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Old 12-15-2013, 02:31 AM   #1
Frost462
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ECT sensor or switch??

Between 3 separate mechanics, the guy at Ford and the internet, I am confused and frustrated. I need help! I have a 2005 Focus ZX3 2.0L. My engine light came on and it's giving me P0128 as a code. (Coolant Temperature Below Thermostat Regulating Temperature). My car is not overheating, and the gauge works. Heater blows hot air. My antifreeze is new and full. I replaced the "engine coolant temperature SWITCH" (this is what the guy at Ford called it) that is in the middle of the valve cover. No change. Two people told me to change the "engine coolant temperature SENSOR, located vaguely behind the engine (somewhere) on the passenger side. Can't locate this mystery sensor, but Autozone sold me the part. I would at least like to know if this mystery sensor even exists, and if so, WHERE IS IT?? I really don't want to have to change out the thermostat if that's not the problem because I REALLY don't want to remove the intake manifold to get to it.... Any advice is helpful...


 
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Old 12-16-2013, 11:51 PM   #2
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I think the confusion arises because you haven't confirmed your engine type, though I think for that year it must be a Duratec of some type - 2.0 or 2.3 L. The 2000 - 2004 Zetec engined car (non-SVT) has a CHT (cylinder head temp) sensor at the passenger rear side of the cylinder head near the alternator.

The 2005 - 2007 Duratec engined car has a sensor in a different location, in the middle of the cover possibly; don't know for sure because I don't own one, so someone with a Duratec car may need to chime in.

Also this only applies to North American cars. You haven't stated where you're from and European cars could be different again - many more engine options overseas.

Temp sensors don't fail that often; thermostats get stuck open more frequently and that may cause your car not to reach operating temp. since coolant is always flowing through the rad unrestricted.
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Old 12-17-2013, 09:36 PM   #3
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It may even possibly be as simple as sensor unhooked. Computer is reading 5 volt reference, cause it has no pull down to ground. As engine warms, it would have less resistance that would allow less voltage because more would be going to ground.
For instance as it warms maybe only 2 volts left for computer to sense.
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Old 12-17-2013, 10:38 PM   #4
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P0128 is the thermostat monitor. Replace your thermostat, it's stuck open.
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Old 12-18-2013, 07:57 AM   #5
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Quote:
Originally Posted by paulg127 View Post
P0128 is the thermostat monitor. Replace your thermostat, it's stuck open.
He says he has hot air.
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Old 12-18-2013, 09:09 AM   #6
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Quote:
Originally Posted by mmurphy View Post
He says he has hot air.
You can still have hot air with the thermostat stuck open if the engine is still getting up to operating temperature. Just because the thermostat is stuck open doesn't mean the coolant is going to be cold all the time. However, that being said, it usually takes a bit longer for it to reach operating temps. And you will usually see the temp gauge moving as you stop and go. While you are moving at higher speeds it will usually drop. When you are stopped it will usually rise back up.

If your weather is -0 then you will really see a difference and you may not have the hottest air.
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Old 01-04-2014, 01:51 PM   #7
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Quote:
Originally Posted by GhostTribute View Post
You can still have hot air with the thermostat stuck open if the engine is still getting up to operating temperature. Just because the thermostat is stuck open doesn't mean the coolant is going to be cold all the time. However, that being said, it usually takes a bit longer for it to reach operating temps. And you will usually see the temp gauge moving as you stop and go. While you are moving at higher speeds it will usually drop. When you are stopped it will usually rise back up.

If your weather is -0 then you will really see a difference and you may not have the hottest air.
Ghost, I had the ECT sensor (the one on top of the head) replaced following a P0128 readout. After replacement, I noticed the gauge never got above cold reading during an early morning (30 degree) drive. Later, the gauge started moving but did so as what you're describing- normal at low speeds, cold at high speeds. From what you're saying sounds like the thermostat needs replacing???
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Old 01-04-2014, 09:53 PM   #8
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Yes the thermostat is the usual suspect for that type of situation.
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Old 01-05-2014, 05:53 PM   #9
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I just replaced mine.
drain rad mine has a cross a flat head screw driver fits in.
1.Jack up pass. side take off shroud 2 10mm bolts to get at serpentine belt tensioner
2.remove serpentine belt 15 mm to release tension
3.take off power steering pump 4 10mm bolts on mine top 2 bolts hold the power steering reservoir on fluid will leak.The two on bottom 1 is behind a steering line and a 10mm ratchet wrench would make it go faster.
4.remove 2 hoses I used channel locks on hose clamps and a pry bar to get hoses loose
5. 3 8MM bolts to remove the thermostat housing.
There are 2 thermostats available from Ford one with a sensor and one without. Mine was without sensor

Last edited by autolite; 01-05-2014 at 09:48 PM.
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Old 01-05-2014, 06:58 PM   #10
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Very cold temps can cause this to happen and nothing is wrong , it could all be how the stock tune is set and what the temps are out side

Tuning cars I see this a lot

Tom
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