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Discussion Starter #1 (Edited)
The sensor light on my 87 200sx with 175k miles came on a couple of months ago. Its my understanding that this is the oxygen sensor. Ive since replaced the oxygen sensor and attempted to reset the light by disconnecting the battery for several minutes. But the light remained on. Ive checked the single wire from the sensor to the control module and it shows good continuity, and also made sure the sensor is properly grounded, but the light will not clear. Also the diagnostics on the control module flash the “no errors” code. Lastly, other posts mention a sensor reset wire in the passenger side compartment, but i havent been able to find such a wire. Either way it seems to me that disconnecting the battery would clear any and all stored faults.

From posts in vArious forums Its my understanding that the sensor light will come on if theres a rich or lean feul mixture issue and not just a for a failinf O2 sensor. the car seems to be running rich (lots of carbon on the plugs). Aside from the carbon on the plugs it runs fine, though it could idle a bit better. Ive thoughly checked all of the ignition components-plugs, wires, cap, coils, distrib, timing- as well as the air cleaner, and tested all of the vacume lines and components w a vacume pump and found no problems., also 2 years ago I installed all new injectors, and last year I replaced the MAF unit. The compression is 145 psi +/- 5 for all cylinders. Recently ive tried leaning the feul mixture on the MAF but the light remains on. Lastly, Ive noticed that if I disconnect the pcv it idles much better (maybe because its getting more air?) but not really sure what that may indicate if anything

Anyone have any ideas what could be causing the light to stay on?
 

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Sup Mod keeping the peace
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There's a procedure where you can switch diagnostic modes in the ECU to clear out all fault codes; this should turn off the light on the dash. The procedure is located somewhere here on the forum but I can't locate it. Maybe someone here can chime in and point to it.

To test the PCV valve: Start the engine and while the engine is running at idle remove the ventilator hose from PCV valve. If the valve is working a hissing noise will be heard as air passes through the valve and a strong vacuum felt immediately when a finger is placed over the valve.
 

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NF Mod/Nissan Master Tech
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The "sensor" light is a maintenance reminder, not a warning light or check engine light. "Back in the day," (I say for the 4th time this week) Nissan recommended replacing the oxygen sensor every 30,000 mile service. It wasn't really needed at only 30,000 miles, but that was the thinking in the day. So, to be sure people did this...and be sure they would take their car back to the dealer...Nissan installed a "sensor" reminder which would turn on the light at 30,000 miles and need to be reset. They did this one of several ways. The earliest version would have the tech disconnect a wire at the specific interval. At the next interval, another wire would be disconnected. At 90,000 miles, the reminder module would be disconnected for good. You were on your own after that as far as Nissan was concerned! Later, they came up with a small module with a button on it that you would press to turn off the "sensor" light. Once you reset it, it would turn the "sensor" light back on at 30,000 miles from when you reset it, so it might not be exactly 60,000 or 90,000 miles. It could be 65,312 miles if it was reset at 35,312 miles. Get the picture? Some would have a small hole in the module where you would stick a small screwdriver or dental pick into and depress a button inside.

So, where is it on an '87 200SX? Try this link at Autozone's site and it might help you:

https://www.autozone.com/repairguides/Nissan-Stanza-200SX-240SX-1982-1992-Repair-Guide/EMISSION-CONTROLS/Maintenance-Reminder-Lights/_/P-0900c1528009989f
 
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