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Discussion Starter · #1 ·
Hey, so my 2000 Hyundai Accent Hatchback (manual) is tripping the code P0422 (Main Catalyst Efficiency Below Threshold (Bank 1)). If i clear the code it will pop back up after about 40-60 miles of driving. I hooked my OBDII sensor to it and look at the voltage output from the two O2 sensors and the front one oscillates between .2 to .7V and the downstream one does as well switching about at the rate. From my understanding the downstream O2 sensor should stay fairly steady or at least switch much slower than the upstream one. I get pretty good gas mileage, typ. ~30mpg. Luckily my state does not have emission testing. Any idea if it is actually the catalytic converter, the downstream O2 sensor or something else? Any help would be appreciated. Thanks!
 

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sounds like the cat has been killed. poor fluffy!

you're doing the right thing by checking the o2 sensors...but you're within the correct range and the ECU is actually pretty good at figuring out if the sensor is trashed.....sorry :(

i'd look up that error code on www.hmaservice.com under DTC section though....just to be sure before getting an expensive part like the cat.
 

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Discussion Starter · #3 ·
Weirdly done see 2000 Hyundai listed under DTC?

Is there any problems with not replacing it if gas mileage doesn't change? Just wondering.
 

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If front and rear ox sensor toggle "mirror" each other, you know the cat brick is non-existent.. hence the efficiency code.. cost is not horrible, I want to say $400 for the manifold/catalyst, maybe $25 for the 2 gaskets and new nuts.. hopefully old OX unscrew from old manifold for use in new manifold, if not, add another $130 maybe
 

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$400 for a part is a lot to a cheapskate like me :p

problems from not replacing it would be:

- loss of some engine efficiency, possibly power as well. yes gas mileage can possibly be affected, possibly not depending on the mode of failure.

- you WILL fail an emissions test if you need one. that i can promise.

- call me a tree hugger, but you are polluting. it's irresponsible.
 

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Discussion Starter · #6 ·
Another bit of information, after I cleared the code, after about 30mi or so P1128 code tripped. Any idea if this still points to cat or something else?
 

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had trouble finding this on hma, but that code is for running lean. yes its possible that the electronics are falsely detecting a bad cat. i'd say take care of the running lean before anything else. had any misfires?

supposedly the MAP sensor is known to fail and there may be a TSB and computer reprogram regarding this...might be worth a look. also worth taking the MAP sensor out and checking to see if its all blocked up with crap.

other issues: failing fuel pump or blocked filter. if the filter has never been replaced, this is one of the few times i would recommend just doing it. its a cheap part and easy to replace. still, the fuel system pressure should be checked regardless to rule out a failing pump.

vacuum leaks are a big possibility here. intake manifold gaskets are known to go if original. another easy fix. look for broken or cracked vacuum tubing. the easy check is a can of the quick start fluid. spray it anywhere you have an intake gasket or vacuum tubing. the idle will pick up if you find a break. take your time so there's no second guessing the location.

check your plugs. here's a good reference:



lower right 3 you're interested in here.
 

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Discussion Starter · #8 ·
Thanks for the reply. As for the spark plugs, they were just recently replaced. Haven't had any misfires. I bought some CFC cleaner and cleaned the MAF, but it looked really good anyway. I hadn't seen the TSB on computer reprogram, but will try looking that up.
I believe the fuel pump is the original and also think the fuel filter is the original as well.
When you replace the fuel filter do you need to drain the lines of all gas?
Is checking the fuel system pressure easy, or should I take it in to have that done?
Will also look into the possibility of a vacuum leak. Would there be any other symptoms exhibited?
Any way to know that it is running lean other than the tripped code?
 

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Thanks for the reply. As for the spark plugs, they were just recently replaced. Haven't had any misfires. I bought some CFC cleaner and cleaned the MAF, but it looked really good anyway. I hadn't seen the TSB on computer reprogram, but will try looking that up.
I believe the fuel pump is the original and also think the fuel filter is the original as well.
When you replace the fuel filter do you need to drain the lines of all gas?
Is checking the fuel system pressure easy, or should I take it in to have that done?
Will also look into the possibility of a vacuum leak. Would there be any other symptoms exhibited?
Any way to know that it is running lean other than the tripped code?
check the plugs anyhow. you're missing the point here. its not about the plugs being new or old, its about the deposits on them. indicates problems and gives you clues.

cleaning the MAP sensor (these cars do not have MAF sensors) is a great step but does not prove the sensor defective or not. voltmeter is a good way. if it comes down to it, yes sometimes you have to take the blind leap and replace the part most suspected. it should be left as a last resort however.

no idea what CFC cleaner is, but if we're talking engine/injector cleaner don't waste your time. a can of carb cleaner and a set of brushes is the way to go.

fuel pump being original is ok, these pumps hyundai makes rarely break. the filter may be getting blocked and for the cost replace it before anything else. you shouldn't need to drain anything (its under the back seat on top of the gas tank) but use a good wad of disposable rags to soak up any leaked gas.

the test is simple, its a cheap pressure gauge. detach the supply line from injector rail and attach the T piece, reattach to rail. run the car.

vacuum leaks usually present with misfires. you may not be able to feel them, but the ECU will know and will record them even with no engine light on. may also produce EVAP errors.
 

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I had the same problem..see my thread from last month
http://www.hyundai-forums.com/183-lc-2000-2005-accent/177177-2000-accent-hatchback-code-p0422.html

If your front and rear O2 sensors are mimicking each other, the cat is bad. I got mine from RockAuto.com, at a very decent price..and it solved the problem! The problem was a leaky flex pipe originally (see above thread) that caused the computer to think the engine was running lean (one of your codes) and it enriched the fuel mixture, causing the cat to fail. Before you change the cat, I definitely recommend you inspect the exhaust system (especially the flex pipe) for leaks! If you don't fix this problem, a new cat will fail as well!

Regards
Steve
 
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