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U02A5 Lost Communication With Reductant Heater Control Module

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

At roughly -11 °C diesel exhaust fluid turns solid, while EU type approval asked for usable fluid within 20 minutes of a start at -15 °C, so tank, pump and lines carry heaters. Some systems leave their switching to a separate heater control module that reports state and temperatures to the engine or dosing controller. U02A5 is set when this module goes silent. No manufacturer documents U02A5 publicly. Many engines do without such a module: Ford's 2023 diesel summary drives the heaters straight from the engine controller and checks them with output codes such as P20BB, P20BC and P21DD. CARB 1968.2 requires every input to the inducement strategy to be monitored, and thaw control feeds it. In frost, dosing may start late, with a DEF warning and later inducement.

Likely causes

Fuse, relay or supply of the heater module faulty
Water or salt corrosion at the module connector near the tank
Shared bus disturbed by another faulty module
Heater control module internally failed

Symptoms

  • MIL and DEF system warning
  • Dosing delayed in cold weather
  • Inducement countdown if it persists

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–3 h

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

Parts involved

reductant heater modulevehicle bus wiring

Related codes

U05A6P20B9P20BBU02A2

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