Help Po128 What Is It???

[JCBerry]

Check Engine Light On Truck, No Temp Gauge, Set Code

What Is It?

 

[formula]

P0128 Coolant Thermostat Malfunction.



http://www.troublecodes.net/OBD2/Pcodes.shtml



Is the thermostat stuck open? Check if the engine is actually heating up to operating temp. Or that code may be indicating that the coolant temp sensor is toast.



If you search around on here you may find a way to test the resistance of the temp sensor to see if it's functioning properly.



Sean

 

[Bob4x4]

it is a rationality code..... The coolant temperature does not rise by a calibrated amount over a calibrated amount of time.



Bob

 

[Bling-N-Smoke]

If something is indeed wrong... would it be covered under the 100K mile warranty?

 

[Lektrikman]

How do I check MIL codes??

What is the procedure for displaying the MIL code? Will a standard OBD II scanner reveal anything? I've got a check engine light on my 2005 CTD. It is low on fuel but I can't believe that would do it!! Also I've been looking around under the truck and have found the two 1/4" vents on top of the fuel tank. Am considering either plugging them (to keep dirt and polywogs out) or joining them together and taking the vent hose up near the filler neck. ANybody got any ideas??... . Thanks, Lektrikman

 

[JCBerry]

Checking codes

Cycle key on and off 3 times quickly and watch odometer it will display any codes then says done when complete. If you fill your tank with truck running it will sometimes set a code

 

[Bob4x4]

What is the procedure for displaying the MIL code? Will a standard OBD II scanner reveal anything? I've got a check engine light on my 2005 CTD. It is low on fuel but I can't believe that would do it!! Also I've been looking around under the truck and have found the two 1/4" vents on top of the fuel tank. Am considering either plugging them (to keep dirt and polywogs out) or joining them together and taking the vent hose up near the filler neck. ANybody got any ideas??... . Thanks, Lektrikman

DO NOT plug vents adding a short piece of hose is plenty.

 

[Bob4x4]

Cycle key on and off 3 times quickly and watch odometer it will display any codes then says done when complete. If you fill your tank with truck running it will sometimes set a code

Our diesels do not have a leak detection pump... ... ... yet. A loose gas cap will have no effect nor should filling while running.



Bob

 

[Lektrikman]

Bob,

Tell me why to NOT plug the vents... ... I have checked and the fuel cap does vent when subjected to a negative pressure. Any idea why DC would leave these vents open for crap to get into the tank through? I have considered joining the vents to a tee and taking a length of hose up near the filler neck, behind the fender and inserting a vent plug like the ones we have on the differentials. What are your thoughts. Thanks Lektrikman

 

[Bob4x4]

Bob,

Tell me why to NOT plug the vents... ... I have checked and the fuel cap does vent when subjected to a negative pressure. Any idea why DC would leave these vents open for crap to get into the tank through? I have considered joining the vents to a tee and taking a length of hose up near the filler neck, behind the fender and inserting a vent plug like the ones we have on the differentials. What are your thoughts. Thanks Lektrikman

You dont want to create a vacuum in the tank,the pump has to work hard enough with the small diameter lines.



Bob