# P0300 & P0141 Codes



## chadzeilenga (Apr 15, 2009)

I just finished replacing the 1.6L in my 1999 Sentra. Now I have a CEL with a P0300 (Random cyl missfire) & P0141 code (O2 fault???). Is anyone familiar with these? I did a search and nothing came up. The car seems to be randomly misfiring. I pulled the plugs one at a time and #3 had some water in the bottom of it. Probably from the wash they gave it before they sold it. Would these cause both of my issues?


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## jdg (Aug 27, 2009)

Loose wiring on the distributor side of things...Vacuum leak...Timing not set right...

I would think that the P0141 is being caused by the P0300, so I'd ignore that for the moment, even to the point of disconnecting your O2 sensors entirely, forcing the ECU into open loop so you can troubleshoot the misfire without the computer trying to compensate for it.


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## chadzeilenga (Apr 15, 2009)

*Think I figured it out...*

I was trouble shooting the misfire on the car tonight. 

I thought I had it figured out with the water in the plug well, but that wasn't it. I first swapped the cap, rotor & wires from a 25k mi engine I had in the garage and no improvement. 

Next I decided to look at the plugs and the porcelain on #3 was cracked allowing the plug to arc out. I swapped it and then resent my CEL. Drove it around a bit tonight and no light so I think the P0141 was being caused by the P0300. I'll drive it more tomorrow to make sure.


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## chadzeilenga (Apr 15, 2009)

*It's back...*

I thought I had the random misfire figured out last night with the cracked plug, but it's definitely back. What could cause a random misfire? It happens once the car has warmed up and is either while idling or driving around although it doesn't happen all of the time, comes & goes.


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## IanH (Feb 11, 2003)

Since you have a spare distributor I would recommend swapping the whole thing out.


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## chadzeilenga (Apr 15, 2009)

I'll have to do that tonight. There also seems to be a strange random clicking sound coming from the distributor area too.

I've got 2 spare GA16DE engines in my garage right now so luckily I have access to spare parts.


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## chadzeilenga (Apr 15, 2009)

*Did the trick*

Thanks for the idea Ian. The junkyard engine I got didn't have a distributor so I used the one off the engine with 135k mi on it, but I have another blown engine that only has 25k mi on it and that distributor worked great. No problems. Now I just have to reset the CEL or let it do it on it's own.


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## jdg (Aug 27, 2009)

chadzeilenga said:


> Thanks for the idea Ian. The junkyard engine I got didn't have a distributor so I used the one off the engine with 135k mi on it, but I have another blown engine that only has 25k mi on it and that distributor worked great. No problems. Now I just have to reset the CEL or let it do it on it's own.


That's cool...practically free fix.
'Let it do it on it's own' - may take something like 50 driving cycles to do that. Time for a small chunk of black electrical tape! Either that or just run down to the local Autozone or whatever and have them pull/reset the code.


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## chadzeilenga (Apr 15, 2009)

*Reset ECM manually*

Yea, I might just reset the CEL manually thru the ECM. I still can't believe that they put the screw facing the firewall!!! Maxima's are nice and easy to get to right by the gas pedal.


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## IanH (Feb 11, 2003)

it took over a week of normal driving for mine to re-set, or just dis-connect the battery for a few hours.


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## chadzeilenga (Apr 15, 2009)

*P0141 Code is back*

Drove the car today for a while around town running errands. The CEL came back on. Stopped by Autozone and they read it to be the rear O2 sensor. Do these O2 sensors usually go out or is there something else that could be triggering it?


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## jdg (Aug 27, 2009)

chadzeilenga said:


> Drove the car today for a while around town running errands. The CEL came back on. Stopped by Autozone and they read it to be the rear O2 sensor. Do these O2 sensors usually go out or is there something else that could be triggering it?


Need to know exactly which code tripped. Could be bad O2 sensor, could be bad cat, could be an exhaust leak, could be this, could be that. O2 sensors do go bad, not usually, but could happen.


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## chadzeilenga (Apr 15, 2009)

Hello,
I pulled the code today from the ECM and it was a P0902 code which in the manual says is the 2nd O2 sensor. 

I also notice that the car seems to run hot as the cooling fans are on often. I don't know if that is an issue with timing or not though, have to check.

Other than that it runs really well.


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## jdg (Aug 27, 2009)

chadzeilenga said:


> Hello,
> I pulled the code today from the ECM and it was a P0902 code which in the manual says is the 2nd O2 sensor.
> 
> I also notice that the car seems to run hot as the cooling fans are on often. I don't know if that is an issue with timing or not though, have to check.
> ...


Since you had the other problems, I'm thinking maybe the engine might've polluted the cat and the 2nd O2 sensor a bit. Especially with a random misfire. Raw gas going out of the engine, plugging up the cat.

If it was me, I'd let the light come on, let it stay on, run some good quality gas thru it (not necessarily high octane gas, 'cause that doesn't automatically mean good quality, I mean don't run gas from the local Walmart or whatever, go to a reputable gas station for awhile, even if it costs more). Then after a few hundred miles or so, clear the light and see what happens.

Entirely possible you wrecked the cat by running raw fuel thru it (which is what usually happens by default when you get a good misfire). Doubt if you wrecked the O2 sensor. Sure...couldn't be the cheap easy part, has to be the hard, expensive part...

I'm almost positive the code wouldn't have anything to do with the engine running warm, although timing could easily have an impact on that. Put the timing back to stock and see what happens.


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## chadzeilenga (Apr 15, 2009)

Hmmm. I narrowed the random misfire down the the cracked plug and the bad distributor. I didn't drive the car much when I was getting the misfire, maybe 10-15 miles total.

Would that be enough raw fuel to ruin the cat? How would I know if the cat was bad? The car seems to run ok and is smooth now.


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## jdg (Aug 27, 2009)

From what I've read, it doesn't take much to wreck/poison a cat. And I'm sure it does run smooth and just fine, and most likely will run just fine without a cat and a downstream O2 sensor. It's just that those clowns at the EPA and CARB years ago decided that those sensors have to be in everything. Keep driving it, let it ride for awhile and see what happens after a couple of weeks.


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