U0425 code meaning
Invalid Data Received From Auxiliary Heater Control Module
What U0425 means
U0425 concerns the auxiliary heater control module, the controller of an extra heat source such as a fuel-fired coolant heater on a diesel. The HVAC or engine controller sets it when the heater's status frames arrive with implausible content. No manufacturer documents U0425 publicly; GM's 2013 bulletin PIP5094 merely includes it in a long list of codes for which terminal fit should be checked before circuit tests. Ford's patent US 10,124,649 shows how such a heater is tied into the network: it talks to the HVAC unit over the bus and to the engine controller through a bus interface, receives ambient temperature from it and runs its own fuel pump. GM's 6.6 L Duramax ECM (2014) watches messages from this module, stating lost contact as U0166, Special Type C. U0325 is software. The heater stays off; no MIL is expected.
U0425 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0425
- Auxiliary or parking heater does not start
- Slow warm-up and weak cabin heat in cold weather
Common causes of U0425
- PossibleAuxiliary heater control unit faulty or locked after an internal fault
- PossibleLow supply voltage at the heater, for example from a weak battery
- Less likelyLoose terminals or corrosion in the heater's bus connector
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Auxiliary heater module
What each part of U0425 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 25 | The exact fault in that area. |
What to do next
- Note U0425 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0425
What does U0425 mean?
U0425 means "Invalid Data Received From Auxiliary Heater Control Module". U0425 concerns the auxiliary heater control module, the controller of an extra heat source such as a fuel-fired coolant heater on a diesel. It is a generic code, so it means the same on every make.
Is it safe to drive with U0425?
U0425 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0425 fail an emissions test?
U0425 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0425 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will U0425 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.