91 240sx KA24DE ECU code 34 - Help?

[basic_mod]

Hello all. Yesterday, I decided to check my ECU for codes, as I have been getting poor gas mileage . Checked the codes and it spit out a code 33 and code 34. The code 33 is the o2 sensor, and the code 34 is the knock sensor.

After running the o2 sensor test (as described here on NICO) the light goes on and stays on for about 10 seconds, then turns off for about 10 seconds, then turns back on..etc - indicating a bad o2 sensor. Anyway, i've got a replacement o2 sensor that I will be putting in tomorrow to fix that issue.

My question is about the code 34. Does this mean that the engine has a knock (I haven't noticed any knocking or pinging) or just that the sensor is bad? I reset the ecu code, then took a drive to the parts store to pick up the o2 sensor. After getting home, it only spit out the code 34.

Also, while a long shot, will the new o2 sensor help with the code 34 or is it the knock sensor for sure?

I think my mileage problems started back in Jan i think when I overheated the car due to the water pump going out. After replacing the waterpump and thermostat, it cools just fine. There's no oil being burnt, no oil in the coolant and no coolant in the oil, nor is there any bubbles in the coolant, so I don't think the head was at all damaged, but it does run rich. That being said, could the knock sensor have gotten damaged from the overheat and given the fact that it is almost 20 years old? And, could the damaged knock sensor have caused the decreased milage (retarded timing and more fuel since the ecu doesn't know if the motor is knocking or not) and if so, could this overly rich condition have caused the o2 sensor to go out? If so, I don't want to replace the o2 sensor until I can get the knock sensor fixed to avoid ruining another o2 sensor

Thanks.
Modified by basic_mod at 11:52 AM 6/3/2009

[PapaSmurf2k3]

Its more likely that the O2 sensor caused a lean condition, which caused the engine to knock, so there is a possibility that both codes will go away once you replace the O2 sensor, an reset the ECU.

[d-wade]

Any updates on your conditions? I'm having the same issue. I just replaced my Knock sensor and still have both codes. LMK!

[basic_mod]

Honestly, i have yet to replace the knock sensor. I have it, just haven't found the time to do so. I have replaced the o2 sensor, and that fixed the code 33. Right now I have the code 34 fixed by jumping the white wire in the knock sensor plug (the one that plugs into the subharness) to ground through a 1 mega-ohm resistor. THe code went away after that, but I still need to get the sensor replaced. Some day when it's not 100 degrees and raining, maybe I can get around to that.