sam_acura_2012

Acura tl 99 displayed P0420 in the obd scanner and the dealer said to replace the catalytic convertor. The engine light was reset and hasn't lighted up for a month so far. I changed gas station. I put about 25 miles a day. If the catalytic convertor was the problem, shouldn't the engine light come up after 100 miles when the odb computer was in ready state? Original spark plugs with 150K. Should these be replaced? Anything else? Thank you in advance for any help.

justnspace

iTrader: (1)

if the code hasnt come back, then you're good.
however, if and when it comes back, you'll know what to do; replace the cat if it indeed failed.

SuperGreg

I know it's a different car, but a friend of mine has a Suzuki SX4 and it threw a code for the cat - you can clear the code and it won't come back for a month or two. But, it keeps coming back. Some of these codes are based on readings over a long period of time and not just instantaneous values. And/or the cat could be borderline bad.

gnuts

iTrader: (1)

yes get new NGK plugs. you can put on an O2 defouler which just extends the sensor out of the exhaust stream. That will stop the code from coming up. But that O2 sensor only tells you if the cat is bad. It won't affect the way the car runs. that data is taken from the primary O2 before the cat.

3.2TLc

Yeah, it's time to replace the plugs and run some fuel system cleaner through the next tank of gas.
If the code comes back, consider replacing the 02 sensor.

01tl4tl

150 wow are you a record holder as those were due at 100 and most replace around 60-70kmiles
use only the correct NGK Iridiuim or platinum 8 dollars each- very important

you will have years of crud buildup inside- buy 2 cans of Seafoam liquid fuel cleaner ~8 bucks each
Add 1 can to just under half tank= 8 gallons of gas for a max allowed ratio of 2 oz per gal for cleaning strength = drive till fuel light comes on (plenty of gas left- about 50 miles)
then a half tank of 91 octane and drive it off
then a half tank with seafoam added, it will take a few weeks to a month of driving to get all the cleaner run thru, gentle is better in this case
during this time you will do the plugs and perform egr cleaning inside of intake manifold- the other real cause of your problem
That job is super critical on 99s with 1 egr port (later years have 6), every 75kmiles need cleanout

because of the extreme miles on plugs I would NOT do the seafoam blaster method thru master vac port- the plugs are not firing hard and hot enough to burn off the resultant loose carbon and will foul the plugs- makes immediate replacement a must

Do the easy way that gets way more parts of the system clean!
some other cleaning of the throttle body occurs during egr system job too
so the car is ready to run run run

You maybe closing in on time to replace the FRONT O2 sensor- it reads the gasses exiting the engine and adjust the various amounts of air and fuel going in - timing etc,
The rear sensor verifies the cat is working and removing certain pollutants
the front is more common to wear and lose sensitivity
Use DENSO aval everywhere and in this case is the stock OE part maker so its plug and play

on resets- it takes numerous cycles/times of driving, or a concentrated 45 minutes of specifics in order for the ecu to learn everything is ok
Trying to get a safety/smog immediately after reset will get a message saying `not enough info`

01tl4tl

has the timing belt and water pump been replaced?- due at 105/7 years
when you have the intake manifold off to clean egr system- a valve inspect and adjustmen is also due,

Before you do that- add 1/2 a can of seafoam to the oil (throw a new cheap filter on too to catch whats going to be coming! drive 100 miles and change oil/filter with oil warm
That will remove sludge from valve train and make a more accurate adjustment
Precision is key in that job = better mpg better everything

sam_acura_2012

Thank you all. Good news! Spark plugs replaced by OEM parts and engine light has been off for months.

3.2TLc

^^^ Thanks for following up with the resolution !!! EZ fix....

01tl4tl

many here find that after 60-70kmiles = its time for a new set of NGK spark plugs- the 8 dollar each ones