P0428

The P0428 code signals that the PCM has detected a catalyst temperature sensor high input (bank 1 sensor 1) condition. This code relates to the catalytic converter, a critical emissions component that converts harmful exhaust gases into less harmful substances. Reduced catalyst efficiency typically means the converter is no longer adequately processing exhaust pollutants. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: Decreased fuel economy. Check Engine Light (MIL) illuminated. Sulfur or rotten egg smell from exhaust. Failed emissions test. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Contaminated catalytic converter (leaded fuel, silicone). Faulty oxygen sensor providing incorrect readings. Exhaust leak before the catalytic converter. Rich or lean fuel mixture over extended period. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Connect an OBD-II scanner and read all stored trouble codes and freeze frame data. Monitor upstream and downstream O2 sensor readings; compare switching patterns. Check for exhaust leaks before the catalytic converter. Inspect for engine misfires or other codes that could damage the converter. Test the catalytic converter efficiency using a temperature gun (inlet vs outlet). If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our Powertrain (P) collection on OBD Codes. We provide comprehensive, up-to-date information to help you find solutions quickly.