Suburban Self-Tests Failed or Not Completed

nGAbear · June 4, 2012

Running OBDCOM software to monitor my 2001 Suburban in hopes of isolating my P0420 error and notice that there is a field in the program labeled " Self-Tests Failed or Not Completed". In this field is a list of three items:

Catalyst

Evaporative System

Oxygen Sensor

I have four new oxygen sensors on order for delivery Wed. My thinking is that I can swap them out and see what it does to this code. The age, mileage and relatively unknown history of this truck should be enough for me to swap them out, regardless. Am I correct in my thinking that this could be a good first step in resolving this code? If I swap them out and the code persists then chances are the cat is bad, correct?

** EDIT: I just canceled my o2 sensor order until I hear what you think.

The part that throws me is the second item in that list above "Evap system". On a 2001 Suburban, is an EVAP canister independantly monitored or is one of the other two items in that list responsible for keeping tabs on the EVAP canister-- so naturally when the part responsible for the monitoring fails, so does the testing/monitoring of the EVAP canister?

Do you think I am correct in my approach here or am I off course?

jimlem · June 5, 2012

Running OBDCOM software to monitor my 2001 Suburban in hopes of isolating my P0420 error and notice that there is a field in the program labeled " Self-Tests Failed or Not Completed". In this field is a list of three items:

Catalyst

Evaporative System

Oxygen Sensor

I have four new oxygen sensors on order for delivery Wed. My thinking is that I can swap them out and see what it does to this code. The age, mileage and relatively unknown history of this truck should be enough for me to swap them out, regardless. Am I correct in my thinking that this could be a good first step in resolving this code? If I swap them out and the code persists then chances are the cat is bad, correct?

** EDIT: I just canceled my o2 sensor order until I hear what you think.

The part that throws me is the second item in that list above "Evap system". On a 2001 Suburban, is an EVAP canister independantly monitored or is one of the other two items in that list responsible for keeping tabs on the EVAP canister-- so naturally when the part responsible for the monitoring fails, so does the testing/monitoring of the EVAP canister?

Do you think I am correct in my approach here or am I off course?

The 3 systems you listed are part of a set of self-tests that run automatically each time you start up. And I believe I read once (a long while back) that they are separate systems/tests including the evap canister and related parts. It's one of the biggies in those tests I believe. As I read it they and their related tests are separated and self monitored by the related system, only. E.g. the evap system monitors itself and the O2 sensors monitor themselves and for these self tests that run in the PCM, before the engine is run or the truck driven, they do not affect the other systems nor get monitored by any other system. Now, after engine is running, the PCM monitors the interaction between all those systems any one with a problem could likely cause errors across several related systems. IE a bad O2 sensor causing mixture issues or bad MAF sensor causing a misfire. But for the sake of just those self-tests that show ready or not ready, they are quick and specific unto themselves. With the correct reader, you can force those same systems to run a set of self tests individually on each system one at a time, while the truck is running/driving. I'm not sure if it runs the same test on them but I think not. While running, the self tests seem more in-depth and run a bit longer than that quick pre-start test. The interesting thing is that those systems have those built in tests to run at all. Most stuff you just monitor and look up in a book if the numbers in the results are normal or bad or within range etc. Or, you wait for a CEL from the PCM to tell you there's an issue, but these certain key systems have hard-coded tests in the PCM to actively yank their chain and see how they squawk.

Back to the self tests at start-up: the PCM has a set of semi complex lists of number of "good starts" ie when a test completes w/o errors, these balance out with number of miles and or time spent running at various speeds, loads and throttle positions, since the last CEL. Some incorporate temperature and other factors as well. Anytime you get a DTC for one of those items or even when your battery dies (or you disconnect it for working on the truck), these parameters get reset and you have to start over with their countdowns. I've noticed driving around town, short distances like running a few errands, it can take a week or so for all to go to a normal or "ready" state. If you can spend an hour or so on and off the highway and vary the conditions, most will reset shortly after (if their are no further issues causing new faults). Many state smog checks are now reading this parameter first thing upon starting your test and if it says "not ready" they tell you to go drive it as I said above and bring it back in a day or so. CA at least, now requires this self-test pass to continue further into the actual "rolling-road"/ smog machine tests. If you have a bad O2 sensor, it can keep this permanently in the not-ready state until replaced, the DTC cleared, and the self tests completed. I had an intermittent O2 issue that would pop up maybe once a week, then go away for a week, and so on. It kept it in the not-ready condition for a month until I finally got it all fixed. Hope this helps as it's the total extent of my knowledge on it but if you need further, I sure someone else will chime in and explain further. Good luck.

