P0128 2009 Ford Fusion

Mikerizer

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#1
Make
Ford
Model
Fusion
Year
2009
Miles
120,000
Engine
2.3L
2009 Ford Fusion, 2.3L, 120k miles

CEL is on...the code is P0128. The engine is running good, the temp needle on the dash is halfway between hot/cold, right where it should be.

Are there two coolant sensors? One for the needle, and one for the computer? Where do I need to look for this specific sensor, to check for connectivity, and/or replace?

NOTE: The code originally set on June 19, and I cleared it. It came on again today, same code.

Thanks!
 
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#2
P0128 is a relatively common OBDII trouble code. It is triggered when your Ford Fusion‘s coolant temperature fails to reach the proper operating temperature.



It’s a generic powertrain code, which means that regardless of who manufactured the vehicle, it’ll have the same meaning (1996+).


Fusion P0128 Symptoms

There aren’t many symptoms with P0128, unless it gets cold. Here are the symptoms associated with this trouble code:

  • Lack of heat– The biggest symptom of the P0128 trouble code in the Ford Fusion is going to be lack of heat. When the thermostat doesn’t bring the engine all of the way up to the proper operating temp, it means that the water going through the heater core isn’t as hot. This leads to less/no heat.
  • Service Engine Soon– Other than the heater not working as good, the only other symptom of P0128 is typically the service engine soon light itself.


P0128 Causes: Ford Fusion



Fixing P0128 is usually a pretty easy thing to do, since 90% of the time it’s going to be the thermostat that is throwing the code. Here are the most common causes of P0128:



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  • Thermostat Stuck Open– Far and away, the most typical cause for the P0128 code is going to be a thermostat that is stuck open. When a thermostat is stuck open, it allows coolant to flow through the engine at all times. When this happens, the engine is “overcooled” and never reaches the proper operating temperature. How to Replace a Thermostat (video). Fusion Thermostat
  • Wiring– If the thermostat itself isn’t the problem, it’ll be the wiring/sensor associated with engine water temp detection, or the coolant temperature sensor itself.
  • Dan Moon's additional comment...P0128 is sometimes stated "Engine failed to reach operating temperature within timeframe." Meaning "it took TOO LONG to warm up".
 

billr

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#3
I would use live-data to check what ECT the PCM is reading, then check that against an immersion thermometer. A poor connection in the wiring to most ECT sensors results in a low reading; so that must be considered as well as the t-stat
 
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#4
Got that code on my Hyundai Elantra, and the temperature gauge was reading normally, problem was the thermostat wasn't closing fully taking it longer to warm up. Dealer repaired it under warranty, ha ten years or 100K miles on this thing, thermostats are not a couple of bucks anymore, more like 80 plus labor.
 
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#6
Another relatively new problem is adding an electric heater to the thermostat, debatable why they are doing this. Some claim the vehicle switches this heater on if you step on the gas so the heater turns on first to open the thermostat because the engine will heat up more.

I really doubt this, because you can only do this for a few seconds, other reasons are that the engine runs more efficient with higher or lower temperatures depending on speed, doubt this as well, usually only around a 20*F difference, and temperature percentages are based on absolute zero around -460* F, a 20 degree change is very small.

Key reason that make sense is to rush production, you can't add coolant to any engine until the thermostat is open, a 25 watt heater on that tiny wax bellows does this very quickly, and with the new stuff, like switching on the ABS pump, has to be done with a way overpriced scanner on the diagnostic plug.

As it is controlled by the ECU or whatever they call this computer box now I found a problem by connecting my digital oscilloscope to the starter circuit. When hitting the starter switch, the battery voltage drops to below 8.5 volts, and since they are stilling using a 7805 voltage regulator designed back in 60's with a mininum of a 3.5 volt drop, the microcontroller chip drops below 5 volts so does not get a proper power on reset.

Starts reading erroneous codes, in this case, the only thing it does is kicks on the thermostat heater, others can be anything from the AC system not working, engine won't start, radio won't go on. Using the voltage drop method, found a weak ground connection, cleaned it up and all was good again.

Really a stupid idea was Boeing adding a software based microcontroller to their 737 Max trim circuit, one bit short or extra, confuses the processor and it crashes as well as the rest of the plane, only stupid kid engineers would do something like this. But when microprocessors were added to our vehicles, driving everybody nuts.

Been told my marketing a zillion times, use an 89 cent microcontroller, that is what we paid for them, you pay around a thousand or so, you nuts, if it crashes, so will the vehicle.