its connections and circuits test correctly but communication remains absent.

Can I keep driving?

If there are no other warnings or signs of overheating, the vehicle can generally be driven cautiously to have the fault checked. Pay attention to temperature warnings, since the air dam may affect cooling airflow on some vehicles.