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Old 03-05-2021, 09:55 PM   #1
Steve Beswick
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Default 1994 945 - fan runs constantly, CEL, flash code says coolant temp sensor ...

... But I have replaced the sensor twice. The last sensor measured 2.23k ohms across the terminals at room temperature. How can I test the wiring? Iím assuming test for continuity from connector to the ecu, but I donít know what pins on the ecu, and to be honest Iíve never looked for the ecu itself. Where is it? I have been poking at this pod and on for the last year as I can during my chaotic life, and if I canít fix it soon Iím going to need to get rid of the car, which I really donít want to do. Please help!
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Old 03-06-2021, 01:49 AM   #2
Acke
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The ECU is in behind the kick panel in the passenger footwell. Pin 13 is for ECT.
https://ipdown.net/wiki/index.php?title=LH_2.4_Jetronic

A wiring fault could be quite possible since the fan runs constantly if the ECT sensor connector is loose/unplugged.
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Old 03-06-2021, 11:00 AM   #3
bobxyz
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Make sure you have the correct sensor for LH2.4. The LH2.4 sensor actually contains 2 separate sensors, with each sensor being connected between a pin and the grounded body. The similar LH2.2 sensor also has 2 pins but connects a single sensor across the pins with no connection to the grounded body.

To check, unplug the sensor and measure the resistance from each pin to the block. Each should be ~2K ohms at room temp. Across the pins should be ~4K (2K to block and 2K back to 2nd pin).
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Old 03-06-2021, 11:18 AM   #4
PCH
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Measure the sensor from the ECU plug side. This way you know the wiring and connections are good. ECU itself can be faulty too of course.
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Old 03-06-2021, 02:07 PM   #5
Steve Beswick
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Quote:
Originally Posted by bobxyz View Post
Make sure you have the correct sensor for LH2.4. The LH2.4 sensor actually contains 2 separate sensors, with each sensor being connected between a pin and the grounded body. The similar LH2.2 sensor also has 2 pins but connects a single sensor across the pins with no connection to the grounded body.

To check, unplug the sensor and measure the resistance from each pin to the block. Each should be ~2K ohms at room temp. Across the pins should be ~4K (2K to block and 2K back to 2nd pin).
I ordered the second sensor from IPD. Are they known for making this sort of error?
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Old 03-07-2021, 02:27 PM   #6
DET17
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On the 9 series fan control, the 3 sources for triggering the fan relay (all with a ground path to fire the relay) are the ECU output (coming from your head mounted temp sensor), the high pressure on the AC condenser (will trigger the HIGH speed) and the standard pressure on the AC condenser (AC is ON, calling for low speed fan speed).

Any broken wire will create this same ground path and result in your fan running constantly ..... but since the fan relay block is powered off the battery with a fusible link, it would run even if the car were shut off.... so that isn't likely. You can prove this latter point to yourself by studying the schematic, also by grounding those small inputs to the bottom of your relay. If your car is a turbo, the relay lives right in front of the battery.

Good luck! You need proper fan control to protect that aluminum head on the iron redblock.
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Old 03-08-2021, 08:01 PM   #7
Lazarus
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Which speed? High or Low speed? If the fan runs all the time, either the fan relay has arc welded itself together, or one of the relays is getting a contstant signal to its operation coil. These are 12 volt relays so measure both relay operation coils to see if the relay(s) are being told to fire.

-L
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Old 03-09-2021, 10:19 PM   #8
Steve Beswick
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Hey everyone, just thought I’d report back on this.

To clarify, in case I didn’t say it before - the original sensor was accidentally destroyed during a head gasket replacement. That’s a story all in itself, but I’m pretty sure the PO used every bit of Alumaseal he could find on that thing, because there were 4 water passages open in the entire head. The sensors were left in while drilling the “filler” out, to avoid accidentally damaging where the sensors mounted, but the sensors got drilled instead. Whoops!

So I bought a sensor from rock auto, and it turned out to be the wrong one.

Deciding I didn’t want to mess around, I bought a sensor from IPD, assuming they would get it right. As it turns out, nope. Got the wrong one.

So I bought the one in stock at the Oriely’s on the other side of town, and now my Volvo runs the best it has since I bought it in 2017. Go figure.

Thank you so much to everyone for your help!
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