OBD-II code family
Catalyst Heater Control Faults (2 codes)
2 related fault descriptions. Use each full code and the exact vehicle service information to identify its circuit, monitored condition, and required tests.
Codes in this family
This is the complete published member list for this guide. Each code retains its own page; shared diagnostic context does not mean that every member has the same test or repair.
What these codes mean
P0429 and P0439 concern catalyst-heater control for banks1 and2. They are distinct from an oxygen sensor’s own heater, a catalyst temperature-sensor input fault and a converter-efficiency result. Identify the actual circuit before choosing a component.
The control architecture can separate a command circuit, power stage and heater load. A generic heater-control label does not identify a familiar relay, supply voltage, feedback method or separately replaceable element. A diagram is also required before treating both-bank faults as proof of one shared fuse or ground.
Have a qualified technician use the manufacturer’s isolation, absence-of-voltage and rated-equipment requirements. Inspect cooled components and test the indicated supply, control and load paths. A continuity beep alone does not establish normal operation under load; equally, an improvised powered test is not a substitute for the correct procedure.
Do not bypass protection, fit a larger fuse, exchange unidentified relays or directly energize an unknown heater. Investigate why a protection device failed. Use the diagnosed part and serviceability information to decide between wiring, control hardware and an assembly repair.
Verify heater control and the applicable monitor after repair. Normal engine operation does not establish a safe waiting period or prove all aftertreatment functions remain available. Follow actual warnings and obtain assistance for severe running problems, overheating, unsafe power loss or exhaust fumes.
Identify the circuit on your vehicle
Match the full DTC, reporting module, and any failure-type suffix to the service information for your exact year, make, model, engine, and equipment. An identifier alone does not establish installed hardware count, location, connector pinout, or a universal measurement.
Where the manufacturer publishes its own meaning for this code, that is the one to work from — it describes the actual component on your vehicle, which the generic definition cannot. Keep the generic description for what it is good for: it tells you which subject area the standard assigned the code to, which is useful context when the two appear to disagree. If they do disagree, follow the manufacturer.