1997 GMC SAFARI P0420 TEST $ 02 TEST $ 07

This has a 4.3L single exhaust engine with 4 HO2S. I am pretty sure that the catalytic converter needs to be replaced since the post cat O2 sensor graph nearly mirrors the pre cat one and ranges from 0.15v to 0.79v. After the CEL came on I scanned the system and found only the P0420 bank 1 catalyst efficiency below threshold DTC. In reviewing the diagnostic data there are a couple of other problems indicated, but I don't know what they mean. Under the O2 Monitor section the following tests appear to be out of spec for both the B1S1 and B2S1 sensors:

Test ID $70
MAX: 255
MEAS: 255
MIN: 50
MOD: $10

Test ID $71
MAX: 255
MEAS: 255
MIN: 50
MOD: $10

All of the other O2 Monitor test results appear to be OK.

Under the Diagnostic Monitor there are also several IDs under TEST $ 02 AND TEST $ 07 that report as either HI or LOW:

Diagnostic Monitor
Data

TEST $ 02

ID: 46
MAX: ----
MEAS: 0
MIN: 64
STS: LOW
MOD: $10


TEST $ 07

ID: 0C
MAX: 0
MEAS: 8000
MIN: ----
STS: HI
MOD: $10

ID: 0D
MAX: 9b
MEAS: f8af
MIN: ----
STS: HI
MOD: $10

I have been unsuccessful in finding any information on these tests and IDs. Does anyone have any idea where I can find this information? I would just like to have a better understanding of what these tests mean - I still believe the CAT needs to be replaced.

On that note, any suggestions on what brand of CAT I should go for? I have been looking at Walker, MagnaFlow, and Maremont that range from $330 to $415. I read somewhere that some have had the same code come on after changing out the CAT because the brand wasn't as efficient as the OEM one. Should I be considering an OEM CAT?

Thanks for any advice.

I wouldn't worry about running any tests until you establish what codes other than 0420 you have. As far as an OEM cat, OEM would certainly be a high quality one, but we often use walker aftermarket cats. Others may have a different opinion, but we've never had a problem, but we never buy a universal cat, we use a direct replacement.

Cut the signal wire on the post cat O2 sensor and put a 1-megohm resistor inline <--- $.99 for a pack of 5 at radio shack... tricks computer into thinking cat is doing its job

The only code I have is P0420. I noticed the other test results in the download I did from the scantool - any idea where I can find out what they mean? On the CAT, I was considering a Walker direct replacement.





This may be an option if the CAT is being reported as marginal, but tailpipe test shows OK - don't have to pass inspection here yet.

Thanks for the feedback guys.

Does anyone know if either the factory service manual or one of the online subscription sites would have info for Test ID $ 70 & $71 under the O2 sensor monitor (Mode $05)? I believe these may be manufacturer specific tests.

I don't mind spending the money on the service manual or the on line services - I just don't want to waste the money if the info isn't there.

Thanks again for any help you can give me.

Mode 6 data is available here. http://www.acdelcotechconnect.com/

Thanks for the link. A couple of the test ids I am looking for were listed. Also went ahead and ordered the service manual.