Common Symptoms
- Check Engine Light illuminated
- No noticeable drivability issues in most cases
- Slight decrease in fuel economy
- May fail emissions test
- Possible sulfur or rotten egg smell from exhaust
Most Likely Root Causes
- Catalytic converter degradation or failure on Bank 2
- Faulty downstream oxygen sensor on Bank 2
- Exhaust leak before catalytic converter on Bank 2
- Engine oil consumption or coolant burning contaminating catalyst
- Faulty upstream oxygen sensor providing incorrect readings
Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.
AI walks you through every test — one step at a time. Plans start at $12.95/mo.
Component Location
Bank 2 catalytic converter is located in the exhaust system on the side of the engine opposite cylinder number one.
Manufacturer Notes
Some manufacturers have updated catalyst monitoring software to reduce false positive P0431 codes on certain model years.
Also diagnosing J1939 SPN/FMI codes?
Heavy-duty trucks often throw both OBD-II and J1939 faults simultaneously. AI Diesel Tech handles both protocols in a single guided session.
AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician. Professional-grade OBD-II and J1939 fault analysis — trusted by technicians nationwide, used in shops, fleets, and training programs.
Get AI-Guided Diagnosis for P0431
The diagnostic engine walks you through every physical test — step by step, on your phone, at the truck.