P0429 Catalyst heater: circuit fault (bank 1)

By: Diagno editorial team · Updated: 2026-10-15

P0429 means: Catalyst heater: circuit fault (bank 1). The catalytic converter cleans the exhaust gas. OK to drive, but have it checked soon. The repair usually costs about €60–250 in Estonia. The most common cause: connector loose, damp or corroded. Other possible causes: wire broken or chafed, faulty sensor.

What it means

The catalytic converter cleans the exhaust gas. The computer compares the oxygen sensors before and after it and found that it no longer cleans well enough. The computer found a fault in the electrical circuit: the part, a wire, a connector or a fuse.

What you may notice

• Engine light on
• Emissions fail the inspection
• Sometimes a rotten-egg smell
• Less power if it's blocked

What could be wrong

1. 1Connector loose, damp or corroded
2. 2Wire broken or chafed
3. 3Faulty sensor
4. 4Engine computer fault (rare)

Repair difficulty: Moderate

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Before replacing an expensive converter, have the oxygen sensors and exhaust leaks checked. That often saves hundreds of euros. Best left to a workshop. It needs a diagnostic tool and experience.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the sensor

Standard SAE description: Catalyst Heater Control Circuit (Bank 1)