Modern vehicles, their thermostats, and P0128

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Originally Posted By: SteveSRT8
PO128 is a code set when your vehicle does not reach operating temp in a prescribed period of time for 3 trips. About ten minutes IIRC.

3 good trips will shut it off by itself, no intervention needed. It's not something that requires a lot of worrying...


From the FSM:

Thermostat Monitor

The thermostat monitor is designed to verify correct thermostat operation. This monitor is executed once per drive cycle and has a monitor run duration of 300-800 seconds. If a concern is present, diagnostic trouble code (DTC) P0125 or P0128 is set and the malfunction indicator lamp (MIL) is illuminated.

The monitor checks the engine coolant temperature (ECT) or cylinder head temperature (CHT) sensor to warm up in a predictable manner when the engine is generating sufficient heat. A timer is initialized while the engine is at moderate load and the vehicle speed is above a calibrated limit. The target timer value is based on ambient air temperature at start-up. If the timer exceeds the target time and ECT or CHT has not warmed up to the target temperature, a concern is indicated. The test runs if the start-up intake air temperature from the intake air temperature (IAT) sensor is at, or below the target temperature. A 2-hour engine OFF soak time is also required to enable the monitor and to prevent erasing of any pending DTCs during a hot soak. This soak time feature also prevents false-passes of the monitor when the engine coolant temperature rises after the engine is turned OFF during a short engine OFF soak period.

The target temperature is calibrated to within 11°C (20°F) less than the thermostat regulating temperature. For a typical 90°C (195°F) thermostat, the target temperature would be calibrated to 79°C (175°F). Some vehicle calibrations may lower the target temperature to less than 27°C (50°F) for vehicles that do not warm-up to thermostat regulating temperatures in the 11°C (20°F) to 27°C (50°F) ambient temperature range.

Inputs: ECT or CHT, IAT, engine LOAD (from MAF sensor) and vehicle speed input.
Typical monitor entry conditions:

vehicle speed greater than 24 km/h (15 mph)
intake air temperature at start-up is between -7°C (20°F) and target thermostat temperature
engine load greater than 30%
engine OFF (soak) time greater than 2 hours



The conditions for this code are calibrated. What do you mean by "3 good trips will shut it off by itself, no intervention needed." You can't set this code through 'bad' trips. If the code sets, there's a definite malfunction.

My work commute is 15 miles one way, all 2 lane highway. How could I have eliminated this without intervention?
 
I had that same code a couple of month ago in a Sienna.
The ambient dip to 40F from 80F the day before.
I cleared the code and never come back but I changed the t-stat anyway in preparation for winter.
At least it was a nicer weather to do the work.
As usual, in TX, the temperature went back up to 70-80F so that probably will be fine.

I wish part can last forever but t-stat is mechanical and the spring do wear out after 230K miles.
 
I guess it depends on the manufacturer, but in my Mazda 3 the code was set long before any malfunction could be detected on the coolant temp. gauge. I reset it the first time and it came back within a week or so. I then changed the thermostat and re-set the code.
I don't know if the CEL would go off by itself after changing the thermostat though.
 
they wear out just as they have always done.modern pcm programming just tells you about it sooner.
on the old tbi chevys i would notice the gauge swings and know it was headed south.if i waited too long i would start seeing high temps on the first open cycle.that meant change it now!most stuck open.that would set a code.but it has a real gauge.
many newer vehicles have a "dummy light"gauge.i hate those.no trends to see.i want real instruments!
 
So, I've had no problem resolving this code in the past.


However, I replaced the t-stat on Tues evening. Unlike before, temp does indeed rise to op temp, and seems to do so in a reasonable amount of time. Yet, the MIL has yet to turn off...
The service manual is unclear as to the conditions required for turning off the light. I've taken the car between the house and work 5 times since replacement. Car warms up just fine, verified by watching the live data on the scanner

Anyone know what the PCM needs to see to satisfy p0128?
 
Originally Posted By: emmett442


The conditions for this code are calibrated. What do you mean by "3 good trips will shut it off by itself, no intervention needed." You can't set this code through 'bad' trips. If the code sets, there's a definite malfunction.

My work commute is 15 miles one way, all 2 lane highway. How could I have eliminated this without intervention?


3 trips within the parameters set by your mfgr will erase the code. Simple as that. And it took 3 repetitions of the malfunction to set the code. It does not immediately trip the MIL.

Note that minor variations by mfgr are normal, each has their own ideas on this one...
 
Have you satisfied all the parameters of the self test running? The one I have trouble with if the car is sitting outdoors this time of year is the entry temp. It has to be above 20 Degrees for the test to initiate, and right now, after satisfying the 2 hour cold soak minimum, the intake temp generally isn't over 20 (nine degrees out at the moment), so the test doesn't run. Just a thought...

