This one is 4 long 9 short or 0409. This code comes up undefined in the MIL code link on the Maxima FAQ page. Undefined means invalid code but I tried it 5 times before I reset it last night and it was the same every time. The light has yet to come back on since I reset it last night.
Does anyone know what this code could possibly mean?

 

Diagnostic Trouble Code 0409 indicates a problem with the front Oxygen Sensor on the right cylinder bank. The right bank is also called the rear bank. It is cylinders 1,3,5. The Engine Control Module determined that the response of the voltage signal from the sensor takes more time than it should. In simple terms, the Oxygen Sensor is still working but it is not doing its job well. Possible causes include ...
- Harness or connectors (the sensor circuit is open or shorted).
- Bad Oxygen Sensor sensing element
- Bad Oxygen Sensor heater
- Fuel pressure out of spec
- Fuel injector malfunction
- Intake air leaks
- Exhaust gas leaks
- Positive Crankcase Ventilation valve
- Mass Air Flow Sensor


The Oxygen Sensor sensing element may be tested with an electronic tester made for this purpose, or with an automotive oscilloscope. The Oxygen Sensor heater my be tested with an ohmmeter. This test is done with the engine off.

Follow the wires away from the Oxygen Sensor until you find the nearest electrical connector. Disconnect the connector. Viewed with the connector latch at the 12 o'clock position, there are three terminals. They are numbered 1-3, right to left. Be sure to measure the terminals in the connector half which is attached to the Oxygen Sensor, not the one which leads to the Engine Control Unit.

Measure the resistance between terminals 1 and 3.
The factory spec is 2.3-4.3 ohms at 77 degrees Fahrenheit.

Measure the resistance between terminals 1 and 2.
The reading should be infinity (no connection).

Measure the resistance between terminals 2 and 3.
The reading should be infinity (no connection).

 

Thanks Daniel, I have a digital multimeter and will run the tests that you have suggested. My car seems to be running fine and actually, i've gotten my best mileage in a long time over the last couple of weeks. I just had a rear oxygen sensor replaced last month, but I have a high mileage car: 98 w/105K since I commute ~120 miles round trip every day.

 

At 105K miles it is reasonable to expect the Oxygen Sensors to get tired and then fail altogether.

The signal from a healthy sensor varies from a low threshold (around 0.2 volts) to a high threshold (around 0.8 volts), and it sweeps back and forth between those extremes about 10 times per second. If a scope trace shows the Oxygen Sensor signal failing to reach either extreme, or oscillating between them at a frequency slower than 10 cycles per second, that is evidence of a "tired" sensor. If your digital voltmeter is one of the fancy models (Fluke 87, etc.) you may be able to use it in lieu of a scope to make this evaluation. Your DTC 0409 indicates the swing frequency is much less than 10hz. That's called a "tired" Oxygen Sensor.

I've read that a bad Oxygen Sensor can sometimes be rejuvenated by removing it, clamping it in a vise, and heating the sensing tip red hot with a propane torch. This is said to burn off a crust of deposits which interfere with its operation. I've never tried this torch trick myself, so cannot vouch for it's effectiveness. If you have a sensor which is already dead, you have little to lose.

For more information about Oxygen Sensors see:
http://www.volksparts.com/o2sensors.htm
http://members.aol.com/carleyware/library/o2sensor.htm

If you have the time and interest, you could exchange the two front Oxygen Sensors and reset the MIL. If DTC 0409 comes back the problem is not the sensor. If you get DTC 0413 that points to the sensor. DTC 0413 is the same as 0409, only it points to the left bank.

 

You are truly the man, I only wish I had the time to gain some of the in depth knowledge that you have but I will attempt to diagnose this problem myself since I can gain easy access to both front oxygen sensors.
I have a Wavetek 27XT Digital Multimeter, not top of the line but should be enough to perform these tests. I will be looking into it after work today. I don't visit the forum much on the weekends but I will try to post what I find out in case anyone is interested.

 

Ok guys I know DBM is no longer here but I have a question. I performed this test today on my car because I recently failed the emmisions on my inspection test. Where DBM said that I should get a 2.3 - 4.3 I read a 6.3 ... a decent amou8nt over. But also going by him and Chiltons' repair manual it says at 77 degrees. That is the part that throws me off. It is almost 100 degrees here today, would it be reading high because of the higher tempatures we are getting here now? Or is my O2 sensor just not working?

If any one knows it would be great. Thanks

SuDZ

 

bump

SuDZ