Network, generic

U05A6 Invalid Data Received From Reductant Heater Control Module

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Diesel exhaust fluid freezes at about -11 °C, and EU rules demanded that it be usable within 20 minutes after a start at -15 °C, so tanks, pumps and lines get electric heaters. Where these heaters are driven by a separate control module, it reports heater states, temperatures and faults to the engine or dosing controller over the bus. U05A6 is stored when those reports arrive but are inconsistent or corrupt. No manufacturer documents this code publicly. CARB 1968.2 requires every component that feeds the emission control or its inducement to be monitored, which covers thaw control. U02A5 means the module is silent, P20B9 points to a heater circuit itself. In cold weather, dosing may start late and warnings may appear.

Likely causes

Heater control module electronics faulty
Water or salt corrosion at module connector or bus wiring
Software levels of heater module and engine controller do not fit

Symptoms

  • Check engine light or DEF system warning
  • Delayed DEF dosing after cold starts

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–800
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant heater module

Related codes

U02A5P20B9U05A3

References: en.wikipedia.org, law.cornell.edu.