Coolant Temp Sensor...

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.
1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
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rspi
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Coolant Temp Sensor...

Postby rspi » Mon Jul 16, 2012 3:32 pm

Ok, I'm getting confused. Is this the engine coolant temp sensor that causes the car to have hard starts? I thought this also sent the temp signal to the ECU and gauge in the dash?
http://www.fcpeuro.com/products/volvo-e ... 90-9186486

Image

The sales page indicates it's purpose is to control the fan. :?
'95 855 T-5R, Panther - 22/28 mpg
'98 S70 GLT, Lil' Red
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Volvo's of past: '87 740 GLE, '79 262C Bertone, '78 264, '95 960, '97 960, '98 S90, '98 S70 GLT, '95 850 T-5R Yellow
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jimmy57
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Re: Coolant Temp Sensor...

Postby jimmy57 » Mon Jul 16, 2012 3:43 pm

Beginning with the 850's and then on all new model Volvos since, the engine has one coolant temp sensor. The sensor is wired directly to the ECM. The ECM controls the fan for engine temp and sends a signal to the cluster and to the climate control if car has ECC.
Cluster uses the signal for gauge. ECC uses it to regulate a nicer programmed feature to blow windshield with lower blower until water temp gets warm enough to feel nice on our feet at which point a transition form defrost to floor in a few stages occurs (assuming you have fan and mode both on "AUT".

rspi
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Year and Model: 850 T-5R Wagon
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Re: Coolant Temp Sensor...

Postby rspi » Mon Jul 16, 2012 3:50 pm

Good. It threw me a little when they called it a "Engine Coolant Fan Temperature Switch". I got one from FCP about a month ago and it has already failed. Left my daughter stranded with a dead battery. :x
'95 855 T-5R, Panther - 22/28 mpg
'98 S70 GLT, Lil' Red
--------------------
Volvo's of past: '87 740 GLE, '79 262C Bertone, '78 264, '95 960, '97 960, '98 S90, '98 S70 GLT, '95 850 T-5R Yellow
Donate Today - Volvo Repair Videos

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jimmy57
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Re: Coolant Temp Sensor...

Postby jimmy57 » Mon Jul 16, 2012 4:59 pm

When the sensor fails you get a 6 minute (varies a bit on some models) afterrun of the engine cooling fan. Did 6 minutes of fan running kill the battery?

byeboy
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Re: Coolant Temp Sensor...

Postby byeboy » Mon Jul 16, 2012 5:04 pm

I'd like to suggest that what the failure was is the two wire connection plug. If the sensor is not completely and properly connected, it causes the fan to run in default "high" mode, plus run for six minutes after engine shut down. (Your daughter probably would not ave noticed this). Separate the plug, slide the plastic parts down the wires, use baking soda paste to clear out any corrosion (mine had plenty down in the lower "tube" parts), and use bulb grease or vaseline on the connection to keep corrosion at bay.

I know this because I experienced exactly the same thing, and used my AAA to tow me back home, at which location JImmy57 zeroed in on the cause...'been doing great since then.

That fan draws heavy amps. I had my three year old battery checked, and its still in very good condition, so the amp overnight charge was all it needed to make it happy again!

rspi
Posts: 6170
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Year and Model: 850 T-5R Wagon
Location: Albuquerque, NM
Flag: United States of America

Re: Coolant Temp Sensor...

Postby rspi » Mon Jul 16, 2012 5:20 pm

jimmy57 wrote:When the sensor fails you get a 6 minute (varies a bit on some models) afterrun of the engine cooling fan. Did 6 minutes of fan running kill the battery?


I think it ran longer than that but maybe that was it. The problem is that her normal commute to work is only 3 miles, about 8 minutes so the battery is likely 1/2 drained anyway. So you drive 8 minutes, cut the car off, then the fan runs for 6 minutes, that'll kill any battery.

I got one out of a junked car and all is well.
'95 855 T-5R, Panther - 22/28 mpg
'98 S70 GLT, Lil' Red
--------------------
Volvo's of past: '87 740 GLE, '79 262C Bertone, '78 264, '95 960, '97 960, '98 S90, '98 S70 GLT, '95 850 T-5R Yellow
Donate Today - Volvo Repair Videos

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jimmy57
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Year and Model: 2004 V70R GT, et al
Location: Ponder Texas

Re: Coolant Temp Sensor...

Postby jimmy57 » Mon Jul 16, 2012 6:03 pm

Byeboy's post covers a VERY common failure on 850/S70/V70 gen 1/ c70 gen 1
The terminals in the plug that goes to the pigtail on the ECT sensor are potted with a clear plastic that disintegrates. You plug it together but the plastic that should be positioning the terminals in the grey (maybe black) connector body are crumbled and the terminals don't actually end up slid onto the bullet terminals in the pigtail.

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cn90
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Re: Coolant Temp Sensor...

Postby cn90 » Mon Jul 16, 2012 6:13 pm

Interesting! I still have the original ECT and car runs fine at 120K miles.

Question: is this a problem with the ECT itself or the Connector?
1998 S70 GLT 160K+
2005 XC90 2.5T 85K+

byeboy
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Joined: Mon Sep 05, 2011 6:48 pm
Year and Model: 850R, 1997
Location: Texas

Re: Coolant Temp Sensor...

Postby byeboy » Mon Jul 16, 2012 6:30 pm

cn90 wrote:Interesting! I still have the original ECT and car runs fine at 120K miles.

Question: is this a problem with the ECT itself or the Connector?


Well, all good hope rides with it being the connector...and cleaning it is free ad easy...so think of that as Step1! The dried "stuff in the lower tbe parts was like candle wax...wood Skiskabob Skewer worked well to push it out, and clean up the bore. :)

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j_cd
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Year and Model: 1998 S70 GLT
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Re: Coolant Temp Sensor...

Postby j_cd » Mon Jul 16, 2012 11:36 pm

Interesting. I replaced my thermostat recently, as it was acting sluggish. I was going to replace the ECT sensor at the same time, but my intake manifold spacer pushes the manifold out just far enough to make it impossible to get a wrench on the sensor. After reading this thread, I'm not sure whether or not I should replace it when I have the manifold off for this valve job. The original is still working perfectly. The replacement part I have is the aftermarket one from fcp. It looks fine, but who knows.


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