This is pertaining to my 1999 GMC Suburban SLT with the 5.7L 350.
It has 144,000 miles and for the most part is all original.
I have a code P0430 which is catalyst efficiency below threshold Bank 2

From reading on line and stuff I have found out that there are 3 causes to this code:
1.) Exhaust Leak- I know my truck has no exhaust leak
2.) Bad O2 sensor- How do I determine?
3.) Bad CAT- How do I determine?

I have some live data so I'll post that up too.

Rich-LN Thresh
Meas: 0.445 (V)

LN-Rich
Meas: 0.445 (V)

Lo V for switch
Meas: 0.295 (V)

Hi V for Switch
Meas: 0.595 (V)

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Clay
1997.2 40th SLE-138k
1968 Bonneville 400ci w/TH-400-40k
1999 GMC Suburban SLT-191k
2005 Escalade 253k-GINA

It's my understanding that to check the function of the catalytic converter properly, you must analyze the gases before and after the cat. Most shops seem to agree that if the vehicle has always run with normal emissions, the cat should be fine for the normal life of the car.

O2 sensors can be tested with a voltmeter. If they are capable of switching at least once every 3 seconds (normally 1/second I think), they are probably working normally. An additional test is to goose the throttle and observe the O2 data. If it shows momentarily rich for 3-5 seconds, then momentarily lean for 3-5 seconds, and it responded immediately to the goosing, it's fine.

Reference:
http://repairnet.aircare.ca/manuals/ACE ... 100101.pdf

When I ask about how to test the converter in the past I was told that you should read a difference in temperature from the incoming gases at the converter to the gases leaving the converter. This can only be tested after the converter has been heated up. You can test this with a infrared thermometer, but first you should get the truck on the hwy for about a 30 min ride then test the temps at both ends of the converter with the truck running as soon as you stop... right at the inlet and outlet of the converter. If the temperature is the same at both ends it is said to be bad. When I checked this on my truck I was somewhere around 100-150 degs different on the outlet gas temp from what was coming into the converter. IIRC the temp readings were somewhere in the 400-500 deg range.

When the converter on my 95 Bonnie went bad I was reading high levels of HC on the emissions test. After having it replaced I found that the converter was broke up inside. And when you would smack the converter is would rattle too.

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2002 Buick Lesabre Custom L36 Titanium Blue Metallic/Medium Gray Cloth
2004 Buick Lesabre Custom L36 White/Graphite Gray Cloth
2015 SS Roof, Spare & 6M 6.2L LS3 415HP/415TQ SLIHRM/Jet Black Leather-Red Stitching
2010 Silverado LTZ Crew 4x4 6.2L L9H 417HP/403TQ NHT Black Granite Metallic/Ebony Leather
2013 Enclave Premium AWD 3.6L LLT White Diamond Tricoat/Cocoa Leather
2001 Wellcraft Martinique 2400 Merc 5.7L BIII 327hrs

1995 Bonneville SSE L36 Dark Polo Green Metallic **R.I.P. 4/28/10 236,400 miles**

If you stick your scanner back on to measure live data, can you see both O2 sensors show rich when you goose the accelerator? I'd have to check mine too, to see how it responds, but I'd expect both O2 sensors to go momentarily rich when goosing the throttle.

The upsrtream O2 sensor should switch betwen about 0.8 to 0.2V, the downstream should read lean and not switch if the cat is working normally. If both O2 sensors are switching, then I'd think that your cat is probably not working or you have an exhaust leak upstream somewhere.

Also the Suburbans have 2 cats so that makes it a little more difficult but usually if one is bad you just replace them both anyways

_________________
Clay
1997.2 40th SLE-138k
1968 Bonneville 400ci w/TH-400-40k
1999 GMC Suburban SLT-191k
2005 Escalade 253k-GINA