I saw your earlier posts about the purchase, BTW. Bad luck and a pisser I know but it sounds like you've handled the refurbishment of the truck real well. I have a feeling you'll end up with a Sub you really love and can trust because you personally laid hands on all its parts and will know it inside and out very, very well. Hang in there.

Jim

p.s. You were asking about the air-ride system I think in another post? I don't have that system but spent an hour plus on the forums about 5-6 weeks ago when an old post got bumped up by a guy trying to find out about ways of getting rid of the system or adding a resistor to stop CELs when the OEM units are replaced by resistors or other means. It was VERY interesting reading. Several later posters all had good info on name brand aftermarket kits allowing regular shocks and came with whatever was needed to safely and correctly bypass the OEM warning system when no air ride parts are installed. I learned a lot and it was good info for anyone to soak up. Just search for post about bypass air-ride or replace air-ride with aftermarket shocks. You'll get a ton of GREAT reading plus some scams to watch out for (like guys selling $0.37 Radio Shack resistors as a $50 kit (and they never really work correctly) So again. good luck and I hope I was some help to someone for once. Post some pics too as you do these things, I would like to see it get whipped into shape.

jBlaze3000 · June 5, 2012

I saw your earlier posts about the purchase, BTW. Bad luck and a pisser I know but it sounds like you've handled the refurbishment of the truck real well. I have a feeling you'll end up with a Sub you really love and can trust because you personally laid hands on all its parts and will know it inside and out very, very well.

I was going to say the same thing. Before I bought my Suburban I almost went with a Durango, just because it was identical under the hood to my old Dodge Dakota. I turned just about every bolt on that truck and knew it like the back of my hand. In the end we decided we liked the Suburban's the best, and I'm looking forward to getting to know this truck...

nGAbear · June 5, 2012

The 3 systems you listed are part of a set of self-tests that run automatically each time you start up...

Thank you for explaining this. So to recap and make sure I understand this the way that you explained it, with the list of three items I layed out earlier, it may be that I might not have put enough miles on the vehicle for those items to be 'cleared'. Here in Georgia we have a similiar emission law/SOP (although something tells me it isn't as stringent as the law in CA) regarding what I knew as 'necessare milage after emissions work'. --if that even made sense...

Last night I went ahead and ordered four new o2 sensors. I'm just going to start there as I told earlier. Again, the way I see it is with the age, milage and unknown history of this truck it will be good to establish a known 'base' to operate from. I also have new OEM rotors and EBC Green Stuff 6000 series pads for the rear on order for today's delivery.

...I turned just about every bolt on that truck and knew it like the back of my hand. In the end we decided we liked the Suburban's the best, and I'm looking forward to getting to know this truck...

That is exactly how I am beginning to feel about this one. That is the silver lining that I am holding on to. I just over-paid for my truck in the end.

Guys, thank you for your help and insights. When I first began posting here someone said that there were some good eggs on this site; I have to agree.

Chris · June 6, 2012

I had my cat checked out today. i have the same P0420 code. my issue is the cat and the tech said most the time that code means the left cat is shot

nGAbear · June 6, 2012

Super. Thanks for the heads-up.

You mind if I ask what they charged you to check out the cat?

