Engine code P0128 - Chevy and GMC Duramax Diesel Forum
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Old 02-04-2010, 06:26 PM   eBay Motors  #1 (permalink)
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Engine code P0128

Anyone know why im getting engine coolant below thermostat regulating temp? This only happens when I'm babying the truck if I play somewhat with the throttle the code dosen't show.
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Old 02-04-2010, 06:51 PM   eBay Motors  #2 (permalink)
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So what coolant temps are you seeing on the gage when you get this code?
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Old 02-04-2010, 07:18 PM   eBay Motors  #3 (permalink)
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The ECM is calculating an expected Coolant Temp given the fuel that has been burned and the time that it has been burning it. If the coolant temp does not meet or exceed the calculated temp, you get the code.

Check for proper coolant level.

Perform Coolant System Leak Test.

Inspect fan for proper operation.

Inspect the fan belt to ensure it is in good operating condition?

Remove thermostats and verify proper operation. Bring to boil in a pot of water and see what temps they open and close at. Start opening ~ 160 Fully open at ~ 180 Degrees F roughly.

Could also be a bad ECT Sensor. You can do a resistance check at various temps. At 0 degrees F Res = 9420 ohms At 50 degrees F Res = 973 ohms at 100 degrees F Res = 177 ohms, at 150 degrees F Res = 47 ohms.

This condition could also be caused by air in the coolant system. That could possibly be an indicator of a bad head gasket. After shutting the warmed engine off, and letting it set for several hours, check the upper Rad hose to see if it is hard. If it is hard, you probably should test for a headgasket failure.

Did you try running it at a different tune to see if you still get the code? If all the above is within Spec, then the tuner could be causing the ECM to give you a bad calculation.
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Last edited by Len Todd; 02-04-2010 at 07:21 PM.
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Old 02-04-2010, 08:03 PM   eBay Motors  #4 (permalink)
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Thanks Ill check all that implies tomorrow.
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Old 02-04-2010, 08:05 PM   eBay Motors  #5 (permalink)
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And since the engine build the truck runs very cool maybe 150 -180
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Old 02-04-2010, 08:10 PM   eBay Motors  #6 (permalink)
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That was a good response from Len Todd--

Diesels like a certain temperature to run well and be efficent-- it is possible that someone replaced the thermostats with cooler ones. Most have a stamp on that shows the set temperature.
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Old 02-05-2010, 07:24 PM   eBay Motors  #7 (permalink)
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where was this answer for me 2 month ago lol. I started getting this code after I had bigger nozzles put on my injectors when the cooler temperatures hit here. I Was able to adjust the tuning to almost eliminate the code. still pops up every once in a while usually after its partially warmed up and I jump on it to get into traffic or something
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