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Ron Z.
Ron Z., - Cadillac Tech -
Category: Cadillac
Satisfied Customers: 18866
Experience:  18+yrs experience. State Inspector and Cadillac Diagnostics
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Cadillac dts: i have 2 codes P0420 & P0442 what should be

Customer Question

i have 2 codes P0420 & P0442 what should be my first step the e-check place replaced the gas cap still have codes
Submitted: 2 years ago.
Category: Cadillac
Expert:  Ron Z. replied 2 years ago.
I'm sorry the Tech you requested was unavailable to assist you today. It appears that Tech is currently "Offline". Now that his 15 minute "request lock" has expired, hopefully I can be of some assistance in his place...These codes are not related. They are in two seperate systems. So, unfortunately, you have two different problems here. Let's start with the easy one first...The P0420 is a fairly straight forward code, and a fairly common problem. This code points to a failing Catalytic Converter. The Oxygen Sensors measure the amount of emissions in the exhaust going into, and then out of the converter. When they see that the converter is not "cleaning" the exhaust enough to meet specs, the Converter is deemed "below threshold" and the P0420 is set. Make sure there are no current cylinder misfires. Make sure there are no leaks in the exhaust system. Which, if there were, you should be able to hear. Sounding like a repeating "tick" or "puff" from the exhaust. Usually more prodominate when the engine is cold. Make sure to include the exhaust manifold when checking for leaks/cracks. If these check ok, then most commonly, the Converter is "on it's way out" and will need replacement in the near future. Keep in mind, you will need a replacement converter that meets specs. Those "universal" or "discount" converters sold at some after market parts stores do not meet specs, and will not cure a P0420.The P0442 is a little tougher. This code is very general, and is simply stating there is a "small leak" somewhere in the EVAP System. So, first course of action here would be to have the EVAP System "smoked". This is where a machine forces smoke through the system and any leaks will reveal themselves with a stream of smoke and can be repaired accordingly. If the smoke test proves no leaks, then unfortunately, there will need to be some testing done on the EVAP Purge Solenoid, Fuel Tank Pressure Sensor and the Vent Valve. This will require the use of a scan-tool. A very common fail item on these vehicles is the Fuel Tank Pressure Sensor... however, I would still strongly recommend the testing procedures. Please do the right thing and remember to leave a rating using the stars at the top right of this page or accept the answer so I may be credited for this Q&A. You can ask follow-up questions even after you rate or accept.