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Old 06-20-2010, 09:33 AM   #1
p58ff
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P0125 code, temp gauge stays low...

Hello all. Well, I've got a 2002 SPI Auto LX Focus. Just recently the temp gauge has been staying lower than usual and it finally returned the P0125 code.

I searched the FF site and got tons of returns. Looks like the most likely cause is the coolant temp sensor that mounts in the thermostat housing. (Another question about that in a minute.)

I replaced the sensor and the code still comes back. I figured that maybe the thermostat is bad so I removed it and tested it, boiling water, and it opened fine and closed with the application of cold water.

Any ideas as to what to look for next? Is there another sensor that I am missing?

No leaks, fans running and kicking in with A/C, resistor/thermal switch look OK. It does not overheat but I do think the car is running a little 'off'. Cannot put my finger on it but I feel like it might be a little sluggish.

Now, about the thermostat housing. It looks like the thermostat and housing are one entire assembly but the info that I come up with says differently. My housing has the small hose and larger hose outlets up front and a medium size outlet at the back. Three bolts and the coolant temp sensor mounting hole. What do you guys see on your 2002's?

Thanks.

Brian


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Old 06-20-2010, 09:39 AM   #2
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It varies with engine, but my temp sensor is in the cylinder head between plugs 2 and 3. It is called a cylinder head temp sensor. The one in the thermostat is for control of the cooling fans I believe.
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Old 06-20-2010, 11:59 AM   #3
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Niggly - From what I've heard here, I think the SPI uses the older style water temp sensor that sticks into the coolant as opposed to the cyl. head temp sensor on newer designs...

OP - Just when do the fans run, only both with A/C or does one or both kick on at other times...
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Old 06-20-2010, 12:34 PM   #4
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Both fans on with A/C engaged; fan speed seems to 'step-down' while still running after A/C is turned off and finally stop. Not sure if the fan on the drivers side stopped or kept running. Temps here yesterday were upper 80's and I had taken a test drive of about 5 miles. The CEL lamp is still off as of this morning but I've only driven about 20 or so miles since yesterday.

Brian
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Old 06-20-2010, 02:02 PM   #5
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Well, just have to see what happens with more time - As long as coolant is full, the system may have "purged" itself now, and hadn't the first time the code recurred. Keep an eye on temp, and note when which fans turn on if it stays abnormal - if normal now I'd say you found the problem...
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Old 06-26-2010, 09:11 AM   #6
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Still setting a code darn it....I am beginning to think there may be a wiring problem...maybe a bad connector.

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Old 06-26-2010, 09:36 AM   #7
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The P0125 code:
"This means that the engine coolant temperature (ECT) sensor indicates that the engine has not reached the required temperature level to enter closed-loop operation within a specified amount of time after starting the engine."

From this it appears that the ECU takes it's fuelling data from the rate of coolant heating and any reading out of the specified range throws a code. I'm guessing that something is stopping or appearing to stop, the coolant getting hot enough in the required time. The possibilities could be:
1) Faulty water pump- slow circulation.
2) Thermostat temperature too low.
3) Faulty thermostat.
4) Faulty sensor.
5) Incorrect sensor- wrong temp profile.
6) Wiring problem......maybe.

Just my thoughts....
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Old 06-26-2010, 01:03 PM   #8
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Yeah, this one is an odd duck.

It does not over heat so I would surmise it's not a water pump. Thermostat is original from Ford. I 'boiled' the thermostat and it opens and then closes with cold water application. Sensor is new...I would hope the profile would be correct. I was just guessing about the wiring. I may find a crashed Focus and lop off the connector and re-splice it into my harness.


Maybe if I just put black tape over the CEL........

Thanks for your suggestions.

Brian
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Old 06-26-2010, 02:20 PM   #9
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i would replace the thermostat the temp that it open at is what you are looking for. Ive seen bad thermostats open in boiling water but they open so soon that the engine takes too long to get to operating temp hence the cel. the ecu only gives the engine a set amount of time to get to operating temp if it doesn't it it set the code. thermostats are cheap and don't last much longer than 50,000 miles anyway.
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Old 06-26-2010, 02:58 PM   #10
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Yeah, I can try that I suppose. Need to find the correct 'stat as the one in there looks like it is a one-piece affair; the housing and thermostat are a unit. 50K miles..well got that beat by 100K! HA!

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