P0422: Main Catalyst Efficiency Below Threshold (Bank 1)

P0422 means the main catalytic converter on Bank 1 has dropped below the efficiency threshold the ECU expects. It is similar to P0420 but used on some manufacturers (notably Chrysler, Jeep, and certain European platforms) to distinguish the main cat from the upstream warm-up cat in multi-brick exhaust systems.

P0422 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0422 and illuminates the check engine light.

If your vehicle has triggered P0422, you may notice one or more of these symptoms:

• Check engine light illuminated
• Slight drop in fuel economy
• Rotten-egg sulfur smell from exhaust
• Possible rattling from under the car (substrate breaking up)
• Failed emissions or periodic technical inspection

Here are the most common causes of P0422, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. Safe for normal driving. The check engine light will prevent emissions or periodic technical inspection passage. If the code is accompanied by rattling under the floor, the converter substrate may be breaking apart internally and replacement should be prioritised.

Follow these steps to pinpoint the root cause of P0422:

1. Read freeze frame data and check for companion catalyst codes (P0420, P0421) that may be active at the same time
2. Inspect the full Bank 1 exhaust run for leaks, especially at flange joints and slip-fit connectors after the main cat
3. Graph the Bank 1 downstream O2 sensor at steady 2,000 to 2,500 RPM. A healthy main cat keeps it stable around 0.4 to 0.6 V
4. If the downstream signal swings more than 0.2 V repeatedly, the main cat is no longer storing oxygen and is failing
5. Test downstream sensor switching speed. Anything over 300 ms is sluggish and may be the actual fault

Repair costs for P0422 vary depending on the root cause and your vehicle. Here are typical estimates:

P0422 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0422 or indicate related issues: