zippinbye

I'm trying to resolve DTCs P0420/P0430 (“Catalyst Efficiency Below Threshold” {Bank 1/Bank2}). The MIL is on. The following are also illuminated: VSC TRAC OFF, VSC OFF, and the slippery-vehicle symbol.

A bit of history: I changed the alternator due to failure. because of low-battery states, swaps and other power interruptions, there were numerous unintentional ECM resets. Shortly after installing the alternator, I got DTCs P0441 and P0455, ("EVAP Emission Control System Purge Flow Fault" and "EVAP Emission Control System Leak {Large}.” I tried a new fuel cap. Then the 420/430 codes came along – no more 441/455.

Today I cleared the 420/430 codes and tried to pass emissions testing. I forgot that my state (NV) now hooks-up to the OBD II, and they will never get to exhaust sampling if the OBD is not in order. I was rejected because the following were “not ready” according to their scan: OBD Catalyst, OBD Evap, OBD Sec Air, Oxy Sensor.

The primary questions: 1) Why would stability control faults accompany an emissions issue? To be clear, the stability info is only present on-dash, no codes; 2) How could I have two bad cats at exactly the same time, or two exhaust leaks (can't hear any) develop simultaneously, or opposing 02 sensors go bad in unison? And the coincidence to alternator work plus the immediate follow-on to a (seemingly) resolved evap issue is weird too! 3) Wouldn't I have additional, specific codes if I had one or more bad O2 sensors?

Any suggestions to further diagnose this issue would be appreciated.

zippinbye

Both catalysts show roughly equivalent temperatures when sampled with a laser thermometer, and the rise suggests they are working: pre-cat temp is about 300F, post-cat around 525F.

mann777

Zippin...what you have is that the Catalyst system efficiency is below the threshold on Bank 1 ( O2 Sensor before the catalyst ) and Bank 2 ( O2 Sensor after the catalyst ). This is detected and fault is recorded when the fuel ratio ie that the Rich/Lean compensation is alternating and detiorating. You get a MIL on the cluster. But there are various other conditions also to be checked, when you get a fault P420/P0430 such as Mass Air Flow Sensor, Engine Coolant Temp Sensor,Engine Speed Sensor, Intake Air Temp Sensor.
But the typical detioration comes from the O2 Sensors normally. You have posted the temp for Pre-Cat which is actually below the normal Threshold. Should read as 842 to 1526F ( both Pre for the Upstream Cats & Post Cats - Downstream Cats) .
Also check what is normal Engine Idle RPM reading after Engine heats up ons tart ( Reading to be taken after approx 3-5 minutes) That is when the O2 Waveform behave erratic if so they are beginning to deteriorate.

zippinbye

My posted temps were external laser shots, just to demonstrate rise across the catalyst, each shot at the cat's narrowing taper area, roughly in between exhaust tube diameter and max cat diameter.

I hooked up a more capable code reader, an Actron CP9180. Now I have OBD temps that show a 273 degree rise and are identical left/right: 892 vs. 619..

I'll add another post with more OBD #s. It will be lengthy, but hopefully the thread will evolve to a solution and at some point others can benefit from the information.

Mann 777, thanks once again for knowledgeable assistance, as you have kindly offered me in the past, as well as numerous others!

zippinbye

Here is some additional OBD information that may be of use. FYI, this freeze frame was taken in the same day that I cleared the DTCs with an Actron CP9180, shortly after a drive cycle re-triggered codes 420/430. Engine running, sustained idle @710 RPM, coolant 195 degrees, IAT 132 degrees, ambient air temp around 80 degrees.

Here are the O2 readings:

O2S12 V 0.740

O2S22 V 0.760

O2S11 V 3.254

(the display shows other information before the last sensor reading. In case it's meaningful, that is: EQ RATIO11 1.000, EQ RATIO21 0.997)

O2S21 V 3.249.

Catalyst temps: CAT TEMP11 892, CAT TEMP21 892, CAT TEMP12 619, CAT TEMP22 619 (not a type, left and right are identical temperatures).

I also have diagnostic system monitor test results, which I think I selected individually in real time, not freeze frame:

O2 Sensor B1S1 Test $8E Module $00 MAX: 19.898 V MEAS: 0.848 V MIN: 0.199 V

O2 Sensor B1S1 Test $91 Module $00 MAX: 151.011mA MEAS: 33.007mA MIN: 104.003 mA

O2 Sensor B1S2 Min V for Cycle Module $00 MAX: 0.195 V MEAS: 0.175 V MIN: 0.000

O2 Sensor B1S2 Max V for Cycle Module $00 MAX: 1.190 V MEAS: 0.722 V MIN: 0.605 V

O2 Sensor B1S2 Test $8F Module $00 MAX: 7.902 MEAS: 4.765 MIN: 0.000

O2 Sensor B2S1 Test $8E Module $00 MAX: 19.898 V MEAS: 0.862 V MIN: 0.199 V

O2 Sensor B2S1 Test $91 Module $00 MAX: 151.011mA MEAS: 43.007mA MIN: 104.003 mA

O2 Sensor B2S2 Min V for Cycle Module $00 MAX: 0.195 V MEAS: 0.117 V MIN: 0.000

O2 Sensor B2S2 Max V for Cycle Module $00 MAX: 1.190 V MEAS: 0.800 V MIN: 0.605 V

O2 Sensor B2S2 Test $8F Module $00 MAX: 7.902 MEAS: 13.437 MIN: 0.000

Catalyst B1 Test $A9 Module $00 MAX: 19.960 MEAS: 14.218 MIN: 19.921

Catalyst B2 Test $A9 Module $00 MAX: 19.960 MEAS: 8.046 MIN: 9.921

Thanks for taking the time to crunch all these numbers. Please let me know if there's any other info which would be useful.

zippinbye

Well, I'm definitely leaning toward 02 sensor replacement, given the present options. Should the downstream sensor be considerably less than the upstream? I'm finding the post-cat sensor for less, despite it being 4-wire heated. Seems opposite of what the price differential should be. But I have identified both plug and play Densos (OEM supplier) and a "universal" Desno for the post-cat. The one Denso I have found for precat is vaguely identified, not yet sure if it's a plug-in or requires wiring. Customer reviews and other sources swear the Densos are the identical sensor in universal form, it's just either with or without plug. The negative comments about the universal versions all have to do with wiring issues, including one gent who probably overheated the probe while soldering (crimp connection recommended, but he went the "extra mile").

I've got a Denso 234-4209 located on Amazon for $37.90. Said to be identical to OEM except it is universal in the sense it must be wired to existing plug. Comes with crimp connectors and shrink tubing for that purpose. The pre-cat Denso I have located is a 234-4209 for at least $110. Not yet verified, but it could be a direct plug in. Still trying to find a Denso that would require splicing, if the price difference commensurate like the post-cat. Since I am entering the realm of parts-changing without an absolute diagnosis, it's important to keep the cost down as long as the sensor is right. I don't mind the wiring.

Any comments on the universal Denso sensors, or a part # for the pre-cat that represents the universal version? I like the idea of a sub-$200 job for all 4 sensors as long as they are legit. Especially if I have to move onto replacing cats after that!