my '95 Maxima gets just 14 mpg in city driving. it used to get 18 mpg in city. took the car to dealer for diagnosis. the hose from valve cover to air intake just after the MAF has been disconnected because the nipple broke off at the air intake housing. first I was told I needed to replace the MAF sensor. after installing an aftermarket MAF sensor the mileage did not change, went to dealer again and was told one ignition coil was the wrong one. so I replaced that coil yet that did not change the mpg. the ignition coils are all fine now. took the car to the dealer a third time and now am told a code P0150 shows that an oxygen sensor is showing something extraordinary and the catalytic converter is not functioning correctly. the technician thinks misfires have damaged the catalytic converter (and I did have a blown head gasket last year but the 14 mpg has been since before the head gasket was repaired. Could a bad catalytic converter be causing my car to be getting just 14 mpg?

 

DONT EVER USE aftermarket maf sensors. They will never work and throw codes that were never supposed to come up. Put back the original maf sensor in the car and return the aftermarket one. Your mass air flow sensor is not bad. Also P0150 is bad oxygen sensor which is the cause of your bad gas mpg. Your dealer is really stupid and not smart at all telling you to replace the maf and catalytic converter for no reason at all. P0150 - O2 Sensor Circuit Malfunction Bank 2 Sensor 1 Replace the sensor and your good to go.



Read more: http://www.engine-codes.com/p0150.html#ixzz3s5dwHlGR

 

In my experience with my 97 auto, Changing solely the cat which I was told was faulty for whatever reason, gave me no difference in gas mileage. Although I could feel a very noticeable powerloss upon getting a replacement.

 

ehhh possibly not enough to notice a difference or anything....

 

Thank you for your response 'Maxima 97 SE'. the site you referenced -- engine-codes.com does not show a 95 Maxima as a relevant vehicle. my 95 has an OBD one diagnostic. the technician's notes did indicate O2 sensor was basis for code P0150 and he wrote that the catalytic converter was causing the issue. (the code which indicated my original MAF sensor did not show up after I installed the after market MAF sensor. the new MAF sensor did not improve the poor mileage I was getting so I agree my original MAF sensor was not bad.) Now I wonder if the technician is correct about the catalytic converter causing the O2 sensor to generate the P0150. The service writer told me that misfires had caused the catalytic converter to go bad and according to the technician, the car would not pass a smog check because of the catalytic converter.

Also, I have an air leak at the air intake duct just after the MAF Sensor where the hose from the valve cover to air intake meets air intake. and this air leak is causing the engine to run lean. I don't think this was the cause of the poor mileage since I had that leak temporarily sealed for a time and the mileage was no better during that time. when the mpg went down to 14 from 18 it was sudden. I will use a metal tube to seal that leak (where the hose connects the top of a valve cover to the intake duct). I had two oxygen sensors replaced but I don't know how many O2 sensors there are on the car (maybe 4?). This is frustrating me that the dealer did not pinpoint the problem. Also, why didn't the technician mention the air leak which is next to the MAF sensor when he recommended replacement of the MAF?

 

Actually all nissan maxima 95-99 are obd2 and not one. Nissan implemented the obd2 system way before it was required in the 95 maxima. So what ever he said about the catalytic converter is wrong. He thinks its causing the code but its not becuase the sensor after having so many miles goes bad and you have to replace them every 100,00 miles or more when a code pops up. Trust me, you should forget about the cat and focus on getting a new o2 sensor. When my fuel injector O-rings went bad on my 97 maxima, the dealers said it was a bad catalytic converter because it was throwing out raw fuel out the tailpipe. I said no way catalytic converter is bad and i had 280,000 miles at the time on my car. I fixed my O-rings and now at 322,000 miles my cat is still running like its new. If you really want to spend 500-1000 dollars on a new catalytic converter instead of buying a new 02 sensor for about 50.00 dollars, go ahead. Looks the dealer has convinced you that its a bad catalytic converter. Oh by the way a bad catalytic or one that is not functioning right will throw the code p0420, P0420 Catalyst System Efficiency Below Threshold and not an o2 sensor code which you have is P0150. Also there are 4 sensors on the 95 maxima. Just look at the picture. The one you need is Bank 2 Sensor 1 if you look at the picture it will show you the exact location. Also an inatke air leak needs to be fixed right, so you need to replace the intake air duct with a new one. It also might take care of the o2 sensor code because the computer know theres an air leak somewhere and it affects o2 reading which might be causing the code to pop up. Try replacing intake air duct first and then do the rest if you have to. But forget about the catalytic converter for now as you dont have catalytic converter code like P0420, which is only cat related.

