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- - Error code PO420 (https://www.buickforum.com/forum/lesabre-24/error-code-po420-680/)

db14399

Dec 19, 2006 07:31 PM

2003 LaSabre with warning light code PO 420. Also antifreeze smell.

Thank you for any advice. Danny

db14399

Dec 20, 2006 03:28 PM

Anyone know where I can find out about this code. Thanks Danny

MrBSS

Dec 20, 2006 08:24 PM

DTC P0420: "TWC System Low Efficiency"...If the PCM detects a level of HO2S 2 activity that indicates the catalyst is no longer operating efficiently, DTC P0420 will be set." TWC is short for three way catalyst.

Apparently your catalytic converter is not working. It may be that an O2 sensor has gone bad. If you smell antifreeze, youcould have a coolant leak that is screwing things up.

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