ffgus

2000 SS, 28,000 miles. P0420 trouble code. Catalyst efficiency low-bank-1.
Is it possible for the converter to fail at such low mileage? No performance problems at all. Threads I have read do not have specific mileage as to when the cats have failed. Emission testing here in Milwaukee, WI. Before cat O2 sensor culprit?

Latch

iTrader: (8)

It's certainly possible, one of mine failed around 50,000 miles. But you could tell it had failed, it was rattling like CRAZY. If a bad 02 is at fault then I would imagine it's an aft cat sensor.

joecar

The cat efficiency test (P0420/P0430) specifically requires functioning front and rear O2 sensors in order to fail the cat...

i.e. the PCM induces a fueling step and measures the response time from the front O2 sensor to the rear O2 sensor, if the time difference is too short the test fails and the DTC is turned on;

if the rear O2 sensor has failed then it has it's own DTC's and the cat efficiency test is not run;

the cat efficiency can fail if the cat is fouled (carbon, oil, other) of it the catalyst material has been burnt off (misfires or other causes of excessive cat temperature);

i.e. P0420/P0430 point to an immediate cat efficiency failure, and also indicate some other engine problem that induced the cat efficiency failure.

RezinTexas

if you don't have any performance problems, I'm willing to bet it's just the post-cat o2 sensor. In my experience, when a cat truly fails its because its clogged and causes misfires and severe engine performance restrictions.

3rdCoastPowerSports

iTrader: (5)

I agree

joecar

A cat can fail without getting clogged, it then becomes a passthru and triggers P0420/P0430.

FLURY123

Converters always fail due to an engine related issue! You should figure out what caused the failure before replacing the cat..
You can test the converter. With an IR temp gun, measure the temp at the converter inlet and outlet. You should read between 50-100 degrees hotter at the converter outlet if the catalyst is reacting and doing it's job. If the temp is the same front to rear it is just blowing through. If it it hotter at the inlet it is clogged. Do not measure on the flange or the readings will no be accurate, read at the front and rear of the converter body.

Good luck.

ffgus

I found the number 1 cylinder plug wire off today. I reconnected it and reset the code. I did notice a little roughness in idle this morning. Would this cause a PO420 code?

joecar

No.


See "Conditions for setting the DTC" here: http://www.gearchatter.com/viewtopic9010.php

FiredUpZ28

Not directly, but a misfire can trash the cat. Number one cause of cat failure is raw fuel. Thats why manufacturers have misfire detection - because they warranty cats for 8 years/80,000 miles on most cars (if theres no extended coverage, then its even longer).

RPM WS6

iTrader: (3)

Many people seem to forget this. P0420/P0430 only indicate a reduced oxygen storage capacity of the cat (below required emissions efficiency). Contrary to popular belief, this does not directly indicate a "clogged" cat.

As joecar has correctly outlined above, the PCM detects too fast of a response time from the rear O2s as compared to the front O2s during commanded A/F adjustments. The PCM then determines that the cat is allowing increased tail pipe emissions above a preset threshold. You will get this same exact code if you removed the cats completely and had a hollow pipe, thus it is NOT a direct indicator of a blockage.

Their are coatings that can wear off the substrate and cause the cat to be inefficient at scrubbing the exhaust. This is a somewhat common problem with LS1 F-bodies from '00-'02, GM issued a TSB about it.

Cats that become clogged usually do so due to an overheated substrate (too much raw fuel, etc.) that melts/cracks and becomes blocked. Impact damage can also cause this. Getting a P0420/P0430 doesn't automatically mean that anything is clogged at all, just that your tailpipe emissions have increased above a preset range.

RRG75

iTrader: (1)

I recently installed new valve springs due to the exhaust side spring on cylinder one breaking. The car threw a misfire code for cylinder one and a maf code after the spring broke. I replaced all the valve springs, installed new valve seals, valve cover gaskets, plugs, wires, maf sensor....and while it was easy to get to replaced the oil pressure sender, map sensor, took off the intake put new intake seals, replaced all the pcv hose and pcv valve.....

Everything seems to be right, but the car throws code P0420. I clear it, drive about 10 miles or so, and it comes back.

Did the misfire kill the cat? or could something be loose?

carlramsour

i had the same exact code trip in my car today with basically the same thing happening. no loss in power or performance. ive read several places it may just be the rear o2 sensor how do you go about checking to see if the sensor is any good or needs to be replaced? im hoping its that and i dont have to replace the cats.

RRG75

iTrader: (1)

This weekend, I'm going to try swapping the rear oxygen sensors...drivers side to passenger and passenger to driver..if the code switches to the opposite side I'll know it's the sensor. If it stays on the same side then i'm going to figure its the cat.

FiredUpZ28

It is not an 02 sensor problem. OP (and anyone else with a question in this thread) if board members are going to take the time to try and help you out with your issues, then the least you could do to reciprocate is READ THE POSTS. The 02 sensors NEED to work properly to even test catalyst efficiency. I repeat - you do NOT have an 02 sensor issue.