# Quick fix for codes (Emissions)



## airmn21 (Nov 30, 2005)

My emissions tests are nearly overdue. Unfortionatly I have a check engine light lit. I got the codes scanned and erased a few weeks ago, and the guy said that I had a missfire. I replaced the spark plugs and was good for a few days. Now the lights on again, so I went to auto zone and got scanned again, getting the codes PO138- O2 sensor and P0325 - Malfunction in the electrical circuit for knock sensor 1, and also got the missfire code again. Has anyone had problems with these codes? If I buy one of those code readers and erase it myself will I be abe to pass emissions, or can they actually see if your computer has been cleared? My plates are about to be revoked, and I realy dont have the money to go replacing things without knowing for sure. I plan on replacing the O2 sensor sometime this month but the knock sensor code is making me a little nervous. Any insight into this will be helpfull.


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## ibcleeby (Nov 22, 2005)

1) The knock sensor fault is a 'blind' code - meaning it will not trigger the check engine light by itself. The misfire and/or the O2 sensor codes are what is causing the light to appear. Also, don't be nervous about the knock sensor, it may cause your MPG to fall a little (retards spark timing some), but not replacing it should not damage your engine. 

2) You can read and erase the codes yourself easily using an ordinary screwdriver. Go here for the instructions:

http://vbxmaxima.8m.com/ecu.html

Using this procedure, you could reset the codes yourself right before your emissions inspection. Good Luck!


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## airmn21 (Nov 30, 2005)

*Thanks for the tip*

Thank you for the tip. I just went out and tried the method you described, I found the ECU, however mine is definitely different from the one in the picture. All of the screw holes are in the same position, except where the silver flathead screw should be there is a small plastic philips head screw, with what looks like an outer gear shaped screw around it labeled "idle speed adjust" I bought this car used, so I wonder if this is an aftermarket ECU? I couldn't find any reference to an "idle speed adjust" on the ECU in the owners manual or the Haynes repair manual. strange... I didn't have a screwdriver small enough to adjust it, so im going to go get one and try again tommorow.


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## ibcleeby (Nov 22, 2005)

I think I read somewhere that the later 4th gen Maximas have a Philips instead of flat-head screw, but the procedure is the same. Not sure about the 'idle speed' adjustment, though. I don't think my '95 has that.


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## ibcleeby (Nov 22, 2005)

.....also, be gentle with the plastic screw, it is more easily damaged than a metal one and you don't want to strip it - it should only turn 1 turn before stopping.


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## ibcleeby (Nov 22, 2005)

More help for ya....

Go here, post#25:

http://forums.maxima.org/showthread.php?t=104931


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## airmn21 (Nov 30, 2005)

*Light is off! for now...*

Thanks for all the replies, I finaly got the check engine light off. drove it around all day today with no problems, so I should be ok for emissions. Im glad I came to this site.


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## Matt93SE (Sep 17, 2003)

problem with resetting the codes is that it also resets the ready indicators. when you take the car in for emissions inspection, they check the readiness indicators.. If the car is shown as "not ready", they know you've reset the ECU recently and will tell you to come back after a few hundred miles.

generally it takes about 300 miles before the system shows all readiness tests to be good. before that, a 'not ready' test result will cause you to fail.


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## Redmax (Jun 23, 2005)

airmn21 said:


> Thank you for the tip. I just went out and tried the method you described, I found the ECU, however mine is definitely different from the one in the picture. All of the screw holes are in the same position, except where the silver flathead screw should be there is a small plastic philips head screw, with what looks like an outer gear shaped screw around it labeled "idle speed adjust" I bought this car used, so I wonder if this is an aftermarket ECU? I couldn't find any reference to an "idle speed adjust" on the ECU in the owners manual or the Haynes repair manual. strange... I didn't have a screwdriver small enough to adjust it, so im going to go get one and try again tommorow.



It's the factory ecu


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## airmn21 (Nov 30, 2005)

*Mission accomplished*

Thanks again for all the replies. I took the car in on friday, and it passed the emissions test. I wonder how long it takes for the computer to go through a cycle though, because while I did drive it around town after clearing the codes, there is no way I drove it 300 miles before getting tested. Anyways, mission accomplished, Thanks!


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## BORNGEARHEAD (Apr 30, 2002)

Why dont you just replace the O2 sensor?


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