U0164 Explained: Lost Communication With HVAC Control Module

Quick answer

• What the code means: The U0164 code means your car's main computer has lost its connection with the Heating, Ventilation, and Air Conditioning (HVAC) control module.
• Severity: Low. It is generally safe to keep driving, but your climate control system may not work.
• Most common cause: A dead or weak battery is the most common cause of a U0164 code.

What the U0164 code means

The official OBD-II definition for U0164 is "Lost Communication With HVAC Control Module." In plain English, this means the network of computers in your vehicle (called the CAN bus) can no longer get a signal from the specific computer that controls your heat and air conditioning.

Your car has numerous small computers called control modules that manage everything from the engine to the airbags. These modules "talk" to each other over the Controller Area Network (CAN) bus. When you adjust the temperature or fan speed, you're sending a command to the HVAC control module. If this module stops communicating on the network, the other modules will notice and trigger the U0164 code.

Common symptoms

If your vehicle has a U0164 code, you may experience one or more of the following symptoms:

• The check engine light is on.
• The HVAC system (A/C, heat, and fans) does not work at all.
• The HVAC system is stuck on one setting and cannot be changed.
• You cannot adjust the temperature, fan speed, or vents.
• A "No Comms" or similar message may appear on the climate control display.

Common causes

The most common causes of a U0164 code, ranked from most to least likely, are:

1. A dead or weak battery: Low battery voltage can cause communication issues between control modules.
2. A blown fuse: The HVAC control module has a dedicated fuse. If this fuse blows, the module will lose power and stop communicating.
3. CAN bus wiring issues: The wires that connect the HVAC module to the CAN bus can become corroded, shorted, or disconnected. This is more common in vehicles that have had recent repairs or have been in an accident.
4. A faulty HVAC control module: The module itself can fail, which is the least common cause. This is often a "last resort" diagnosis after all other possibilities have been ruled out.

How a technician diagnoses it

A technician will typically follow these steps to diagnose a U0164 code:

1. Check for other codes: The first step is to scan the vehicle for any other diagnostic trouble codes. If other "U" codes are present, it may indicate a wider network problem rather than an issue with just the HVAC module.
2. Check the battery: The technician will test the battery to ensure it is fully charged and in good condition. A reading of 12.4 volts or higher is good; anything below 12 volts could indicate a problem.
3. Inspect the fuses: The technician will locate and inspect the fuse for the HVAC control module. If the fuse is blown, it will be replaced.
4. Perform a visual inspection: The technician will visually inspect the wiring and connectors for the HVAC control module and the CAN bus. They will look for any signs of damage, corrosion, or loose connections.
5. Use a scan tool: A professional scan tool can be used to attempt to communicate directly with the HVAC control module. If the scan tool cannot establish communication, it confirms the presence of a fault.
6. Test the CAN bus: The technician may use a multimeter or an oscilloscope to test the integrity of the CAN bus wiring. They will look for proper voltage (around 2.5 volts on both CAN High and CAN Low wires) and signal patterns. A good signal will be a clean, square waveform. A bad signal may be erratic or non-existent.
7. Test the HVAC control module: If all wiring and connections are good, the final step is to test the HVAC control module itself. This may involve checking for power and ground at the module's connector. If power and ground are present but the module is not communicating, the module is likely faulty and will need to be replaced.

Typical repair cost

The cost to repair a U0164 code can vary widely depending on the cause of the problem.

• Fuse: A blown fuse is the cheapest and easiest fix, costing only a few dollars for the part.
• Wiring repair: If the issue is a wiring problem, the cost can range from $100 to $500 or more, depending on the extent of the damage and the labor involved.
• HVAC control module replacement: Replacing the HVAC control module is the most expensive repair, with parts ranging from $200 to $800 or more, and labor costing an additional $100 to $300. In some cases, the new module may need to be programmed to the vehicle, which will add to the labor cost.

Can I keep driving with this code?

Yes, it is generally safe to keep driving with a U0164 code. The code indicates a problem with the climate control system, which does not affect the drivability of the vehicle. However, you will not be able to use your air conditioning or heat, which can be uncomfortable in extreme weather conditions. It is recommended to have the issue diagnosed and repaired as soon as possible to restore the full functionality of your vehicle.

Related codes

• U0100: Lost Communication With ECM/PCM "A"
• U0121: Lost Communication With Anti-Lock Brake System (ABS) Control Module
• U0140: Lost Communication With Body Control Module
• U0155: Lost Communication With Instrument Panel Cluster (IPC) Control Module

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