89 240sx engine light

[nolefturns]

I replaced the o2 sensor under the hood below the 4th, farthest from the distributor cap/rotor, with a BOSCH one and engine light is still on during random driving. However it stays on less often than before with the previous o2 sensor I replaced. It use to stay on for perhaps 10+ minutes at random times and days of driving. Now with the new o2 sensor, it would stay on for at most a couple of minutes at a time but still random times and days of driving. I heard there might be a rear o2 sensor that I read in one of the threads but I couldn't find it anywhere underneath the car. What else can I look for? What can I do? I want to get rid of the engine light if I can.

Any thoughts, advise, suggest, comments are welcome, thanks.

[TrueSlide]

The 89 has a engine light?

[nolefturns]

Check engine light.