Your '85 T should have O2 sensor pre-heater... - Saab 900 Bulletin Board - Saabnet.com
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Your '85 T should have O2 sensor pre-heater...
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Posted by Micah in NC [Email] (more from Micah in NC) on Mon, 18 Nov 2002 16:53:52 Share Post by Email
In Reply to: O2 sensor warm-up, JJ, Mon, 18 Nov 2002 16:32:11
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Chris,
As you may know, your Turbo is advanced compared to, say, a non-turbo '85. One of those advances is the type of O2 sensor used; yours is electrically heated with 3 wires: 1 = signal voltage wire (black), 2 = preheater voltage (white).

The "regular" '85s (and older 900 cars) didn't have this type of sensor, they just had a single-(black)wire sensor which didn't preheat; this type relied solely on exhaust temps to heat sensor to operating range. Your 3-wire type is supposed to get sensor operating faster and engine into "closed-loop" fuel injection program faster = more efficiency.

That said, I'd unplug and check the two white wires going to the O2 sensor (look for 12V) w/ignition on and also check the sensor's preheater resistance (look for 2-4 ohms, if I remember correctly).

If no volts to O2 preheater, then look at the fuse (in-line fuse on your '85T, I think). If zero ohms, or infinite ohms, suspect O2's heater is faulty.

Also, get a digital VOM (volt-ohm meter) and check the O2 sensor's output voltage. If its output--at black wire--doesn't swing from about 0.2 to 0.9 volts, or if no volts obtained once car is warm, then replace the sensor.

If you do replace it, you can apparently save some $$$ and use a Ford Mustang 5.0L engine's O2 sensor, if you care to splice some wires. See the FAQ (Frequently Asked Questions) list and O2 Sensor page off the home page of this site for more info.

Micah in NC
'84 900S, 224K mi. (single-wire O2)
'90 900, 69K mi. (3-wire O2 sensor)

posted by 67.35.16...

Click here for my (fledgling) page on O2 sensor tests.

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