diagnostic codes

[RANDY1957]

i have a 99-s-10 with a 2.2 , and the service engine light is on.
i used the code reader at work and it came up with code " po420 "--
catalyst system efficency below threshold--
i would guess that means i need a new catalitic converter?
just wanted to check with you guys on here and see if it could be something else before i go buy one, and does anyone know where i can go online to tell me what the codes mean????

[rlith]

Originally Posted by RANDY1957

i have a 99-s-10 with a 2.2 , and the service engine light is on.
i used the code reader at work and it came up with code " po420 "--
catalyst system efficency below threshold--
i would guess that means i need a new catalitic converter?
just wanted to check with you guys on here and see if it could be something else before i go buy one, and does anyone know where i can go online to tell me what the codes mean????

Could also be your downstream 02 sensor is going bad.

[maxwedge]

Go to Batauto.com and search that code, great tech article there.

[gmtechnician]

DTC P0420 Catalyst System Low Efficiency




<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=320191&evc=sm&pubid=123&cellId =16692&mspsdsubkey=1004#ss1-53063">Circuit Description

A three-way catalytic (TWC) converter is used in order to control the exhaust 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 is present in the exhaust gas. This will convert the HC and the CO into a harmless water vapor and a carbon dioxide, and reduces the NOx, converting the NOx into nitrogen. The catalytic converter also has the ability to store oxygen. The Powertrain Control Module (PCM) has the capability to monitor this process by using a heated oxygen sensor (HO2S) which is in the exhaust stream past the three-way catalytic converter. The HO2S produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. The PCM monitors the catalyst efficiency by first allowing the catalyst to heat up, waiting for a stabilization period while the engine is idling. Then, the PCM adds and removes the fuel while monitoring the reaction of the HO2S. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the O2S 1. When the HO2S 2 response is close to that of the O2S 1, the oxygen storage capability or efficiency of the catalyst is considered to be bad and the MIL will illuminate.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=320191&evc=sm&pubid=123&cellId =16692&mspsdsubkey=1004#ss1-320191">Conditions for Running the DTC

• No active MAP DTC's