my 1997 infiniti i30(same as Nissan maxima) with 157k miles

[eagle0913]

well my check engine light went on like 2 months ago, went to autozone got the codes, P0325, generic knock sensor, and P0136, generic o2 sensor, so… of recent i have put in highest grade fuel(owners manual says so) got about 22-23, about average for the car, then the past few times ive gotten 20 and 19, so that would be the o2 sensor im assuming? i not that educated as far as the actual components of a car, i just know useless specs haha. Also we have reset the codes twice, just to see if they would come back on or not and they have, so what should or shouldnt be replaced? could it be a faulty computer because im

Topic

[dreamer2355]

Welcome to the forums!

You would need to follow service information and scan tool data to help diagnose those particular issues.

For the P0136, check the wiring for any shorts to ground as well as a good visual inspection of the wiring. It may be a slow responding sensor or you may have an a hole in the exhaust near the o2 sensor.

Same principle applies to the P0325. However, you may be able to ohm out that sensor if you know what factory values are.

[EricTheCarGuy]

I’d like to add a couple of things if I may. For some reason mice like to hang out under the intake and I’ve seen them chew the wires to the knock sensor so it may not be the sensor but rather the wiring and as pointed out that area gets a lot of heat which can degrade the wires and make them brittle which can cause them to break as well. Also if the computer sees or senses a knock sensor signal it retards the timing which can cause a reduction in fuel mileage.

You could always observe the O2 readings on a scan tool that shows live data (sometimes they have these at the auto parts store), you want to see the sensor switching back and forth fairly rapidly over the .5v mark if it’s working properly.

[skim3544]

P0325 is a common problem for these VQ engines because this thing is buried between the rear V section of the block where it gets exposed to a lot of heat. it is also pain in the butt to take these out and install a new one. You can barely see the sensor, and very little room to turn the tool. On top of that, lot of sharp edges sticking out from the intake mounting point so I would not advise you to stick your hand between the V and take it out – you would end up with many deep cuts Use U-joint and extension to get to the bolt. I would also replace the wiring connection. It is just small clip on wire.

I agree with dreamer on O2 sensor – make a visual check first. You don’t need to throw money at it unless you have to.
VQ ECU does not use the values from the rear O2 sensors for engine operation. It will still throw code, but only the front 2 O2 sensors are used for engine operation and rear ones are used for for status and error reporting only. So your assumption is incorrect.

[eagle0913]

Thank you guys so much! Very insightful on the rat thing because in fact the car used to sit next to the garage, it was my father’s car at the time, and he had to put rat poison near it because they were building a nest in the engine bay, but the check engine light didnt come on until recently. It hasnt sat in that spot in almost a year. The only thing I wish is if yall could dumb it down, I wish I fully understood all of what you are saying haha, but i still greatly appreciate the help, put a big smile on my face just to get feedback! Love the show Eric! I support the show!

[skim3544]

You are likely looking at knock sensor and wire replacement:
http://www.youtube.com/watch?v=R2ntaxi7bXk

There are several ebay vendors selling aftermarket knock sensors cheap – OE sensor runs around $50 and your car needs just 1

http://www.ebay.com/itm/KS79-Knock-Sens … 3f0df83bbe

The sensor wire also gets brittle and you should replace while doing this job – wire costs around $15

For O2 sensors, to properly diagnose it, you would need a lap scope ($1000+ ). But if you just check the wires and everything appears to be Ok, you should just replace it. Another basic test you can do is to use ohm meter and and volt meter measure the sensor at room temperature and while it is hot (which can be dangerous) But when in doubt I would just replace the sensor – I picked up Bosch sensor for this car for $65 just a month ago due to failed emission test. Installing is pain and is usually the rear O2 sensor (located right after the catalytic converter) goes out and the wire connection runs from the sensor to the cabin under the driver’s seat.

For the most sensors, it takes O2 sensor tool and long extension – takes about 10 minutes to replace the sensor. For this car, you do not have enough space so you need to remove rear exhaust hangers and support the system with the jack and lower it little bit to create more space. Took me 1 – 2 hour to replace this.

The both of these are very common problem for these VQ engines. For some reason the rear O2 sensor goes out before anything else.

[dreamer2355]

Using a scan tool that can show live PID and graph data is also another alternative then using a lab scope. O2 sensor circuits are very easy to diagnose.
Also using a DVOM, you can also check the integrity of the heater circuit as well as carrying out voltage drop tests also.

If the OP does decide to just ‘replace’ the knock sensor, i would recommend using an OE replacement as well as making sure the sensor it torqued down to specifications due to to loose or too tight knock sensor bolts can cause issues.

This video here shows you how to property diagnose a knock sensor with the right equipment –

http://www.youtube.com/watch?v=vqj2YWbe … THvj3Rd2vX

The other method is to use a timing light and tap around the location of the knock sensor to see if the timing changes. However, with this been a newer vehicle, that method may not be viable.

[EricTheCarGuy]

Thanks for supporting the show! By the sound of things it might be worth getting in there to get a look at that knock sensor and it’s wiring, I suspect you’ll find a rats nest under there and some chewed wires.

[Author]

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