Invalid Data Received From HVAC Control Module

Possible causes

• CommonA fault inside the HVAC control module, or in a sensor feeding it, so it passes on a reading that is wrong
• CommonThe HVAC control module has its own stored fault codes that explain why its data is bad
• CommonLow or unstable system voltage - a module starved of a steady supply produces nonsense values
• CommonCorroded or water-damaged connector at the HVAC control module, corrupting the message content
• PossibleSoftware or calibration mismatch after the HVAC control module was replaced, updated or coded
• PossibleDamaged wiring, or a repair that disturbed the bus pair
• PossibleInterference from a badly-fitted aftermarket accessory spliced into the bus
• RareA fault in the receiving module, which is misjudging data that is actually good

What you might notice

• Cruise control unavailable or disengaging on its own
• Heating or air conditioning not responding, or stuck at one temperature
• Auxiliary or parking heater not running
• Climate display showing implausible temperatures
• Warning light on for the system that depends on the data
• The affected function switching itself off
• Fault codes stored in more than one module

What to check, in order

1. Read the codes from every module on the vehicle, not just the engine. This code names the HVAC control module as the source, and the HVAC control module almost always has its own code saying why its data is wrong. That code, not this one, is the one to fix.
2. Check battery voltage and the earth points before suspecting any module. A supply that sags makes modules produce implausible values, and it sets invalid-data codes across several unrelated systems at once.
3. If more than one module is reporting invalid data, look at the power supply and the bus rather than at the modules. Modules do not fail in groups; shared feeds, earths and bus wiring do.
4. Find out whether anything was recently fitted, replaced, updated or coded. A replacement module carrying the wrong calibration sends data in a range or format the rest of the vehicle does not expect, and this code is often the first sign of it.
5. Inspect the connector at the HVAC control module for corrosion and water ingress. A partly-corroded pin corrupts the content of a message while the message itself still arrives on time - which is precisely this code rather than a lost communication code.
6. Do not replace the HVAC control module on the strength of this code alone. It is the accused, not the convicted. Confirm the data it is sending is actually wrong - by reading its own codes and its live data - before spending money on it.