1994 850 Turbo 145k miles

The check engine would come on randomly and show code 1-2-3 (ECT sensor) for the last few months. It might be a few weeks before it came back or just a day or two, so I decided to swap out the thermostat and ECT sensor last weekend. Now about every time the car is driven the check engine light will come on after the car is running about 5 minutes (during warmup). Each time it is code 1-2-3, and will otherwise run and drive fine. If I shut off the car and clear the code, then restart (engine already warm) the check engine light will not reappear until the car is shutdown and cooled down for the night. The temp guage is exactly at the 3'o clock position when warm.

Could it be any leftover air in the cooling system (I drained and replaced it during install)? Any other ideas? I expected the new thermostat and ECT sensor would do the trick, and the car has been driven about 200 miles since replacement, so I figured any air would have bubbled out to the expansion tank by now.

Thanks,

Zack
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Zack Silver 83' 242Ti (230k)

Use your multimeter and check the 0hms of the ECT. Will Resper wrote:

Temperature - deg F ( deg C) Ohms
850 & 960
32 (0) ....................... 7300
68 (20) ...................... 2800
176 (80) ..................... 300
212 (100) .................... 150

These days it should be around 68F in the garage with the engine cold, so around 2800 would be good.

Klaus

I doubt that it is a matter of air in the system, more likely would be a bad brand new temp sensor. Did you use a factory Volvo one? The factory ones are only so good and the aftermarket ones are a complete crap shoot as to whether they will work or not.

Mark

Problem seems to be solved, its been several hundred miles (500+) and a few weeks now with no check engine light. For all I can tell it seems to have taken care of itself, with the only thing being changed is that I unplugged the ECT sensor from the harness and twisted the exposed wires a few times before reconnecting. I did this thinking there could be some sort of possible external interference (similar to what happens with UTP cat 5 cable) when the wires run parallel and exposed.

The new temp sensor was an FAE brand (made in Spain), and the electricial resistance (Ohm) vs. temp checked out according to spec.

Thanks again for the suggestions and tips.

Zack
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Zack Silver 83' 242Ti (230k)