Powertrain, generic · Auxiliary emission controls

P04F6 Catalyst Heater Circuit High Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

An electrically heated catalyst has a heating disc ahead of the catalyst so that it works soon after a cold start; Emitec's EMICAT runs on 12, 24 or 48 V and draws up to about 300 A. It is in series production on 48-volt mild-hybrid diesel vans since 2022. P04F6 concerns the heated catalyst of bank 1. The code means the measured voltage in the heater circuit is too high for the commanded state – a short to the supply, a sticking switch or, if measured on the low side, an open heating element. The heater is switched off or runs uncontrolled. No manufacturer document available to us uses this code – Ford, for example, states that heated catalyst monitoring is not supported – so thresholds and warning-lamp logic are not documented; the description follows CARB and patents for the same part.

Likely causes

Wire shorted to the supply
Heating element or feed open (crack, electrode damage)
Relay or power switch sticking
Corroded connector

Symptoms

  • Check engine light on (depending on the maker)
  • Higher emissions after a cold start
  • Otherwise usually unremarkable

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–2,500
Time0.5–3 h

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

Parts involved

catalyst heater bank1heater power switchheater wiringengine control module

Related codes

P04F7P04F2P04F4P0429

References: law.cornell.edu, patents.google.com, emitec.com.