1997 k1500 ses

O.K. I have a P0420 code “the pcm has determined that the catalyst system efficiency for bank 1 is below threshold for the current engine operating conditions”.
Now I am thinking catalytic converters specifically the one on the driver’s side. But could the o2 sensor be bad also?
I can reset the pcm and it comes back after a week or so of driving.
If I can get my hands on a diagnostics tool, does anyone know the voltage and any hints to see if the o2 operating correctly? Or should I compare it to the bank 2 o2?
If it is the converters, how in the hell does it know that they are clogged?

Thanks for the advice in advance,
Richard

130,000 miles
no modifications....

Circuit Description

In order to control emissions of Hydrocarbons (HO), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx), The system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The Vehicle Control Module (VCM) has the capability to monitor this process using the HO2S (Bank 1, Sensor 1). The HO2S (Bank 1, Sensor 3 for the 5.0L) or (Bank 1, Sensor 2 for the 5.7L, 7.4L), located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the HO2S (Bank 1, Sensor 3 for the 5.0L) or (Bank 1, Sensor 2 for the 5.7L, 7.4L) signal will be far less active than that produced by the HO2S (Bank 1, Sensor 2 for the 5.0L) or (Bank 1, Sensor 1 for the 5.7L, 7.4L). If a problem exists which causes the VCM to detect an excessive HO2S (Bank 1, Sensor 3 for the 5.0L) or (Bank 1, Sensor 2 for the 5.7L, 7.4L) activity outside of an acceptable range for an extended period of time, the VCM sets the DTC P0420. This DTC indicates that the three-way catalytic converter's oxygen storage capacity is below a threshold considered acceptable.

Conditions for Setting the DTC



Closed Loop
No Vehicle Speed (VSS) sensor DTCs
No Throttle Position (TP) sensor DTCs
No HO2S DTCs
No Misfire DTCs
No Manifold Absolute Pressure (MAP) sensor DTCs
No Fuel Trim DTCs
No Intake Air Temperature (IAT) sensor DTCs
No Engine Coolant Temperature (ECT) sensor DTCs
No Mass Air Flow (MAF) sensor DTCs
No EVAP DTCs
No Idle Air Control (IAC) DTCs
No EGR DTCs
Vehicle speed is less than or equal to 1 MPH
IAT is greater than -6.75°C but less than 75°C (167°F)
ECT is greater than 75°C but less than 117°C
Engine run time is greater than 6 minutes
Barometric Pressure (BARO) is at least 73 kPa
TP is less than 1.7%
Action Taken When the DTC Sets

The VCM will turn ON the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the MIL/DTC



The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.
A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).
Use the scan tool Clear Information function.
Disconnect the VCM battery feed for 30 seconds.
Diagnostic Aids

Difficulty running the OBD II status DTC P0420 test may be encountered in areas where the test conditions cannot be maintained easily, especially in urban areas.

Test Description

The numbers below refer to the step numbers in the diagnostic table.



This table includes checks for conditions that can cause the three-way catalytic converter efficiency to appear degraded. Inspect and repair exhaust system as necessary. Inspect the HO2S (Bank 1, Sensor 3 for the 5.0L) or (Bank 1, Sensor 2 for the 5.7L, 7.4L) pigtail and engine harness for any damage that can cause an intermittent fault in HO2S (Bank 1, Sensor 3 for the 5.0L) or (Bank 1, Sensor 2 for the 5.7L) circuits. Notice: In order to avoid damaging the replacement three-way catalytic converter, correct the engine misfire or mechanical fault before replacing the three-way catalytic converter.
If the three-way catalytic converter needs to be replaced, make sure that the following conditions are not present to caused the catalyst to be damaged:
Misfire
High engine oil consumption or coolant consumption
Retarded spark timing or weak spark.

Hey Skipr,
Is that from a manual?
which one?

O.K. been trying to use the noodle here. Let me know what you guys think.
I was thinking I could swap my post cat. o2 sensors. and if the code doesn't change banks hopefully the o2's are o.k. and odds are I have a rich lean condition that killed my cat. If so that could be the pre cat. o2 or bank one or injectors/ fuel delivery on bank one. or an exhaust leak. I am I barking up the right tree here of is there something I am over looking. I am thinking of buying the odb2 scanning software that will load on my home computer. Then I might be able to find the problem watching the sensor values right?

Thanks
Richard

Hey Skipr,
Is that from a manual?
which one?

That is from a 1998 C/K OEM manual (second revised edtion volume 3) There is a step by step troubleshooting chart if you want it, you can leave me a private message with your e-mail address. But understand the material in these OEM manuals is not for the DIY'er. Advanced knowledge is recommended. (1998 and 1997 are practically indentical as far as engine controls go).

I am about to start trouble shooting my code as soon as I get my scanner. Anticipating having to replace the cat I have read post on only using the stock replacement ones. But does anyone have any comments on these?

http://store.summitracing.com/default.asp?target=partdetail.asp&part=CTO-9333

Thanks
Richard