Getting a P0420 on my 2001 Maxima SE. Did the whole research of possible causes.
Bad Pre-cat, Bad O2 sensors, Leak in Bank 1, etc....

Living in Massachuetts, we are required to use CARB complaint parts (legal in California parts). What would happen if I used a Non-CARB complaint part. Will my car pass inspection?

 

Also, I haven't been able to find a CARB compliant Bank1 Pre-Cat on the web. Trying to avoid having to buy Genuine Nissan Parts.

 

I'm assuming you will be installing a part which will remove the SES light, is this correct?

A lit SES light will end your inspection right there. Also, I'm assuming they will scan your car to double-check for any past SES lights. You need to make sure you reset the ECU after fixing your SES light problem.

Once you have the SES light fixed, then you will likely pass even without a non CARB part. For them to double-check the part they would have to get under the car and check the part physically and even then, they would likely not know if it was CARB or not.

You can pass a smog inspection without a factory pre-cat, even without a pre-cat at all, as long as you warm up the car prior to smogging.

 

Yes, that is correct.
Will erasing the P0420 code with a scan tool be enough to reset the ECU?
Good advice. Thanks.

 

The only way to really fix the P0420 is to replace the corresponding pre-cat. There are other ways to cheat but I am thinking you do not want that.

In Mass, if the light is on, your are automatically failed. If you erase the light and the monitors are incomplete, you do not pass. It gets even more complicated but let us just say that when you go for inspection, you really want to know that you will pass it before going there. Hook it up to a scanner which can tell you which inspection monitors are completed. I believe for MY2001, you can have maximum of one incomplete and still pass. Don't go to inspection station if you have more than one incomplete as shown by the scanner. You will fail but then to pass you will need to have your cat efficiency test to be completed. That is one of the most difficult one to pass and if things are not right, it will throw the light and you will be back to square one.

If you reset the light and time your visit such that all but one monitors are complete, you will get the sticker but it is difficult to achieve. I have done it couple of times myself but if you don't have your own scanner hooked up to the car all the time, forget doing that way. I am from Mass.

- Vikas

 

I've been learning all this the hard way. I erased the P0420 thinking I could pull a fast one at the inspection, but got the big "R" instead for incomplete monitor readiness.
Right now, I'm still showing the Catalyst Monitor and the O2 Sensor Monitor as incomplete.
What a pain in the butt!

Also, since you're from Mass., any advice on Non-CARB pre-cats? OK to use?

 

I know this sounds strange, but I got the same code on my 2003 3.5 Altima, worried like crazy I was having the precat problem. I reset the code with a cheap ebay code reader and put a bottle of Seafoam in my tank when it was only half full, the code stayed off for 1000 miles then showed up again.

I reset it, put another bottle of Seafoam and switched from Chevron Supreme to Shell Premium gas. The code did not come back on again for 2000 miles. At that point I put a tank of Chevron Spreme in, and 200 miles later the code came back.

I switched back to Shell Premium, and a tankfull later the code went out on its own, I did not reset it!

So before spending a lot of money (precats are $1000) try switching to Shell Premium and maybe use a can of Seafoa, see what happens.

Now if your precats have imploded (fairly rare in 3.5VQ) you have serious issues that could get blow-back debris into your combustion chambers and that ruins the motor...

 

With that "R" sticker, now you will definitely need new pre-cats because the cat monitor is not going to complete. If the only monitor is the cat one, you are now hosed because you already got the rejection. If that was the only incomplete monitor *before* getting the rejection, you would have passed. If you have led very charmed life and you get the cat monitor complete, run to the inspection station and get your sticker.

I don't think anybody would care if you have CARB approved pre-cat or not. I do not know how much is the price difference. Make sure you do change the correct one unless you are prepared to change both. If it is non-CARB, it will not last. I have heard as less as 6 months before the light coming on with aftermarket cats / pre-cats. Whoever puts the pre-cat, request them NOT to reset the light

- Vikas

 

Ok, I'll see what happens to the monitors. If it doesn't work out, I'll just change the bank 1 pre-cat. Thanks for the advice.

 

Replacing the precat was the only thing that fixed my P0420 code.

 

Generally, when you drive on the freeway over 55 miles on hour for few minutes and then let it coast for a while, the cat monitor test is run (assuming all other conditions such as coolant temperature etc are satisfied). If you replace the the pre-cat, then don't reset the light because that will clear all the monitors. Just try to get the engine to run the cat monitor test. That way you will know quickly if the pre-cat fixed it or not and also you can drive to the inspection station and get the sticker quickly.

