Question about 2002 Buick Century

1 Answer

2002 Buick Century Code P0420

Had in-laws car checked @ the dealer for lack of power earlier on. Came back with back converter. They're price was too high so had done elsewhere. After replacement, getting code P0420, which is catalyst efficiency error. Did correct run time for cat to lite up, checked 02 operation and the post 02 sensor wasn't switching properly. Replaced. Week later still getting code. Checked for alternatives ie high octane gas. possible bad converter..but wondering if anyone has access to TSB's for the above vehicle. Wondering if there was a PROM update to reduce the sensitivity of the calculation for aftermarket 02 sensors, so the code doesn't set as much. Didn't get much help from the dealer service advisor when I asked him.

Posted by on

  • Chris B Jul 03, 2009

    Yep I did that too fuel pressure is great



1 Answer

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 10 achievements.


    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • Expert
  • 158 Answers

Sounds as if yoou are actually having a fuel system problem.You need to rreplace the fuel filter and then check the fuel pressure. You should have around 50 psi. If the fuel filter stops up it will cause the exhast to starve for fuel and can damage a catalyst converter. You can get the fuel filter for about 15 dollars at any local parts house.

Posted on Jul 02, 2009


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

2006 Buick Rendezvous P0420 Code.

P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1) P0420 code means that either the upstream or downstream oxygen sensor in the catalytic converter is not working. In short your catalyst is worn out.

Feb 07, 2018 | Buick Cars & Trucks

1 Answer

How many times does the catalytic converter test have run before the code P0420 clears.

You need to put a scanner on the car and clear the codes and see if they come back. Normally you need to drive approx. 50 miles for the computer to cycle through all of the checks it makes.

Oct 16, 2015 | 2002 Buick Park Avenue

1 Answer

Will an open vacuum leak cause a PO 420 code?

Hey Frank how's it going ? Most usually A vacuum leak causes a P0171 lean code ! So I thing your cat is worn out ! P0420 How To Diagnose Bad Catalytic Converter EricTheCarGuy

Jan 16, 2014 | 2002 Buick Century

1 Answer

1998 buick century code p0420

code p 0420 refers to cat converter system bank 1---efficiency below threshold====causes ---cat converter---wiring---HO2S (heated oxygen sensor, the one in the exhaust manifold before the cat converter)
code p 0300 is random misfires
I would suggest changing the HO2S as it reports to the ECM on exhaust content so that the ECM can adjust the air/fuel ratio
so it is logical that if that unit is not reporting correctly, the cat converter may be having trouble burning off the gasses correctly
The oxygen sensor(O2S) reads the results of the cat converter operation and helps fine tune the ECM settings

Mar 10, 2017 | 1998 Buick Century

1 Answer

I put fuel injection cleaner in my 01 buick century. after my tank had almost been empty (quarter tank left), my engine light came on. obd 2 said p0420 cade. my question is could the carbon build up from...

Yes it is possible if the injector cleaner had any amount of lead in it. Most often it's the catalytic converter that is the problem, and causes the sensor to set the code.
I hope this helps.

Aug 25, 2011 | 2002 Buick Century

1 Answer

I have a 2002 buick century and have replaced catalytic converter and both oxygen sensor and the check engine light is still on ... getting dtc codes p0420 and p1134 ..

Reset the ECM by taking out the negative battery terminal off your battery and leaving it aside for several minutes.

Jun 14, 2011 | 2002 Buick Century

1 Answer

Please i really need to get my reset code for my Buick century 2002

Are you talking radio code? If so you need to call Buick dealer and provide your VIN# to get code for theft deterrent radio, they're the only source.

Mar 02, 2011 | 2002 Buick Century

2 Answers

Check engine light on, code reads p0420

Hi and welcome to FixYa!

Code p0420 means Catalyst System Efficiency Below Threshold (Bank 1). This will surely needs attention to resolve the problem.

Hope this helps and thank you for using FixYa! Have a good one!

Jan 26, 2011 | 1999 Buick Century

2 Answers

2005 Chevy Avanlanche running bad

what is the code, P0420?? if its the cat converter is bad why is the dealer clueless? how many miles?? converter has 8/80k warranty. if the converter is plugged up it will run bad, no power stall..... its the same as being constipated.

Sep 25, 2009 | 2005 Chevrolet Avalanche

Not finding what you are looking for?
2002 Buick Century Logo

1,061 people viewed this question

Ask a Question

Usually answered in minutes!

Top Buick Experts


Level 3 Expert

81400 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22326 Answers

Ronny Bennett Sr.
Ronny Bennett Sr.

Level 3 Expert

6927 Answers

Are you a Buick Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides