Powertrain, generic · Auxiliary emission controls

P0434 Heated Catalyst Temperature Below Threshold 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. P0434 implements CARB's heated-catalyst rule for bank 2 (the side without cylinder 1): the catalyst must reach its intended temperature within a time set by the manufacturer after the start, measured by a temperature sensor or modelled from heating power. If it does not, the heater is too weak – supply voltage, contact resistance, an ageing element – or heat losses are too high. An open heater circuit is reported as P0429/P0439 instead. No manufacturer document available to us uses this code.

Likely causes

Heating element aged or partly faulty
Supply too weak (battery, 48 V system, relay, contact resistance)
Catalyst temperature sensor reads wrong
Engine module or calibration

Symptoms

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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,500
Time0.5–4 h

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

Parts involved

electrically heated catalystcatalyst heatercatalyst temperature sensorengine control module

Related codes

P0433P0439P0424P0435

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