DCmax

iTrader: (2)

I was running errands with my father and brother today and after shopping I went out to my car, started it, and the ML light went on.

The codes were 0303 - Front Left Heated O2 Sensor
and 0304 - Knock Sensor

What does this mean?

My car is a 96 GXE Auto and I do have a JWT Intake but ive had it for 4 months without a problem and 2 weeks ago I took my car in for regular service.

Any help is much appreciated.

Daniel B. Martin

Diagnostic Trouble Code 0303 indicates a problem with the front Oxygen Sensor on the left cylinder bank. The left bank is also called the front bank. It is cylinders 2,4,6. A normal signal sweeps back and forth between 0.2 volts and 0.8 volts. This malfunction was detected when the Engine Control Module received a signal from the sensor which was a constant value of approximately 0.3 volts.

Possible causes include ...
- Harness or connectors (the sensor circuit is open or shorted).
- Defective Oxygen Sensor

Daniel B. Martin

Diagnostic Trouble Code 0304 points to a problem with the Knock Sensor. The KS is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is senses as vibrational pressure. This pressure is converted into a voltage signal and sent to the Engine Control Module (The computer).

This malfunction is detected when an excessively high or low voltage from the KS is entered to the ECM. Possible causes include...
- the harness or connector (The KS circuit is open or shorted).
- the KS

The KS may be checked with an ohmmeter.

1) Raise the hood. View the engine from the driver's fender. Look into
the deep valley between the cylinder banks and below the intake manifold.
Identify the KS as a black item fastened to the block by a single vertical
bolt. A wire harness wrapped in black leads toward you, out of the valley.
That is the KS sub-harness.

2) Follow the KS sub-harness to it's nearest connector. This is connector F121.
It is located near the upper right-hand corner of the valve cover of the forward cylinder bank, as viewed from the front of the car.

3) Disconnect F121. You have to do a "press the latch and wiggle and
pull" to disconnect it. F121 has only two pins; if you see more than two
pins, you have the wrong connector. Use a digital ohmmeter capable of
measuring more than 10 Megohms. You want to measure the pins of F121, not
the sockets of the matching connector. Measure the resistance between a
good ground (such as the battery negative terminal) and pin #2 of connector
F121. On my car this is the highest of the two pins, the one closest to
the front of the car. The factory spec is 500 - 620 Kohms.

The manual says you have to remove the intake manifold to replace the KS. However, I think that a person with good dexterity and a 10mm ratcheting box wrench could replace the KS without disturbing the manifold.

Important note: the dealer can do a more thorough test with his CONSULT electronic tester. The resistance test described here is a useful but limited test. A Knock Sensor which fails this test is definitely bad. However, a KS which passes this test is not guaranteed to be good.

DCmax

iTrader: (2)

Daniel, thank you for your response.

Is it possible the malfunction was a freak incident? After I checked my ECU for the diagnostic codes, the ML light went off and hasnt come back on since.

I checked to make sure my 02 sensor was secure in my air filter, but you said it was possible that it could be defective. If this is the case, how would you going about checking if this was the case. Should I continue driving regularly for a week or so and see if the ML light goes on again?

My car is still under warranty but Im sure that the dealer will not cover this area since my 02 sensor ofcourse isnt in its stock location.

thanks

Daniel B. Martin

Possible but not likely.

Your '96 Maxima has three Oxygen Sensors. The two front sensors are located in the Y-pipe and the rear sensor is located just downstream of the Three-Way Catalytic Converter. You should not have an Oxygen Sensor in your air filter.

There is some confusion here. If you really have an Oxygen Sensor in your air filter it cannot possibly work right. Perhaps you are referring to a different sensor.

DCmax

iTrader: (2)

I think there maybe some confusion. I was referring to the sensor that was mounted to my stock airbox but I moved to my airfilter when I installed my aftermarket intake. Im sure Im just confused.

Is there any relation between the sensor located in my air filter to the sensors you are referring to?

The reason I ask, is when I go into the dealer, I want to make sure the problem isnt due to my intake, thus voiding whatever coverage from Nissan I would get.

Daniel B. Martin

Perhaps you are referring to the Intake Air Temperature Sensor. There is no direct relationship between the IATS and the Oxygen Sensors. They all send signals to the Engine Control Module (the computer) but are not otherwise connected.

The issue of warranty coverage is a gray area. Some dealers are very tolerant of mods. Others will seize on a mod and try to blame it for all sorts of unrelated mechanical maladies.

DCmax

iTrader: (2)

Thanks for all of your help Daniel, Im going to get it checked out.