P0429 indicates the powertrain control module (PCM) has detected an open electrical circuit in the catalyst heater control system for Bank 1. The catalyst heater is used to bring the catalytic converter up to operating temperature quickly, and an open circuit means the heater cannot be energized. This typically triggers the malfunction indicator lamp and can cause increased emissions during cold starts.
The internal heating element of the catalytic converter or catalyst heater assembly can burn out or develop an open circuit, preventing current flow. This is the most common root cause for an open-circuit heater code.
The power or control wiring between the catalyst heater, relay, and PCM may be broken, chafed, or melted, creating an open circuit that the PCM detects.
Poor terminal contact, corrosion, or a fully disconnected harness connector at the catalyst heater or relay can interrupt the circuit and set the code.
A blown fuse or a relay that does not close can remove power from the heater element, causing the PCM to register an open-circuit condition.
A rare cause is a PCM that fails to command or monitor the catalyst heater circuit correctly. This should only be considered after wiring, connectors, fuses, relays, and the heater element have been verified.
The vehicle is usually safe to drive, but emissions will be higher until the catalyst warms up. You should have it diagnosed and repaired before an emissions test.
No. If the open circuit is still present, the code and check engine light will almost always return after the next drive cycle or catalyst heater monitor test.
Usually not. The heater element, wiring, connector, fuse, or relay is the far more likely cause. PCM failure is uncommon and should be confirmed by proper circuit testing, not assumed.
Bank 1 is the side of the engine that contains cylinder number one. On an inline engine, there is only one bank, so Bank 1 refers to the sole catalyst heater.