[SOLVED] 1999 S70 GLT, coolant temperature P0116 code, radiator fan and throttle module stay on after egnition is off Topic is solved

[z80]

Hello!

The car is 1999 S70GLT. It has developed the following symptoms. Would you please be so kind to give me an advice?

1) P0116 code "engine coolant temperature sensor range".
2) Radiator fan starts even when the engine is cold and stays on when ignition is off. It turns off quite some time later.
3) Throttle module stays on after ignition is off. It keeps wining for quite some time but eventually shuts down probably together with the radiator fan. Are they paired together in some way?
4) Dashboard temperature readings are all ok and as usual. Temperature needle starts low and slowly climbs to the middle of the range while I drive the car.

Internet says that the temperature sensor under the thermostat has failed. But why do dashboard temperature readings look as usual? Is there a separate sensor for the dashboard?

Is there a specification for the temperature sensor resistance I could check to confirm it's bad to make sure it is not the wiring what has failed?

I'd appreciate any information! Thank you!

[abscate]

The 1999 coolant temperature resistance specs are here, the table is formatted badly, shift the cells so thst temp and resistance are aligned

[scot850]

I would check the connector for the coolant temperature sensor for corrosion or bad wires. It is usually mounted at the back of the power steering pump. The fact the temp gauge gets to the 3 o'clock position would point to it is sensing correctly, but the signal is not correct to the fan or fan relay. I would also check the relay connectors on the top of the radiator just under the shroud.

Neil.

[z80]

The 1999 coolant temperature resistance specs are here

Thanks a lot! Just checked the resistance on the fully warmed up car. On sensor socket terminals the resistance is 18.3 kOhm. This number seems to be much more than 318 Ohm in the table.

But still how does the dashboard gets correct readings? 18.3 kOhm seems to be well below absolute zero...

I would also check the relay connectors on the top of the radiator just under the shroud

Thank you for the suggestion! I did check all 3 plugs going into fan relay. They seem to be fine, no corrosion. I also probed the middle one (with two thin yellow wires) with a multimeter. It seems it does indeed signal the fan to stay on.

[scot850]

If you plan to replace the coolant temp sensor (ECT) normally we only recommend the OE Volvo part. Some have had some success with aftermarket pats but they number in the handful.

Neil.

[z80]

It is strange. With the car cooled down I've re-checked the resistance and it seems to be at around where it should be. I read 1012 Ohms, the engine feels warm on touch. And the resistance according to the table is between 20C and 30C.

I'm going to re-check hot resistance again to make sure it really goes to kilo-ohms range and it wasn't just a bad contact when I measured last time...

If you plan to replace the coolant temp sensor (ECT) normally we only recommend the OE Volvo part. Some have had some success with aftermarket pats but they number in the handful.

Neil.

Thanks a lot for the hint! As soon as I confirm the sensor failure, I'll make sure I pick OE part.

[z80]

I've re-taken the measurements in the morning after the car has been cooling down overnight.

Cold engine: R=3330 Ohm.
Hot but thermostat closed: R=350 Ohm.
Hot, thermostat open: R=224 Ohm.

It kept holding fan on for a long time up until I've erased the error code. After that the car seems to got back to normal. The fan only turns on when it is hot and thermostat is open and stays on for ~30 seconds at a time.

So I cannot reproduce those 18 kOhm resistance I measured yesterday anymore. The error code doesn't get back, at least not yet as of today...

I guess I'll be driving with a multimeter in the car for now just in case the problem gets back.

I appreciate all the hints and support! Thank you all so much!

[abscate]

It is easier to drive with a spare ECT and replace it next time. There are not any tolerances given on the resistance measurements but yours seem out of kilter.

[wizechatmgr]

I'd just replace it. You'll very likely get better gas mileage upon doing so.

Also, hit that sucker with non-conductive grease. These get nasty after a while without it. Could be there was some oxidation you cleaned off while reseating it.

[z80]

It is easier to drive with a spare ECT and replace it next time. There are not any tolerances given on the resistance measurements but yours seem out of kilter.

Yes you are totally right! I didn't actually convert Ohms to degrees C. If I do so based on the table I get 241 Ohms corresponds to approximately 63C. and 274 Ohms to around 53C. Resistance doesn't go any lower than 241 Ohms. Both 63C and 53C seems to be a little bit too low temperature for a fully open thermostat.

It doesn't seem to be too expensive anyway. I'll probably just replace the sensor (and the thermostat as a preventative routine) and see what happens.

I'd just replace it. You'll very likely get better gas mileage upon doing so.

Also, hit that sucker with non-conductive grease. These get nasty after a while without it. Could be there was some oxidation you cleaned off while reseating it.

That might be the case. I've been testing the car today and I clearly saw the temperature needle going up and down a few times after which it turned the code P0116 back again. But each time I jumped out of a car to measure the resistance it was never totally out of bounds. First time 274 Ohms and the second time 241 Ohms.