How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Super Mechanic Your Own Question
Super Mechanic
Super Mechanic, Master technician
Category: Chevy
Satisfied Customers: 16818
Experience:  29 yrs. exp., ASE master, cert. in G.M. electrical, a/c, susspension, brakes, electronic steering
Type Your Chevy Question Here...
Super Mechanic is online now
A new question is answered every 9 seconds

what is catalyst system efficiency below threshold

Customer Question

what is catalyst system efficiency below threshold
Submitted: 8 years ago.
Category: Chevy
Expert:  Super Mechanic replied 8 years ago.

Hello and welcome to Just, Super mechanic here. About your vehicle.


Here is a description of the catalyst efficiency. When there is a efficency code, the cat will need to be replaced. Simply means that the cat is not doing it's job.


A three-way catalytic (TWC) converter controls emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and the CO that are present in the exhaust gas. This process converts the HC and the CO into water vapor and carbon dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also stores oxygen. The powertrain control module (PCM) monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the TWC. This HO2S 2, also referred to as the catalyst monitor sensor, produces an output signal that the PCM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emissions efficiently. The PCM monitors the efficiency of the catalyst by allowing the catalyst to heat, then wait for a stabilization period while the engine is idling. The PCM then adds and removes fuel while monitoring the HO2S 2. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the response of the HO2S 1, which is located before the TWC. When the HO2S 2 response is near that of the HO2S 1, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold. If the PCM detects the degraded condition, DTC P0420 sets.


Customer: replied 8 years ago.
this catalyst is new but is universal that is more small them original
Customer: replied 8 years ago.

Este catalitico lo intalamos hace como un mes , es universal y un poco mas pequeno.

Es posible que este sea el problema para el codigo PO420 ?



Expert:  Super Mechanic replied 8 years ago.
It might not do as good a job of cleaning up the exhaust gases, being smaller.

Related Chevy Questions