Chris · June 6, 2012

They didn't charge me anything. I was surprised. And because I'm still in California I have to get some off the shelf brand I haven't heard of

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gmtech4 · June 7, 2012

the bottom diag tree comes out bad for some reason,top part is code info,,

try not to throw parts at the truck,the money can pay for actual diagnoses from a technician/shop

DTC P0420 or P0430

Circuit Description

In order to maintain low emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), the engine controls system uses a 3-way catalytic converter. The catalyst within the converter promotes a chemical reaction, which oxidizes the HC and CO that are present in the exhaust gas. This reaction converts these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx which converts into nitrogen. The powertrain control module (PCM) monitors this process using Bank?1 of the HO2S?2, which is located in the exhaust stream past the 3-way catalytic converter. Bank?1 of the HO2S?2 produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalyst's ability to effectively convert the exhaust emissions. If the catalyst is functioning correctly, the Bank?1 of the HO2S?2 signal will be far less active than the signal that is produced by Bank?1 of the HO2S?1. This indicates that the 3-way catalytic converter's oxygen storage capacity is below an acceptable threshold.

The PCM performs this diagnostic test at idle. When the conditions for running this DTC are met, the following occurs:

1. The PCM captures the current rear HO2S rich-to-lean status.

2. The air-to-fuel ratio transitions from rich to lean or from lean to rich, depending on the capture rear HO2S rich-to-lean status.

3. The air-to-fuel ratio transitions a second time opposite the first air-to-fuel ratio transition.

4. The PCM captures the response time of the front and rear heated oxygen sensors when the air-to-fuel ratio transitions occur. The HO2S response time goes from less 300?mV to more than 600?mV, and from more than 600?mV to less than 300?mV.

5. The PCM measures the time it takes the rear HO2S voltage to cross a reference rich-to-lean threshold, minus the time it takes the front HO2S voltage to cross the same rich-to-lean threshold. The difference between the front HO2S time and the rear HO2S time is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.

Conditions for Running the DTC

• DTCs P0101–P0103, P0106–P0108, P0112, P0113, P0117, P0118, P0125, P0131–P0135, P0137, P0138, P0140, P0141, P0151–P0155, P0157, P0158, P0160, P0161, P0171, P0172, P0174, P0175, P0200, P0300, P0325, P0327, P0335, 336, P0341–P0343, P0351–P0358, P0443, P0446, P0449, P0502, P0503, P0506, P0507, P1120, P1125, P1133, P1134, P1153, P1154, P1220, P1221, P1275, P1276, P1280, P1281, P1285, P1286, P1441, P1514, P1515, P1516, P1517, or P1518 are not set.

• The intake air temperature (IAT) is more than –15°C (+5°F), but less than 75°C (167°F).

• The barometric pressure (BARO) is more than 74?kPa (10.7?psi).

• The engine is operating.

• The engine coolant temperature (ECT) is more than 70°C?(158°F), but less than 120°C (248°F).

• Since the end of the last idle period, the engine speed is more than 900?RPM for a minimum of:

- 20?seconds for manual transmissions

- 30?seconds for automatic transmissions

• The closed loop fuel control is enabled.

Conditions for Setting the DTC

The PCM determines if oxygen storage capability of the catalytic converter has degraded to less than a calibrated threshold.

Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

• The control module turns OFF the malfunction indicator lamp (MIL) after 3?consecutive ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC clears after 40?consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.

Test Description

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

4 Before you replace the 3-way catalytic converter, correct any conditions which may have damaged the catalyst.

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check–Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Are any other DTCs set?

Go to the applicable DTC table

Go to Step 3

3

Check for the following conditions:

Verify that the 3-way catalytic converter is an original equipment part.

Inspect the 3-way catalytic converter for damage from the following conditions:

- Dents

- Severe discoloration caused by excessive temperatures

- Holes

- Other conditions

Verify that an internal 3-way catalytic converter rattle that is caused by a damaged catalyst is not present.

Inspect the exhaust system for the following conditions:

• Leaks

• Damage

• Loose hardware

• Missing hardware—Refer to

Exhaust Leakage in Engine Exhaust.

Verify that the HO2S?1 and the HO2S?2 are secure, and ensure that the pigtails and the wiring are not damaged or contacting the exhaust.

Did you find and correct the condition?

