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U04B6 Invalid Data Received From Catalyst Heater Control Module

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

An electrically heated catalyst brings the converter to working temperature right after a cold start. Vitesco's EMICAT heater runs at 12, 24 or 48 V and can draw up to 300 A, has been ordered for 48-volt mild hybrid diesel vans with production planned from 2022, and in high-voltage hybrids is fed by a dedicated DC/DC converter. The electronics that switch this power report heater state and energy to the engine controller. U04B6 is stored when those messages arrive but fail plausibility; no carmaker has published its use of the code. Section (e)(2) of CARB 1968.2 requires OBD to confirm that a heated catalyst reaches its target temperature in time, so the check cannot run without valid data. U01B5 marks lost contact. Expect a MIL and higher cold-start emissions.

Likely causes

Heater control electronics or DC/DC stage faulty
High-current connection to the heater loose or overheated, giving implausible feedback
Bus wiring or connector near the hot exhaust damaged
Module and engine controller software not matching

Symptoms

  • Check engine light on
  • Catalyst monitor readiness not set
  • Engine may idle longer at raised speed after cold start

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–1,500
Time0.5–3 h

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

Parts involved

catalyst heater module

Related codes

U01B5

References: law.cornell.edu, emitec.com, electronics-journal.com, dieselnet.com.