Powertrain, generic · Auxiliary emission controls

P0439 Catalyst Heater Control Circuit/Open Bank 2

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

An electrically heated catalyst has a heating disc ahead of a support catalyst so that it works soon after a cold start (Emitec EMICAT, 12–48 V); it was tried on Californian petrol cars in the 1990s and is used today mainly on diesels, for example Audi's 3.0 TDI from 2014 and 48-volt diesel vans. P0439 is the electrical check of the catalyst heater of bank 2 (the side without cylinder 1): the module drives it via a relay or power stage and detects an open control circuit or heating element from the driver feedback, as CARB requires for output circuits. The heater then fails, the catalyst lights off later and P0424/P0434 may follow; the engine itself runs normally. No manufacturer document available to us uses this code.

Likely causes

Wire or connector to the heating element open (heat, corrosion)
Heating element burnt out
Relay, fuse or power stage faulty
Engine module

Symptoms

  • Check engine light on
  • Higher emissions after a cold start
  • Otherwise usually unremarkable

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–2,500
Time0.5–4 h

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

Parts involved

catalyst heaterheater relayheater wiringengine control module

Related codes

P0429P0434P0433P0435

References: law.cornell.edu, emitec.com, dieselnet.com.