P0429: Catalyst Heater Control Circuit/Open Bank 1

What does P0429 mean?

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. P0429 is the electrical check of the catalyst heater of bank 1 (the side with 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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

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

Common causes

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

Likelihood is a general estimate across vehicles; your make and model may differ.