 

Here's the latest news. Check engine light is back on. Catalyst Monitor is now complete (OK). O2 Sensor monitor remains incomplete. Still getting the P0420. Does this mean changing the Bank1 O2 sensors will fix this problem? They are still the original sensors with 150000 miles on them. All this time, the car drives like there is nothing wrong with it.

I also retreived a bunch of data from my scan tool. Anyone know how to decipher them?
Out of a bunch, these are the only 2 that show "FAIL". I will continue to research this on the web. Thanks in advance!
Test $01 Data
ID: 01
MOD: $10
MEAS: 85
MAX: 64
MIN: ----
STS: FAIL

Test $02 Data
ID: 01
MOD: $10
MEAS: A
MAX: ----
MIN: 26
STS: FAIL

 

I came across this article. Helped me understand some of this Mode $06 Data.
http://d-tips.com/general/articles/article.aspx?id=5

 

Have you put the new pre-cats or not? If you changed them, did you get the OEM or aftermarket? Are you sure you changed the right bank pre-cat? O2 sensors are only the messengers. Don't shoot them :-)

 

TEST VALUE AND TEST LIMIT (GST ONLY — NOT APPLICABLE TO CONSULT-II)

The following is the information specified in Mode 6 of SAE J1979.
The test value is a parameter used to determine whether a system/circuit diagnostic test is “OK” or “NG” while being monitored by the ECM during self-diagnosis. The test limit is a reference value which is specified as the maximum or minimum value and is compared with the test value being monitored. Items for which these data (test value and test limit) are displayed are the same as SRT code items. These data (test value and test limit) are specified by Test ID (TID) and Component ID (CID) and can be displayed on the GST screen.


SRT item Self-diagnostic test item DTC
Test value
(GST display) Test limit Conversion
TID CID
CATALYST
Three way catalyst function (Bank 1)
P0420 01H 01H Max. 1/128
P0420 02H 81H Min. 1
Three way catalyst function (Bank 2)
P0430 03H 02H Max. 1/128
P0430 04H 82H Min. 1
EVAP SYSTEM
EVAP control system (Small leak)
P0440 05H 03H Max. 1/128mm2
P1440 05H 03H Max. 1/128mm2
EVAP control system purge flow monitoring P1447 06H 83H Min. 20mV
HO2S
Heated oxygen sensor 1 (Bank 1)
P0133 09H 04H Max. 10ms
P0131 0AH 84H Min. 10mV
P0130 0BH 04H Max. 10mV
P0132 0CH 04H Max. 10mV
P0134 0DH 04H Max. 1s
Heated oxygen sensor 1 (Bank 2)
P0153 11H 05H Max. 10ms
P0151 12H 85H Min. 10mV
P0150 13H 05H Max. 10mV
P0152 14H 05H Max. 10mV
P0154 15H 05H Max. 1s
Heated oxygen sensor 2 (Bank 1)
P0139 19H 86H Min. 10mV/500ms
P0137 1AH 86H Min. 10mV
P0140 1BH 06H Max. 10mV
P0138 1CH 06H Max. 10mV
Heated oxygen sensor 2 (Bank 2)
P0159 21H 87H Min. 10mV/500ms
P0157 22H 87H Min. 10mV
P0160 23H 07H Max. 10mV
P0158 24H 07H Max. 10mV
HO2S HTR
Heated oxygen sensor 1 heater (Bank 1)
P0135 29H 08H Max. 20mV
P0135 2AH 88H Min. 20mV
Heated oxygen sensor 1 heater (Bank 2)
P0155 2BH 09H Max. 20mV
P0155 2CH 89H Min. 20mV
Heated oxygen sensor 2 heater (Bank 1)
P0141 2DH 0AH Max. 20mV
P0141 2EH 8AH Min. 20mV
Heated oxygen sensor 2 heater (Bank 2)
P0161 2FH 0BH Max. 20mV
P0161 30H 8BH Min. 20mV
EGR SYSTEM EGR function
P0400 31H 8CH Min. 1
P0400 32H 8CH Min. 1
P0400 33H 8CH Min. 1
P0400 34H 8CH Min. 1
P1402 35H 0CH Max. 1

 

It is telling you that your "Three way catalyst function (Bank 1)" failed both tests. Test $01 has max allowed value of 64 (I am not sure if your scanner is reporting decimal or hexadecimal values) but the actual measured value is 85. Similarly test $02 has minimum required value of 26 but actual was A (decimal 10), so that test failed. Also look at the data for Test $03 and $04 which is for the other bank. I suspect those numbers are going to be on the borderline too. Your cat monitor test completed but it resulted in failure. Also once that fails, the ECM will not try to run further tests.

