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OBD Code U0664

Lost Communication With Rear HVAC Air Cutoff Actuator

CodeU0664
DescriptionLost Communication With Rear HVAC Air Cutoff Actuator
SystemNetwork

What Does U0664 Mean?

Lost Communication With Rear HVAC Air Cutoff Actuator. This diagnostic trouble code (DTC) is stored when the vehicle's onboard computer detects an issue with the network.

Code Breakdown

U = Network code

0 = Generic (SAE standard)

How to Fix U0664

Follow these diagnostic steps to identify and resolve the issue. Always start with the simplest checks before moving to more involved repairs.

  1. Check the blend door actuator — a clicking noise from the dash is a common sign of failure.
  2. Inspect the blower motor and resistor. Test blower motor by applying 12V directly.
  3. Check the cabin air filter and replace if clogged.
  4. Inspect the A/C compressor clutch engagement.
  5. Test the HVAC control head and its connectors.
  6. Check the temperature door position sensor if equipped.
  7. Replace the failed component and clear codes.

Note: These are general diagnostic guidelines. Some vehicles may have model-specific procedures. Always consult your vehicle's service manual for exact specifications and torque values. If you are not comfortable performing these steps, visit a qualified mechanic.

Frequently Asked Questions

Is U0664 serious?

The severity depends on the underlying cause. Some triggers for U0664 are minor (like a loose gas cap), while others may indicate a more significant problem. We recommend having the code diagnosed with a proper scan tool to determine the exact cause before deciding on urgency.

Can I clear U0664 myself?

You can clear any OBD-II code with a code scanner or by disconnecting the battery for 15-30 minutes. However, clearing the code without fixing the underlying problem will cause it to return — usually within one or two drive cycles. If the code triggered the check engine light, the light will come back on. Fix the root cause first, then clear the code.

How much does it cost to fix U0664?

Repair costs vary widely depending on the root cause. Some fixes are free (like tightening a gas cap) while others can cost several hundred dollars (like replacing a catalytic converter or oxygen sensor). A proper diagnosis with a professional scan tool — not just reading the code — is the first step to getting an accurate repair estimate. Many auto parts stores offer free code reading, but a thorough diagnosis usually requires a mechanic.

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