✅ Why Do Catalysts Cause Engine Warning Light On? Over time, the catalyst may begin to lose efficiency due to engine operating conditions or external factors.
Within the most common causes of the catalyst warning light or Check Engine with Catalyst DTC we have:
Com Poor quality fuel or harmful additives:
Why the light is on: Fuel with impurities leaves deposits in the catalyst, limiting exhaust flow. Oxygen sensors detect low efficiency in gas conversion, which causes the ECU to register codes like P0420 or P0430.
( Rich Mix (Over Fuel):
Why the light is on: A rich mixture can be caused by clogged injectors, a dirty air filter, or a faulty airflow sensor (MAF). The ECU compares data from oxygen sensors before and after the catalyst, detecting an increase in hydrocarbon in the exhaust, which activates codes like P0172 or P2097.
al Exhaust oil or coolant step:
Why the light is on: Worn piston rings or damaged valve seals allow oil or coolant to enter the exhaust. This contaminates the catalyst, obstructing and altering the relationship of gases detected by oxygen sensors. The ECU registers codes such as P0420 or P0430.
⏭ Fails in oxygen sensors:
Why the light is on: If oxygen sensors are damaged or react slowly, they send incorrect data to the ECU. This can cause the emission control system to work outside of its parameters, enabling codes like P0133 or P2195.
er Extreme temperatures or restricted flow in the exhaust:
Why you turn the light on: If there are exhaust restrictions, such as a partially clogged catalyst, gas flow and temperature will not be ideal. Post-catalyst sensors detect abnormal values and the ECU activates codes like P0421 or P2096.
✅ List of common DTC Codes related to the catalyst and their explanations:
P0420: Sub-threshold Catalyst System Efficiency (Bank 1):
Detected when rear sensor shows insufficient gas conversion levels.
P0430: Sub-threshold Catalyst System Efficiency (Bench 2):
Similar to the P0420, but affects the opposite bank of the engine.
P0421: Insufficient catalyst heating:
Indicates that the catalyst does not reach its optimal temperature to work efficiently.
P2096: Postcatalyst Poor Mix (Bench 1):
Detected when the rear sensor indicates higher than expected oxygen levels, suggesting poor mix.
P2097: Postcatalyst Rich Mix (Bench 1):
Indicates that the rear sensor detects a high concentration of hydrocarbons, product of rich mixture.
