2009 2.3 Temp-Gauge, P0128 Trouble Code, AC Temp-Mixer not working. - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 12-26-2016
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2009 2.3 Temp-Gauge, P0128 Trouble Code, AC Temp-Mixer not working.

As the title states, I have a 2009 2.3 Ranger thats just ticking over to 130k miles. I've been happy with her for the 3 years that I've owned her and for the most part she's been trouble free.

Last winter 2 issues started manifesting rather simultaneously.
1; A check engine light related to the temperature sensor, as well as intermittent temperature-gauge function.

2; The A/C Blending started failing, where its only cold on Max A/C, and on anything else its entirely hot.
Based on the reading I have already done from some insightful threads here in this forum, the 2.3 Duratec does not have an ECT Sensor, but has a Cylinder Head Temperature sensor, and an ECT sender.

From what I have read, if the CHT sensor fails, it will not let the temperature gauge read, which it currently does not. Additionally, it is apparently able to affect the operation of the A/C Blending Unit.


The printout from my failed smog-test says error code

Quote:
P0128; Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
So while this says its the thermostat, I think that the p0128 code is a generic OBD code, and so the "Coolant Thermostat" failure might rather be implying there is a failed temperature sensor, since there's actually no sensor in the thermostat. Since my heater is working fine too, it would seem my thermostat is also operating normally.

Am I reading this right?

TL:DR
2.3 DOHC.
Temp gauge began failing with intermittent function.
Temp gauge is now "dead" hard pegged on cold (operating stable for last 8 mos)
Engine produces heat fine/ Heater works great.
A/C Blender function failed at approximately the same time.
Engine trouble code P0128.

Suspected Fault: CHT Sensor.

I can start just replacing these parts, but I'm more interested in understanding what these do so I can troubleshoot them accurately, and I really dont wanna rip out my dashboard to replace the AC blender unless its actually at fault.

Thanks in advance for any input, and thanks for the insightful answers already on this topic.

Cheers.
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Old 12-27-2016
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Thermostat have a "fail safe" built-in, so if they fail they are suppose to fail open, so no overheating.

Thermostat's purpose is to get engine coolant to 190degF as fast as possible and to keep it above that temp, for lowest emissions, best fuel economy and cleanest oil.

Radiator is there for "extra" heat and may or may not be used depending on outside temp.

Thermostat controls flow thru radiator.

So simple and easy test is to start engine cold and drive it for 3 to 5 minutes, then feel radiator hoses, if hoses are heating up with the engine then thermostat is open, and it shouldn't be, coolant is circulating thru the radiator and it shouldn't be.

It will generally take an engine 5 to 10 minutes to heat up engine/heater coolant to 190degF, depending on outside temp and engine load.

P0128, coolant below expected temp, is a timer based code, computer expects coolant to warm up to 190degF within a certain time, and stay at or above that temp.
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Old 12-28-2016
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Thanks for the reply RonD, and thanks for the explanation of what the components are supposed to be doing. I observed the temperature of the radiator hoses in my engine as well-warmed within 5 minutes of driving. Being that its winter and 30-deg F outside I dont think that the engine was at 190F that fast so I changed the thermostat.

The accessibility was pretty good so it was only a 30-min swap, thankfully.

The temperature gauge is still not reading however, and based on what I'm reading that could be either the CHT-sensor or the ECT-sender.

My understanding is that the CHT-sensor tells the ECU what the temperature of the engine (cylinder head) is and the ECT-sender sends that information to the gauge?

Since my gauge has been pegged at below-cold for sometime despite normal operation, perhaps it is more likely the ECT-sender failing to activate the gauge?

I believe I have read of people testing voltages or resistances of temp-sensors to test them which I have never done, but am comfortable with the concept despite not knowing the proper method. I'll dig into how I might do that to more accurately troubleshoot the sensors instead of just replacing them.

Thanks again for the response.
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Old 12-28-2016
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2009 Ranger will have digital dash gauges, so engine temp comes from computer, no connection to the engine at all.

And I can't find an ECT(engine coolant temp) sensor on a 2009 Ranger 2.3l wiring diagram, or 2007.

CHT(cylinder head temp) sensor seems to be all it uses, and it goes directly to computer.

You can test digital dash gauges by using "Engineering mode", AKA "Dealer mode", to see if they are getting power and move full range
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Old 12-28-2016
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Quote:
And I can't find an ECT(engine coolant temp) sensor on a 2009 Ranger 2.3l wiring diagram, or 2007.
From what I understand, and I dont have a manual (yet) so I'm likely wrong, the 2.3 Duratec has a ECT/ *sender* not sensor, and the CHT sensor.

This is the CHT Sensor that I've found at O'Reilly for the truck.
This is the "Coolant Temerature Sender" that I've found as well.

I haven't replaced them yet, but I'm trying to find all the tests I can do before making the swap. $40 in sensors isnt really a big deal to me, but knowing that doing so is going to fix the problem is what I'm aiming for.

I believe I've found the CHT sensor inbetween plug 2 and 3, but I cant seem to track down this Coolant Temp Sender, unless as you suggest, there actually isnt one.

I'm about to pull the trigger on the FSM/Wiring on ebay. Lookin at $80 shipped... Reckon it'll be good for the long term maintenance since I plan on keeping this truck for as long as it can drive.

Thanks again for the reply, I'll see if I can track down how to put it into "Engineering Mode."

EDIT:

I figured out the Engineering Mode, and pushed it through the GAUGES test a couple times. The Coolant Sensor did go from min to max each time, however unlike the other gauges, it stablized in the middle for a moment instead of a fluid down-up-down like the rest. I suppose this could be an intentional thing so that a certain range of inputs appear as centered "normal" temperature reading and the engineering test mode simply cycled through the range of its outputs. In anycase, it would appear that the sensor works.

Now the question is, does that mean the Coolant Temperature Sender is good because the gauge moved? Or is the Temperature Gauge not directly controlled *directly* by the CT Sender?

Last edited by unfrail; 12-28-2016 at 02:54 PM.
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Old 12-28-2016
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3.0l and 4.0l had senders and sensors both, yes sender is for dash gauge only
later model, 2007 and up, 2.3l dash shows no temp sender hookup, just oil pressure switch.

And only temp unit on 2.3l engine wiring shows CHT sensor to computer, it is also used for e-fan control as well, which I would expect an ECT sensor would be better to use "if it was there"

Ford does list it for a 2009 Ranger 2.3l, 10884 or SW-5174, but seems to be hit and miss on if Ranger actually has that unit.

If you can find ECT sender on heater or radiator hose fitting then you can test it's connection to the gauge.
It will be a two-wire sender but one wire is a Ground, test with OHM meter for that wire.
The other wire will go to the computer or gauge.
Use a jumper wire on that wire to a Ground, turn on the key gauge should go full HOT, unhook the wire and it should go down to COLD.
It can be visa versa
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Old 12-29-2016
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I couldnt find any ECT sender based on visual descriptions in other 2.3 posts.

I figured since the computer was throwing a warning about poor temperature data that it would have been the sensor that was the issue and not just the gauge. Replacing the sensor was a trivial fix and ended up resolving the issue as far as I can tell, since my gauge is working again.

Unfortunately it seems my A/C Blend Door is its own issue, regardless of coincidental failure. I reckon I can find plenty of existing threads on that fix already as it sounds pretty common.

Thanks for the comments RonD. Definitely was useful feedback.
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Old 12-29-2016
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take the ranger to a mazda dealership , that engine is mazda and they know where the 2 sensors are located
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