The check engine light came on on my 2004 Pontiac Vibe 1.8. Code PO420 came up on my code reader "catalyst system efficiency below threshold bank 1. Also on the face of the reader the C (cat monitor) O (oxygen system monitor) OH (oxygen sensor heater monitor) and EV (evaporative system monitor) letters were flashing, but no other codes, just the PO420. What is it that needs to be replaced? The catalytic converter or something cheaper like the oxygen sensor? I cleared the code and the check engine light went out, but the red light on the code reader went from red to yellow and has the afore mentioned flashing letters are still there, The car has 142,000 miles on and runs fine. Just passed a smog check in October 2010. Please let me know. Thanks. Ralph

replace the cat converter

EXHAUST RELATED ERROR CODES

There are 711 possible PO generic DTC error codes. Only 7 of the 711 codes are exhaust related.

PO401: Insufficient EGR Flow

PO402: Exhaust Gas Recirculation (EGR) Excessive Flow Detected

PO410: Secondary Air Injection System Malfunction

PO420: Catalyst System Efficiency Below Threshold (Bank 1)

PO421: Warm-Up Catalyst Efficiency Below Threshold (Bank 1)

PO430: Catalyst System Efficiency Below Threshold (Bank 2)

PO431: Warm-Up Catalyst Efficiency Below Threshold (Bank 2)

THINGS TO ASK YOURSELF OR YOUR CUSTOMER

Have there been any driveability or performance issues with the vehicle, have there been any recent repairs or tune-up work performed, if so was the check engine light reset and were the codes recorded on previous repair orders.

Do not rely on scan tool data alone. In most applications, the customer will have the check engine light reset prior to repair. If the original cause of converter failure is intermittent, only the catalyst failure code may show up (masking the original reason for converter failure).

EXHAUST RELATED ERROR CODES

There are 711 possible PO generic DTC error codes. Only 7 of the 711 codes are exhaust related.

PO401: Insufficient EGR Flow

PO402: Exhaust Gas Recirculation (EGR) Excessive Flow Detected

PO410: Secondary Air Injection System Malfunction

PO420: Catalyst System Efficiency Below Threshold (Bank 1)

PO421: Warm-Up Catalyst Efficiency Below Threshold (Bank 1)

PO430: Catalyst System Efficiency Below Threshold (Bank 2)

PO431: Warm-Up Catalyst Efficiency Below Threshold (Bank 2)

THINGS TO ASK YOURSELF OR YOUR CUSTOMER

Have there been any driveability or performance issues with the vehicle, have there been any recent repairs or tune-up work performed, if so was the check engine light reset and were the codes recorded on previous repair orders.

Do not rely on scan tool data alone. In most applications, the customer will have the check engine light reset prior to repair. If the original cause of converter failure is intermittent, only the catalyst failure code may show up

P0420 - Catalyst System Efficiency Below Threshold Bank 1http://engine-codes.com/p0420.htmlForum CodePossible causes- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM) Tech notes The most common cause it the three way catalyst converter Bank 1. Changing just the O2 sensor usually don't repair the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

PO420--Catalyst System Efficiency Below Threshold (Bank 1)

Your Exhaust converter is worn out after 10 years,not too bad,
but should last 12 or 14 years, if engine ran correctly from day one

If you have 2,do them both

Won't pass inspection as is,Emissions are too high

P0430 code is(catalyst efficiency below threshold on bank 2)
P0420 code is((catalyst efficiency below threshold on bank 1)
P0306 code is(cylinder 6 misfire detected)

The PO420 means that the Catalyst System has an Issue'

The actual error is

"Catalyst system below Threshold (bank 1)"

As mentioned above, the code's description is Catalyst System Efficiency Below Threshold (Bank 1). OK, now tell me that again in plain English please.... let's break it down: the catalyst system being referred to is your three-way catalytic converter; so the catalytic converter is not working properly (i.e. it's not efficient). Bank 1 refers to the side of the engine which contains cylinder #1. On inline engines such as 4 & 5 cylinder engines, there is only one bank. So, to really simply things let's just say that the efficiency of the catalytic converter and/or exhaust pipe and/or O2 sensor is not so great.

There are a number of things that could be causing this p0420 catalyst efficiency code. The most common thing is the catalytic converter itself is no longer functioning properly. The other likely thing is the rear O2 (oxygen) sensor is no longer working properly. Other things could include exhaust leaks, damaged exhaust pipes, damaged O2 sensor wiring/connectors, plugged catalytic converter, etc.

You can search for the Information on the web. Just type in the actual error above into you fav search engine!

Hope that helps...

CODE PO420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK I * CODE PO325 KNOCK SENSOR NO.1 CIRCUIT MALFUNCTION BANK NO.1 OR SINGLE SENSOR

P0420 is catalyst system efficiency below threshold (bank 1)

P0440 is evaporative emission control system malfunction

P0441 is evaporative emission control system incorrect purge flow

code po420=catalyst system efficiency below threshold bank #1
code po430=catalyst system efficiency below threshold bank #2
from autozone online
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152800a8b20