I really appreciate your tenacity and you not going the o2 extender route but I suspect you would have been better of if you had thought this thing over before hand. With that big "R" sticker on your vehicle now, your options are limited as the inspection station would be more stringent during the re-inspection.

As you can infer, this is my specialty and I had to learn it old fashioned way :-(

- Vikas

 

I haven't done any repairs to my car yet. Still investigating this whole thing. One mechanic wanted over $2000 to replace both pre-cats using nissan parts. I asked about aftermarket pre-cats and he said he didn't recommend them. The car itself is worth less than that.

Thanks for all the info.

 

You only need the pre-cats and those should not be $2K!

You can try G2P (Guaranteed to Pass) from Amazon. It is made by CRC industries and they don't make junk. http://www.amazon.com/gp/product/B00...=ATVPDKIKX0DER

Or try Cataclean from Amazon; this might be snake oil; but you can be the first one to gamble $25.

Or go for the O2 extender.

- Vikas

 

That includes labour as well. He suggested changing both pre-cats, but I'll stick to bank1 only (and pray nothing else disintegrates during the removal process). Went to another mechanic today and he also did not recommend aftermarket cats. Said he's seen it a hundred times where it will solve the problem for about six months but the CEL will return. He seemed pretty honest. It looks like a new Nissan Bank1 Pre-Cat is the most likely scenario. Not sure about those additives. I'll research it. Thanks again.

 

Would the O2 extender go on the upstream or downstream sensor?

 

Come on! I thought you have been doing your research on this! (sorry about that but it was just a slight humor in a bad taste :-)

Extender *ALWAYS* goes on the downstream sensor.

If you are going to do it, try to get a stainless one from ebay. Get two and do both. Otherwise if you did the wrong bank, you would be really really mad. Don't ask me how I know that :-)

This is what I will suggest and I hope I have enough credibility to give you this advice.

1) Order the couple of stainless ones (if you can still find them on ebay) $30 Regulars one will run you about $16 for two. If no stainless, settle for plain old steel. They work but start looking pretty nasty cosmetically in few months.
2) Grab the G2P from Amazon ($11) or locally ($16)

Since you have only until the end of the month to get this sorted, start both the processes in parallel.

Follow the directions on that can. I presume you have easy access to a scanner. If the G2P works, get the car inspected and then have one of your trusted mechanic do the extenders. It is lot more easier when the car is on the lift for an oil change. Slip a twenty or so to him. Tell him to spray Kroil or PB blaster as soon as the car is on the lift and after the oil change, he should be able to loosen the original downstream sensors. Count the number of turns and make sure when it is all done that you have not twisted the wires. You will need couple of tie-wraps to re-route the wires.

If you are good at working on your back when the car is on the jack stands, you can do this yourself. Since I have found a trustworthy mechanic, I usually don't get my hands dirty.

- Vikas

 

AAAAAAAAAAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHH HH!
CAN NISSAN MAKE AN ANYMORE DIY UNFRIENDLY CAR!!! DAGNABBIT!!!

I managed to loosen the bank1 downstream O2 sensor. Followed the wire to its electrical connector. The connector is located on a connector bracket which is right in front of the engine. A row of four connectors on the top bracket and a row of four connectors on the bottom bracket. Looking at my replacement O2 sensor, there is a plastic clip which needs to be pressed (I'm assuming) in order to release the O2 electrical connector. Now how in the hell is anyone supposed to reach this clip when it's on the side facing the engine!!! &^%#*!!! Impossible to get a finger in there. Tried a screwdriver without success. You would think the brillant engineers at Nissan would have placed the release clip facing the radiator where there is plenty of room to press it.

Anyone manage to do this? If not, I will be exchanging the Bosch O2 sensor for a Bosch sensor with OE Smartlink and just splice it into the old wiring.

 

I know this thread is kind of old but replace that O2 sensor is fairly easy all i 7/8 spanner to loosen the 02 sensor after spraying it with WD-40 about 5 or 6 hours before. I started my unplugging the corresponding connect at the top front of the engine(dp this from the top not the bottom. Then got down under the car and loosened the o2 sensor and put the new one in right after. I think followed the wire up removing the old sensor with clips and putting the new ones in as i went. I found this to be easier for mes so i wouldnt loose sight of the holes for the plastic clips. The only tools i used was needle nose pliers and a flat heard screwdriver to remove clips. Dont get me wrong I broke a few of the old clips to get them out but he** I was throwing the old one anyway. the only plastic clip i replaced from the top was the one right before the electrical connector. all clips can be reached without removing other parts you have a little patience