U0425
Invalid Data Received From Auxiliary Heater Control Module
Communication network
Generic OBD-II
Low
What it means
U0425 is a network communication code: a module is receiving data from the auxiliary heater control module that is corrupt, missing, or out of range. This module runs a booster or fuel-fired heater that helps warm the cabin, common on diesels and in cold climates. The fault affects heating comfort only, not the engine or safety systems, so it's a low-urgency code.
Low
Can I keep driving? Safe to drive — this affects the auxiliary/booster heater, not engine or safety systems; cabin heating may be reduced in cold weather.
Common symptoms
What you'll notice
- Weak or no output from the auxiliary/booster heater in cold weather
- Auxiliary-heater or climate warning message
- Slow cabin warm-up, common on diesels and cold climates
- Other network warning lights may appear at the same time
Common causes
Most likely first
- Internal fault in the auxiliary heater control module sending corrupt dataLikely
- Wiring or connector problems on the bus to the heater moduleCommon
- Low system voltage or a poor ground at the moduleCommon
- Fuel-supply or glow-element fault on fuel-fired auxiliary heatersLess often
How to diagnose & fix
Work through it in order
- Scan all modules and record freeze-frame data; clear any lost-communication codes first.
- Check battery voltage and the heater module's ground.
- Inspect the module connector and bus wiring for corrosion or loose pins.
- On fuel-fired heaters, check fuel supply and the heater's own fault codes.
- If wiring and power are good, suspect the auxiliary heater control module and confirm with manufacturer tests.
FAQ
Quick answers
Is it safe to drive with U0425?+
Yes. The auxiliary heater only supplements cabin warmth. You may notice slower heating in cold weather, but nothing that affects driving safety.
Can I just clear U0425?+
It returns while the module reports bad data. Diagnose the wiring, power, and module rather than only clearing the code.
Related codes
Often seen with U0425
Read & clear U0425 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX