I have a 2001 Pathfinder LE which will not pass California emissions because the ODB II shows oxygen sensor not ready.
The smog guys said just drive it 50+ miles and it should go ready. It's been 500 miles and no change.
There are no codes stored in the ECM.
I tried disconnecting the battery to reset the ECM, but after another 300 miles, it still shows not ready.
Any ideas ?
Do I need to have my ECM replaced ?

That's CA smog for ya. There are 520897207037 hoops to jump through to get your car inspected. From a quick Google-machine search, sounds like you need to visit another place that will pass it?

http://workingreporter.com/wordpress/st ... heck-hell/

Most other states will pass it if the CEL isn't on (CEL on = current problem).

Yes CEL is not on. Sorry used the wrong acronym SES.

Thanks for the link. Wow what a rabbit hole.....

Now that I know what I'm looking for, I'll try some of the drive cycle instructions and check again.

Never heard of the O2 drive cycle not coming to completion, that can't be good.

Do you have a code reader? If so, try resetting your codes. Even if there are no codes stored, you still may be able to reset the system. If you don't have one, go to an auto parts store and have them do it.

Other possibilities may be disconnecting the battery, then disconnecting the ECU.

Relevant, though I don't see it described in the linked FSM:

post6555901.html

I'll try to track it down in the FSM tonight.

I suppose you could also disconnect your O2 sensors and see if the ECU throws a circuit disconnected code, then see if the cycle completes. I wonder if it's the sensor(s) throwing the ECU off, or the other way around.

atraudes wrote:Relevant, though I don't see it described in the linked FSM:

post6555901.html

I'll try to track it down in the FSM tonight.

Thanks, I found the Drive cycle on EC-67 of the FSM. I just completed it twice with no luck.

I'm going to try the disconnection of the Oxygen sensors to see if they throw the code assuming I can find them.

You can pass emmissions in WA state with one monitor not ready. Is this your only monitor thats not ready yet?

barnaclebob wrote:You can pass emmissions in WA state with one monitor not ready. Is this your only monitor thats not ready yet?

Yes, it is only the oxygen sensor. The others reported ready.

I think it is true in California too, but from the thread I read, the testing station are tracked and it counts against them so they won't do it.
I haven't looked around for another station that might pass with the not ready, but the one I did the original test at will not.

I disconnected each O2 sensor and got the expected codes. Reconnected and cleared the codes.
Now to do the Drive cycle again.....

It may be against the law for them to deny you. It would be in WA.

500 miles is way too long - 100 or 120 is the most you should expect, in the most extreme cases.

What scan tool are you using?

What kind of driving are you doing? You usually need a cold start or two, some 40-45mph cruising, some 65-70 mph cruisin. 60-80 miles should get all monitors ready, as long as you don't have any mechanical issues.

Have you ever messed with, or touched any of your O2 sensors?

fueler wrote:500 miles is way too long - 100 or 120 is the most you should expect, in the most extreme cases.

What scan tool are you using?

What kind of driving are you doing? You usually need a cold start or two, some 40-45mph cruising, some 65-70 mph cruisin. 60-80 miles should get all monitors ready, as long as you don't have any mechanical issues.

Have you ever messed with, or touched any of your O2 sensors?

I've never touched the O2 sensors except recently disconnecting them at the connectors to verify they throw the code.
I have a hand generic ODBII reader. I've been back to the smog station and they confirmed the same thing. Only O2 sensors not ready.
I did the drive test described in the manual and number of times. I drive the freeway for 20 mins a day and surface streets another 20 mins.

At 550 miles I finally got some codes. 0420 and a pending 0420. But, O2 sensors are still not ready.

Can the O2 sensor not working properly cause the 0420 ? Shouldn't there be a code for the O2 sensor ?

After I replaced a failing downstream 02 sensor (can't remember the code), I started getting the P0430 code. P0430/P0420 looks at the ratio of the switching time between the upstream and downstream sensors. The sensors tend to respond slower as they age (mine had 200k miles on them). When I replaced the bad downstream sensor with a new one, it was switching faster, and was then faster than 0.75x the rate my tired upstream sensor. I replaced the front sensor, and all is now good. They should be replace anyway if they have 100k+ miles on them, since a tired/slow front O2 sensor can decrease gas mileage and decrease the lifetime of the catalytic converter. Lucky for you, the front sensor on the right side (P0420) is easier to change.

Are you doing exactly the driving pattern in the FSM? It's an awfully crappy process and all, but I've never had it not work, and have had to do it a few times in different Nissans. It does have very specific MPH ranges, which absolutely suck (all the freeways here are 65-75, and the FSM calls for 53-60...you get a lot of a-holes staring you down as they fly by). My state (AZ) requires full readiness, but at no penalty for re-test.

If you're anywhere above 60 MPH, you're not within the driving pattern. The pattern (er, patterns...there are 4 for the entire test) is in the EC chapter under On Board Diagnostics System Description.

For the O2 readiness, you need two periods of 53-60 MPH. One is about 10 mins in that range (see Pattern 2). The second (Pattern 4) requires an acceleration to that range from stop, driving in range for at least 3 mins, then a deceleration and engine stop.

Many tests can be done in parts of course, but I do the entire pattern in one run...literally engine start, driving pattern, engine stop. I bring the printed FSM page, a co-pilot with a stop watch, and I drive out to an empty long stretch of highway at night (less traffic), then find some side/frontage road for the 0-30/35-0 tests, then back on the highway for the final pattern. I pull over on the side of the freeway when prescribed. Again, it's never failed me.

And just to be clear, and I think it was noted previously, but resetting the codes, clears the readiness. If you have codes and the monitors are ready, I wouldn't reset anything if you've got an emissions test coming up soon.

+1

Follow the FSM directions for resetting systems and they will all complete. The vehicle must be started with coolant temp at 95 or below and it must remain at 158 or higher while driving. If the cold wind cools the radiator too much, it wont complete. I used cardboard to block the front of the radiator in the cold weather so it would stay at 158.

So, an interesting follow-up observation on this...recently completed a very long road trip where I reset my ECU several times. On long stretches of 60-75 mph, I was able to make-ready all the sensors. In some cases, I reset the ECU while already at cruising speeds.

That said, there's some hope for a long trip working without having to do the driving pattern.

Colin (OP) doesn't seem to have returned here since Nov 7th.

Based on my experience, I think that he needs to replace the front O2 sensor, if he wants to get rid of the error code. FSM doesn't list the O2 sensor an a possible problem for that code, but it definitely is (and fixed the code for me).

Unless the code keeps the readiness from setting, I have no idea why he cannot get ready.

Bringing back an old thread but I am having a similar issue with my 02 Frontier and the o2s coming up as not ready. All other monitors are fine and I've done the drive cycle at least 4 times now with no luck. I have recently replaced both upstream o2s and the rear cats but haven't messed with the rear o2s because I read online those don't directly effect smog. But I'm now driving 6 months behind my tags because I cant get it to pass smog with my one monitor not ready. My question I guess is will replacing the rear(downstream) o2 sensors help me at all? at this point its either that or my computer.

Could be a grounding issue. I believe your model falls under that tsb. My 01 qx4 did not....but improving the grounds to my wiring harness fixed my o2 sensor issue