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U01B5 Lost Communication With Catalyst Heater Control Module

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

Electric catalyst heating lets the converter start working within seconds of a cold start. Emitec's EMICAT disc runs on 12, 24 or 48 V and draws up to 300 A; in high-voltage hybrids Vitesco feeds it through a dedicated DC/DC converter, one form of the separate power electronics that make up a catalyst heater control module. U01B5 means the engine controller has lost contact with that unit, so it can neither command heating nor confirm it took place. No manufacturer documents the code publicly. Under CARB 1968.2, section (e)(2), OBD must verify that a heated catalyst hits its target temperature on schedule, and that check depends on the module. The driver sees a MIL; cold starts emit more and warm-up may run less smoothly; U04B6 covers invalid data from the unit.

Likely causes

Heat or corrosion damage at the heater module connectors near the exhaust

Module supply or high-current fuse open

Catalyst heater control electronics faulty

Symptoms

MIL on
Higher emissions and possibly rough running after a cold start

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,500

Time1–4 h

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

Parts involved

catalyst heater modulecan bus

Related codes

U04B6 U0100 U019D

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