Powertrain, generic · Auxiliary emission controls

P04F4 Catalyst Heater Circuit Low 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. P04F4 concerns the heated catalyst of bank 1. The code means the measured voltage or current in the heater circuit is too low for the commanded state – typically the feed or the heating element is shorted to ground; depending on the driver also an open circuit. The heater is switched off. 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

Feed shorted to ground (chafed at the exhaust, heat)
Heating disc shorted to its housing (insulation damage)
Connector wet or corroded
Power switch or module faulty

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

P04F5P04F2P04F6P0429

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