 

when describing the P0150 code, the factory service manual says left bank. is left bank the radiator side (not firewall side) of engine? I see a diagram (at http://www.engine-codes.com/p0150_nissan.html) which labels B1 and B2 opposite of the diagram above.
further-- I see this (from http://troubleshootmyvehicle.com/nis...stic-tests-1):

NOTE: Bank 2 is the bank that houses cylinders 2, 4, and 6.
•Bank 2 Sensor 1 is commonly referred to as: ◦Left front oxygen sensor.
◦Upstream left oxygen sensor.
◦Bank 2 Sensor 1.
◦O2S21.

this image shows bank 2 on the radiator side.

 

there two upstream o2 sensors. One is in the front and the one that you need to replace is above the oil pan. Like the picture says Bank 2 upstream sensor 1

 

sorry, but I want to confirm bank 2, sensor 1 on the radiator side near the oil dip stick. regardless, the O2 sensor is new and the car is running lean. If so, what is the cause of the lean mix? Possibly the lean mix is because I have the air leak in the air intake tube right after the MAF sensor. My point being could the P0150 just indicate too lean or does the P0150 definitely mean bad sensor?

Usually the cause of P0150 is a bad oxygen sensor, however this isn't always the case. If your o2 sensors haven't been replaced and they are old, it's a good bet that the sensor is the problem. But, It could be caused by any of the following:
• Water or corrosion in the connector
•Loose terminals in the connector
•Wiring burnt on exhaust components
• Open or short in the wiring due to rubbing on engine components
• Holes in exhaust allowing unmetered oxygen into exhaust system
• Unmetered vacuum leak at the engine
• Bad o2 sensor
• Bad PCM

 

No there are 2 front sensors. Its not the one near the radiator and oil dipstick pan. Its behind the engine. There a wire thats on top of the intake manifold that goes all the way down the sensor.Also put back the original mass air flow sensor and that will fix the lean mixture. Every single person on this forum knows that aftermarket mafs have never worked and never will. Then fix the intake air leak and then erase the code from the car and drive it and see if it comes back. Do those things first and go from there and if you dont fix those things you might be just waisting money and time on things that are not bad.

 

the sensor is on the side of the engine that faces the fire wall. Fixing the sensor may help with the problem. Fixing air leaks might help. Yes, oem maf only.

Some members have had a cap on a fuel injector crack. this allows lots of gasoline to leak past the injector. the problem injector might not throw a code, but emissions will skyrocket while gas mileage craters. Look for posts on the forum about cracked pintile caps.

 

on page EC-142 in the factory service manual there is an illustration of the radiator side of the engine (with the oil filler cap) and the front heated oxygen sensor harness connector (left bank and DTC P0150) clearly is marked.

 

But that is not the one you want to replace. It is on the engine by the firewall.

 

You need to make sure you're replacing the right sensor. Get under your car and look around.

These dealers will tell us whatever will line their pockets with our dollars. My advice is, buy a check engine reader and Google the code numbers. That alone will give you far more information than the idiots at the dealership, not to mention save you money and hassle replacing OK parts because of misinformation.

 

+1 with what Maxima 297 said. The scanner costs less than 50 bucks.