tonymich

Some time ago I made a post about my Check Engine light coming on in my 95 Maxima SE. The codes were:

0304 = Knock Sensor or circuit

0707 = Oxygen Sensor, right bank

This has happened 3 times (reset each time) with the same codes. That makes me suspicious that something is not quite as it seems. .

I have been to my mechanic who says replacing these sensors will be @ $800, and that the light may still come back on again!!!.

These are my questions--any help is greatly appreciated.

1. Are these two sensors somehow connected or dependent on one another? No one I've talked to thinks so, but 0304 and 0707 always come on together.

2. if they are not dependent on one another, why would they come on together 3 times?

3. I have noticed no change in the performance of the car. Is damage done by driving the car while I'm trying to figure this out?

4. What are the chances that this is an electrical issue, and that there is no "fix"?

5. I get blank looks when I ask repair people to check the sensors before replacing them. I read a post by D. Martin that describes how to check the knock sensor. Why don't mechanics know about this? Can they be checked, and if so, at what expense?

6. Am I better off with a Nissan mechanic?

Thank you for any help you can provide.

Daniel B. Martin

You have asked some good questions. I'll try to answer, but please understand that I'm venturing outside of knowledge and into the realm of speculation.

There is no direct connection. There could be a cause-and-effect indirect connection.


Let's suppose there is a defect with the Oxygen Sensor. The Engine Control Module could be mislead into thinking the fuel mixture is too rich. The ECM adjusts the fuel mixture to become leaner. The leaner mixture provokes a brief period of severe engine knock (pinging). The pinging causes a marginal Knock Sensor to go "over the edge" and exhibit an out-of-range resistance value. The ECM decides the Knock Sensor is "bonkers" and does these things
(1) Decides to ignore signals from the KS.
(2) Set Diagnostic Trouble Code 0304.
(3) Turn on the Malfunction Indicator Light (a/k/a Check Engine Light, Service Engine Soon light).

Meanwhile, the defective Oxygen Sensor is still sending inaccurate data to the ECM, and try as it might, the ECM cannot make the fuel mixture lean enough to satisfy the Oxygen Sensor. After a few more seconds of this, the ECM does these things
(1) Decides to ignore signals from the OS.
(2) Sets Diagnostic Trouble Code 0707.
(3) Turn on the MIL, but you don't see this action as a seperate event because it was already on.


The performance of the car is changed, but in such a minor way that it escapes the human senses. It might not escape the "sniffer test" at the next State Inspection. One of your two forward Oxygen Sensors is "out of action", causing more emissions, placing a larger burden on the Catalytic Converter. This will cause the "cat" to run hot and die sooner.

There is a "fix", it just hasn't been found yet.


A blank look may be an indication of ignorance. The factory service manual explains how sensors are tested. The aftermarket repair manuals (Chilton, Haynes) give less detailed instructions for testing sensors, but they do address the subject.

Testing the Oxygen Sensor:
Chilton page 4-13.
Haynes, page 6-14.

Testing the Knock Sensor:
Chilton, page 4-22.
Haynes, page 6-16.

Note that the dealer, using his sophisticated CONSULT electronic test device, can do a more thorough test than those provided by Chilton or Haynes.

IMHO the dealer should do a thorough CONSULT diagnostic procedure, including tests of the two suspect sensors, for the charge of one hour of labor.

You are better off with a better mechanic. That man might be employed by a Nissan dealer. He might be a competent technician employed by an independent repair shop. Ask your neighbors, friends, coworkers for recommendations. You might find an experienced Nissan dealer technician who has opened his own repair shop. That's a good man to know!

Good luck!