Go to Step 5

Go to Step 4

<a href="http://gsi.xw.gm.com/newsi/showDoc.do?docSyskey=663257&cellId=30546&pubObjSyskey=2902567&from=sm&pubCellSyskey=1269004&deliveryEffectiveDate=Jun+1%2C+2012#td04">4

Replace the catalytic converter. Refer to Catalytic Converter Replacement in Engine Exhaust.

Did you complete the replacement?

Go to Step 5

—

5

1. Use the scan tool in order to clear the DTCs.

2. Turn OFF the ignition for 30?seconds.

3. Start the engine.

4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 6

Go to Step 2

6

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK

nGAbear · June 7, 2012

Rob, wow; thank you!

Chris · June 7, 2012

My P0420 was the cat. Had it changed no more code truck has more pep. The inside of the cat was in pieces

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nGAbear · June 10, 2012

Two days ago I cleared the error code and crawled under my beast and replaced all four o2 sensors (also replaced my rear rotors and brake pads).

I'm happy to report that 700 miles later and no error code as well as more pep and responsiveness!

Edit: When trying to remove the old downstream sensors, it took quite a bit of penetrating oil and some serious mannin-up to remove the old rusted nuts. At one point when working on the passenger side rear sensor (I replaced these without the use of jack stands) I was pulling straight down towards my face and with a chuckle realized that I was about to punch myself in the face if I kept that up...so I decided to spray it with some more penetrating oil and give it a little more time to saturate.

txab · June 10, 2012

jBlaze3000 · June 12, 2012

Two days ago I cleared the error code and crawled under my beast and replaced all four o2 sensors (also replaced my rear rotors and brake pads).

I'm happy to report that 700 miles later and no error code as well as more pep and responsiveness!

Edit: When trying to remove the old downstream sensors, it took quite a bit of penetrating oil and some serious mannin-up to remove the old rusted nuts. At one point when working on the passenger side rear sensor (I replaced these without the use of jack stands) I was pulling straight down towards my face and with a chuckle realized that I was about to punch myself in the face if I kept that up...so I decided to spray it with some more penetrating oil and give it a little more time to saturate.

Just replaced the downstream drivers side sensor on my Suburban yesterday. Tried to get it out without jacking up the vehicle but realized pretty quick that wasn't going to happen. 1 jack, 1 pipe wrench, and 1 3-foot cheater bar later she was out! Piece of cake but unfortunately for me it didn't clear my error code.

Chris · June 12, 2012

Two days ago I cleared the error code and crawled under my beast and replaced all four o2 sensors (also replaced my rear rotors and brake pads).

I'm happy to report that 700 miles later and no error code as well as more pep and responsiveness!

Edit: When trying to remove the old downstream sensors, it took quite a bit of penetrating oil and some serious mannin-up to remove the old rusted nuts. At one point when working on the passenger side rear sensor (I replaced these without the use of jack stands) I was pulling straight down towards my face and with a chuckle realized that I was about to punch myself in the face if I kept that up...so I decided to spray it with some more penetrating oil and give it a little more time to saturate.

Just replaced the downstream drivers side sensor on my Suburban yesterday. Tried to get it out without jacking up the vehicle but realized pretty quick that wasn't going to happen. 1 jack, 1 pipe wrench, and 1 3-foot cheater bar later she was out! Piece of cake but unfortunately for me it didn't clear my error code.

If its not the sensor its the cat

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geoech1 · October 31, 2012

2007 GMC Sierra. Ok this is my problem. I went in for my emissions test and my data port didn't communicate with Pep Boys tester. I then checked with my scan tool and they were right. No lights or anything from the port. So i started checking fuses that dealt anything with the engine and anything else i didn't know what it controled. Then i looked and the check engine light was on and it said "engine power reduced" on the milage display. I checked the code and the scanner said it was from a data communication loss between the computer and engine. So now at least my port was working now. So i erased the code and went on a 150 mile drive cycle trip. And my truck is still not ready for the emissions test. Any suggestions on how to get a green light on my scan tool?