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Number77 Profile
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Date Registered: 09-2020
TOTAL POSTS: 8
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P0420 O2 Sensor


Sorry if this has been asked before. The engine light came on months ago and I bought an OBDII scanner to check what happened. And it showed P0420, Catalyst System Efficiency Below Threshold (Bank 1).

I replaced the upstream oxygen sensor, used liqui moly, changed spark plugs, started using 98 fuel and cleared the code. The light came back on after a 400 km. Then whenever I cleared it would come back on every 30 km.

Now I have checked the downstream sensor voltage and found that the voltage is acting like the upstream one going up and down which means something is wrong there. Best case scenario is that the downstream sensor is faulty that will only cost me $80 for a Bosch one. But is there a good chance the cat converter is not working properly and how do I test it? Anyone had the same problem before?

T30 2006 QR25DE

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Lister
X-5908
Perth
X-TRAIL ST-S T30 II Auto JUL 2006
15/Sep/2020, 9:22 am Link to this post Send Email PM   Send Private Message Blog
 
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Date Registered: 05-2017
TOTAL POSTS: 103
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Re:


Legally speaking, you cannot remove a catalyst without replacing it. Neither can an exhaust shop.

Note that the model before your car came with only one.

A mod is needed to stop the P0420 code if you do this as your ECU will expect a clean signal from a second sensor.

Wrecking yards with a new old previous model may have a previous model system you could buy to do a DIY fit.

NOTE: IANAL; Caution, This is only info for someone driving their T30 away from public roads.

---
05 T30 ST-X Auto
205/75x16 A/Ts on 6.5" ET40
200k: Refreshed suspension,fuel, ignition & cooling systems
Often good & dirty as is lifted 35mm on Sachs Automatics & poly bushings
Northern Sydney, NSW
15/Sep/2020, 6:42 pm Link to this post Send Email PM   Send Private Message Blog
 
Number77 Profile
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Date Registered: 09-2020
TOTAL POSTS: 8
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Re: Re:


Is it illegal because of the air pollution problem? I have zero knowledge on these things.

I looked up on google about "Mods" and found people putting a spark plug anti fouler in with the o2 sensor. That sounds like not actually fixing the problem but look the other way while disabling the engine warning light. Apparently it is not a proper fix but is that illegal too?

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Lister
X-5908
Perth
X-TRAIL ST-S T30 II Auto JUL 2006
15/Sep/2020, 9:54 pm Link to this post Send Email PM   Send Private Message Blog
 
Revhead Kev Profile
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Date Registered: 10-2006
Location: Mona Vale, Sydney, AUSTRALIA
TOTAL POSTS: 6360
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Re: P0420 O2 Sensor


The only way I know to test a cat converter is to have the exhaust gas analyzed. A tuning place with a dynamometer would be able to do that for you but could cost as much as a new cat converter.

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Kev X450(c) T30 Guru
03 Titanium Ti T30 Series 1 **MODIFIED**
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16/Sep/2020, 8:06 am Link to this post Send Email PM   Send Private Message Blog
 
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Date Registered: 05-2017
TOTAL POSTS: 103
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Re: Anti-foulers?


An extension tube may prevent the sensor causing the code, but it depends on how far from normal the sensor's output is, so may only work for a while, or not at all.

Search for 'O2 sensor simulator' to see how to solve incorrect output electrically just as easily.

Previous series II production to yours was 100% legal with one converter only, but was unable to meet a later regulation without it (Cars are seldom made just for the Oz market, they are part of other RHD production runs so our regulations may not even be applicable). That said, once a model is complied here with a certain emissions system, you cannot lawfully modify it.

Previously produced X-eys ran better with only one converter, and managed not to create clouds of pollution or upset anyone. The second cat was just a kludge Nissan applied to the existing design to meet a stiffer emissions regulation. Bear in mind that cats should recess into the floorpan/engine compartment and be adequately heat shielded, and cooled- not just monitored for failure. A series II X-ey's second cat hangs very low, as Nissan cheaped out on exhausts from the beginning (using a aluminised/mild steel exhaust rear sections instead of full stainless for a car that burns ULP was foolish at best). But then, they couldn't meet later regulations without adding the additional cat. They should have optmised the design to use slimline cats, and made some room for it somewhere, but by then they had the T31 coming and put their effort on that instead. So they hung it off the bottom in the middle where every rock and protrusion (including speed humps) will hit it.

So enjoy your second cat if you still have it, and replace it if it fails, and replace its sensor if that fails, or kludge the sensor (if your cat is ok), or fit an electric kludge. An exhaust that doesn't have the second cat is the optimal solution (if using the car 'off road'), just don't expect someone to remove it or kludge it for for you. Hmm. 'nuff said?

---
05 T30 ST-X Auto
205/75x16 A/Ts on 6.5" ET40
200k: Refreshed suspension,fuel, ignition & cooling systems
Often good & dirty as is lifted 35mm on Sachs Automatics & poly bushings
Northern Sydney, NSW
16/Sep/2020, 8:11 am Link to this post Send Email PM   Send Private Message Blog
 
Number77 Profile
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Date Registered: 09-2020
TOTAL POSTS: 8
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Re: Anti-foulers?


I need to check my car see if there is a second cat when I get home. I doubt it tho.

I just ordered a $80 downstream oxygen sensor it will come in two weeks time. By then I will just wait and I hope that will fix it.

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Lister
X-5908
Perth
X-TRAIL ST-S T30 II Auto JUL 2006
17/Sep/2020, 7:48 pm Link to this post Send Email PM   Send Private Message Blog
 
TopGun65 Profile
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Date Registered: 07-2015
TOTAL POSTS: 209
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Re: P0420 O2 Sensor


I tried the extension tube on mine, but the code P0139 which was "sensor circuit slow response" kept coming up even more often than the P0420 code.

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Eric
X-4282 (c)
Glen Alpine, Sydney
2010 T31 Cvt STL
18/Sep/2020, 5:10 pm Link to this post Send Email PM   Send Private Message Blog
 


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