Personally, I prefer to reset the code, and if it does not come back, then I am satisfied.
 
es, Ive replaced multiple thermostats in Crown Vics for this same issue. Usually I catch them because they are running in the 170-180F region on the highway. So Ive been making it a regular maintenance item that I replace at about 3 years along with drain and fill radiator with fresh coolant.
 
Originally Posted By: MNgopher
Have you satisfied all the parameters of the self test running? The one I have trouble with if the car is sitting outdoors this time of year is the entry temp. It has to be above 20 Degrees for the test to initiate, and right now, after satisfying the 2 hour cold soak minimum, the intake temp generally isn't over 20 (nine degrees out at the moment), so the test doesn't run. Just a thought...

Personally, I prefer to reset the code, and if it does not come back, then I am satisfied.


Not sure if the parameters were satisfied - I couldn't find a solid definition of them in the service manual. It stated that it needs a certain air temp, time, and a cold soak, and drive cycles, but didn't give anything that could be quantified. No numbers.

That said, Friday night I cleared the code and it has not returned. Temp is now rock steady at 90C, much better than before.
 
Originally Posted By: Colt45ws
es, Ive replaced multiple thermostats in Crown Vics for this same issue. Usually I catch them because they are running in the 170-180F region on the highway. So Ive been making it a regular maintenance item that I replace at about 3 years along with drain and fill radiator with fresh coolant.


Perhaps not a bad plan.
 
I think the only one you didn't have was the drive cycles required. Otherwise, the parameters were in the FSM (and are the same for my '07 Explorer with the 4.6).

vehicle speed greater than 24 km/h (15 mph)
intake air temperature at start-up is between -7°C (20°F) and target thermostat temperature
engine load greater than 30%
engine OFF (soak) time greater than 2 hours

The tough one at the moment is #2 (at least around here). That's why I do the full reset instead of waiting for it to clear.

Will be doing the thermostat on the Explorer soon - temp has gotten lazy and floats down to 180 way to easy at the moment.
 
Originally Posted By: MNgopher
I think the only one you didn't have was the drive cycles required. Otherwise, the parameters were in the FSM (and are the same for my '07 Explorer with the 4.6).

vehicle speed greater than 24 km/h (15 mph)
intake air temperature at start-up is between -7°C (20°F) and target thermostat temperature
engine load greater than 30%
engine OFF (soak) time greater than 2 hours

The tough one at the moment is #2 (at least around here). That's why I do the full reset instead of waiting for it to clear.

Will be doing the thermostat on the Explorer soon - temp has gotten lazy and floats down to 180 way to easy at the moment.


Ah, I think you are right there. Intake temp would have been a problem last week.

Thanks!
 
Oh, I had a random memory come to mind to day. I had read an article about DexCool and the Ford Mod motors was specifically called out for not being compatible with it. IIRC, it gave a reasonable explanation of why.. Im going to hunt that article down.
 
Found it! Darn, aren't I the greatest?

http://articles.sae.org/8242/

Quote:
Unlike silicates and phosphates, which deplete as they go to work coating the cooling system, OAT-alone formulas have very long service life. But OATs work very slowly, perhaps taking over 5000 miles to form a protective oxide surface. So they are unable to provide the fast re-protection of cavitation-pockmarked surfaces in water pumps.

If a cooling system is prone to cavitation and the vehicle is used in the kind of load service that is conducive to it, the pockmarking increases and can corrode, affecting water pump service life. As a result, Ford has continued with the yellow S-HOAT on the older 4.6-L and 5.4-L V8s and will not change, as these engines are planned for phase-out.
 
Originally Posted By: Colt45ws
Found it! Darn, aren't I the greatest?

http://articles.sae.org/8242/

Quote:
Unlike silicates and phosphates, which deplete as they go to work coating the cooling system, OAT-alone formulas have very long service life. But OATs work very slowly, perhaps taking over 5000 miles to form a protective oxide surface. So they are unable to provide the fast re-protection of cavitation-pockmarked surfaces in water pumps.

If a cooling system is prone to cavitation and the vehicle is used in the kind of load service that is conducive to it, the pockmarking increases and can corrode, affecting water pump service life. As a result, Ford has continued with the yellow S-HOAT on the older 4.6-L and 5.4-L V8s and will not change, as these engines are planned for phase-out.



Cool, thanks for the info.

But, I can't argue with success. My 3rd modular with Dex in it (other 2 were f150's - 100k on one 4.6, 215k on the other 5.4)- nothing negative to report to date. Not sure what it would take to create any problems, but apparently I would have to go out of my way to do so - and at that point, I don't think I could put any blame on the coolant!

I think I'll be fine
smile.gif
 
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