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marcpod
marcpod, Own collision repair advice
Category: Audi
Satisfied Customers: 2882
Experience:  i-car/Basf training, 300 repairs and 650,000 in Collision monthly 18 yrs exp/licensed adjuster
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My engine check light is on, has three code: p0491, p0492, p0421

Customer Question

My engine check light is on, has three code: p0491, p0492, p0421. What should I do to repair them? I can not afford a lot of money.
Submitted: 6 years ago.
Category: Audi
Expert:  marcpod replied 6 years ago.

marcpod :

Welcome those are your oxygen sensors and cat converter codes!

marcpod :

You should be able to check your local muffler shops and check prices.

Customer: replied 6 years ago.
Relist: Answer quality.
I need more precisely answer. This answer does not help at all
Customer: replied 6 years ago.
i think p0491 &p0492 might be due to vacumn leak. and p0421 is a result of previous two. Need some detailed suggestion. I do not want to go to dealer
Expert:  marcpod replied 6 years ago.
p0421 is for the cat converter. the bank one and two are the oxygen sensors. You have 4 oxygen sensors. These aren't vacuum leaks these are bad oxygen sensors.
Customer: replied 6 years ago.
so you think which oxygen sensor might be bad. pre cat or after cat? I also have a problem that when I accelerate from stay (like when you start from stop sign or traffic light), the car will have " bing" if accelerate too fast. If accelerate gently, it won't. I checked online, found that it might due to bad EGR valve. Bad EGR valve will also cause p0491 & p0492 code right. p0491 & p0492 means secondary air injection flow too low for both bank. Some one called them p1411&p1423. I do not know if they are the same code.
Expert:  marcpod replied 6 years ago.

They according to the codes shows specifically to the banks before and after the cat. Are getting those codes too? these 2 codes graphic

 

 

graphic

Customer: replied 6 years ago.

hi,

 

The code I got is P0421: catalyst efficiency low-bank 1;

P0491: Secondary air injection system insufficient flow bank 1. Explanation is damaged air system components. Possible cause is Faulty air solenoid valve or Faulty Air system relay.

 

P0492: Secondary air injection system insufficient flow bank 2. Explanation is damaged air system components. Possible cause is Faulty air solenoid valve or Faulty Air system relay.

Expert:  marcpod replied 6 years ago.

Yes the solenoids are the oxygen sensors. That is why I recommended replacing those items. How many miles are on the vehicle!

Customer: replied 6 years ago.
91000 mile. You thought its more possible that the oxygen sensor is broken than the secondary air injection system broken. But if the oxygen sensor is broken. Means both two are broken. I am going to leave america and are selling this car. I want to use the cheapest way to figure out this problem and sell it. Thank you!
Expert:  marcpod replied 6 years ago.
That is what the codes are saying you can get a aftermarket o2 and cat converter go to any muffler shop!