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O2 sensor light - 1980 US model

 
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Eric P  



Joined: 21 Jun 2017
Posts: 164
Location: NY, USA

PostPosted: Thu Jun 14, 2018 2:56 am    Post subject: O2 sensor light - 1980 US model Reply with quote

As of a few weeks ago, I've had the "OXS" light on my dash come on. It was my understanding that there's a counter on the speedometer cable that turns the light on every 30k miles. I've also read that I can reset it by pushing a button under the dash. I don't doubt that it's probably time to replace the O2 sensor as I have no records of it being done and I'm at 81k miles. I assume it must have been replaced at least once in the past but who knows.

Anyway, my confusion is with the fact that the light on the dash comes on when I start the car but goes off as soon as I rev the engine for the first time after starting? It goes off whether I'm moving or not. Is it normal operation for this light to go off on its own until the car is started the next time? I thought once the light came on, it stayed on until the counter box was reset? Do I have another gremlin living in my car? I thought I finally had them eradicated but maybe not

On the same note, does someone have a picture of the reset button so I know what I'm looking for after I replace the sensor? I have the Haynes manual, but apparently the page I need is missing. That's what I get for buying used books I guess.

I tried searching, but came up empty handed. I'm assuming this is because ROW and early US models didn't have an O2 sensor.
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1980 924 NA, US model
1987 924S, US model
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1498
Location: Not Detriot - NMI

PostPosted: Thu Jun 14, 2018 4:54 am    Post subject: Reply with quote

I think the reset is on the box in the middle of the speedo cable under the hood..
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Eric P  



Joined: 21 Jun 2017
Posts: 164
Location: NY, USA

PostPosted: Fri Jun 15, 2018 12:46 am    Post subject: Reply with quote

I was able to bum a wiring diagram off a friend for the O2 circuit. It appears that there's an "RPM relay" somewhere which I assume is the counter. There's also an O2 control box. The Haynes manual doesn't say how to test either of these boxes and simply states that the control box isn't repairable if broken.

The control box is under the dash and the counter (with reset button) is on the left front wheel well and accessed from under the car. Apparently yopu need to take the belly pan off the car to see it.

In other news, my alternator died again. I had just replaced it last spring so hopefully it's under warranty. I'm wondering if the O2 light coming on was due to low voltage at the O2 "rpm relay" that turns the light on. My battery light only comes on when I start the car whether the alternator is working or not.

So the long and short of it is that I'm replacing my alternator tonight. I'll test it to see if the light comes on still for my own curiosity then and I'll be replacing the O2 sensor either way.
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1980 924 NA, US model
1987 924S, US model
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Eric P  



Joined: 21 Jun 2017
Posts: 164
Location: NY, USA

PostPosted: Sat Jun 16, 2018 2:35 am    Post subject: Reply with quote

Here is a followup for anyone reading this thread in the future:

A bad alternator can make the OXS light come on. My alternator was only putting out about 12.5 volts and only after revving the car a bit, hence why the light goes off after revving the car. A new alternator and the OXS light is off. I ordered a new O2 sensor anyway and will be replacing it due to unknown history. I'm also looking at a new catalytic converter. After driving my '87, it feels like it has more than 40 hp on my '80 and freeing up the exhaust flow a bit can't hurt.

As far as the alternator, I'm still confused why my alternator dash light didn't come on when the alternator went. The light works at startup so the bulb isn't blown. Anyway, if your OXS light is going on and off without resetting the counter, check your alternator output. Your alternator could be on its way out.
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1980 924 NA, US model
1987 924S, US model
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