What it means
The HVAC Control Module is present on the data bus but the values it reports are implausible — out of range, frozen, or failing the checksum or rolling-count check. The receiving modules reject the data. Automatic climate control behaves erratically. Causes include a faulty sensor feeding the module, internal computation errors, a software or calibration mismatch after a repair, or bus interference corrupting the frames.
How it works
The HVAC Control Module manages heating, ventilation, and air conditioning functions and shares climate system data with other modules. U0424 sets when another module rejects data from the HVAC module as implausible, which can affect automatic climate operation without identifying a particular failed HVAC component.
Common causes
Most likely first.
- HVAC module internal fault
- CAN corruption causing checksum errors
- Gateway module routing CAN messages incorrectly
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
- Scan all modules and save freeze-frame and communication codes to determine whether the HVAC data fault is isolated or accompanies wider network problems.
- Check whether climate controls, automatic temperature regulation, or related displays behave erratically, and note whether the problem is intermittent.
- Inspect HVAC module connectors and accessible network wiring for looseness, corrosion, moisture, or damage.
- Check HVAC module power and ground circuits to the manufacturer's specification and review relevant sensor readings for implausible or frozen values.
- Test network communication and gateway routing using the vehicle's service information, and check for software or configuration mismatches after recent repairs.
- Consider module repair or replacement only after its inputs, power, grounds, and network circuits pass.
Common fixes
- Repair a loose or corroded HVAC module connector or network wire.
- Repair a faulty climate sensor or input circuit feeding implausible data.
- Correct a gateway routing or configuration problem.
- Apply an applicable HVAC module software or calibration update.
- Replace the HVAC module if its inputs and circuits are sound but its reported data remains invalid.
Can I keep driving?
If the HVAC system cannot clear the windscreen or maintain a safe cabin temperature, stop and address that problem before continuing. Otherwise, the invalid-data fault may mainly affect climate operation, but should still be diagnosed.
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.