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Duramax Third Generation: 2006-2007.5 (LBZ & LLY) Discuss the third generation (2006-2007.5 LBZ & LLY) of the 6.6L Duramax diesel engine & associated components. 2006 LLY engine discussion also belongs in this forum due to the similarities of the 2006 LBZ and the 2006 LLY. Engine related discussion ONLY.


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Old 11-04-2015, 08:54 AM   #1 (permalink)
tjg
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P0128

I'm at my wits end with this truck. It seems as of lately, all I'm getting are codes popping up instead of being able to enjoy the truck.

Last week I got a P0128. Cleared it and then it came back a few days later. Cleared it and it came back last night. I know there is a problem that will be fixed, but I don't want to leave the check engine light on in case if something else goes wrong and it masks the other problem.

Anyways, what is the final fix for this code?

Is it just to change the thermostats? If it is, then I'll try and do it this weekend. I wanted to do a full coolant flush and replace the old coolant with new fresh coolant while changing the thermostats ... but I'm not sure how much that'll cost.

Any help will be appreciated.

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Old 11-04-2015, 09:55 AM   #2 (permalink)
testdrive
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Does the engine warm up to normal temp according to the temp gauge? If you have a non contact thermometer, measure the temp of the pipe at the thermostats.
Possibility of bad thermostat.

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Old 11-04-2015, 10:08 AM   #3 (permalink)
tjg
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Originally Posted by testdrive View Post
Does the engine warm up to normal temp according to the temp gauge? If you have a non contact thermometer, measure the temp of the pipe at the thermostats.
Possibility of bad thermostat.
The engine does warm up to normal temp according to the temp gauge. Approximately 185*.
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Old 11-04-2015, 10:23 AM   #4 (permalink)
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Won't hurt anything to do the thermostats and fluid change first, see if that fixes it. No loss if you were going to anyhow.
Also, any way to measure temp besides guage (ir)? Guage is only glorified idiot light. Does heater blow hot air when "up to temp?"
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Old 11-04-2015, 11:00 AM   #5 (permalink)
tjg
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Originally Posted by TiredFarmer View Post
Won't hurt anything to do the thermostats and fluid change first, see if that fixes it. No loss if you were going to anyhow.
Also, any way to measure temp besides guage (ir)? Guage is only glorified idiot light. Does heater blow hot air when "up to temp?"
Heater works just fine.
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Old 11-04-2015, 03:21 PM   #6 (permalink)
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Circuit/System Description


The engine control module (ECM) uses this diagnostic to determine if the engine coolant temperature (ECT) has reached the minimum calibrated thermostat regulating temperature. The ECM supplies 5 volts to the ECT signal circuit, and a ground for the ECT low reference circuit. The ECM monitors the temperature of the coolant by using the input received from the ECT sensor. The ECM calculates the amount of fuel burned since start-up to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally, or does not reach the regulating temperature of the thermostat, the engine is considered not warm enough for stable, low emission operation.

The purpose of this rationality diagnostics is to use the ECT sensor to determine if the engine coolant will heat up at the correct rate, and also meet the calibrated target temperatures under various operating conditions.

The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation.

Conditions for Running the DTC

  • DTC P0112, P0113, P0116, P0117, P0118 are not set.
  • The engine is running.
  • The IAT 1 is colder than 10C (50F), low region.
  • The IAT 1 is warmer than 10C (50F), high region.
  • The start-up engine coolant temperature is colder than 51C (124F).
  • DTC P0128 will only run once per ignition cycle until a Pass, Fail or Disable condition exists.
Conditions for Setting the DTC

The engine did not meet the ECT target temperatures of 50C (120F) low region or 72C (162F) high region during expected calibrated warm-up times and start-up temperatures.

Action Taken When the DTC Sets

DTC P0128 is a Type B DTC.

Conditions for Clearing the DTC

DTC P0128 is a Type B DTC.

Diagnostic Aids


  • DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation.
  • Inspect the ECT sensor terminals and the ECT harness connector for corrosion. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.
  • This diagnostic runs in a specific range. Measure and record the resistance of the ECT sensor at various ambient temperatures between -7 to +80C (+19 to +176F), then compare those measurements to the Temperature Versus Resistance (EGR Temperature Sensors) Temperature Versus Resistance (ECT Sensors) Temperature Versus Resistance (Fuel Temperature Sensor) Temperature Versus Resistance (IAT Sensor 1) Temperature Versus Resistance (IAT Sensor 2) Temperature Versus Resistance (EGT Sensors) table.
  • A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.
Circuit/System Verification


  1. Ignition OFF, inspect the cooling system surge tank for the proper coolant level.
  2. Ignition OFF for 8 hours or greater.
  3. Ignition ON, observe the scan tool IAT Sensor and ECT Sensor parameters. The ECT, IAT, and ambient temperatures should be within 15C (27F) of each other.
  4. Verify the proper operation of the engine cooling system fan.
Important: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.


  1. Verify the proper heat range and the operation of the thermostat. Refer to Thermostat Diagnosis.
  2. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing


  1. Ignition OFF, disconnect the harness connector at the ECT sensor.
  2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal A and ground.
    • If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  1. Ignition ON, verify the scan tool ECT parameter is colder than -39C (-40F).
    • If greater than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.
  1. Install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool ECT parameter is warmer than 149C (300F).
    • If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  1. If all circuits test normal, test or replace the ECT sensor.
Component Testing


  • Measure and record the resistance of the ECT sensor at various ambient temperatures and compare those measurements to the Temperature vs. Resistance table.
  • Refer to Thermostat Diagnosis.
Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


  • Engine Coolant Thermostat Replacement
  • Engine Coolant Temperature Sensor Replacement
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Old 11-04-2015, 06:18 PM   #7 (permalink)
Ramblinrodney
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There are YouTube vidio's how to change.
DIY https://www.dieselplace.com/forum/71-...placement.html
There are also a lot of helpful hints on here. Just search.
DTC P0128 is designed to detect for a stuck open thermostat

Document ID# 1625680
2006 GMC Truck GMC K Sierra - 4WD DTC P0128

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss1-1625680">Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss2-1625680">DTC Descriptor

DTC P0128: Engine Coolant Temperature (ECT) Below Thermostat Temperature

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss3-1625680">Diagnostic Fault Information

Circuit
Short to Ground
Open/High Resistance
Short to Voltage
Signal Performance
ECT Sensor Signal
P0117
P0118
P0118
P0116, P0128
Low Reference
P0118
P0118
P0128
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss4-1625680">Typical Scan Tool Data

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#tab5-1625680">ECT Sensor Temperature

Circuit
Normal Range
Short to Ground
Open
Short to Voltage
Operating Conditions: Key ON, engine OFF
ECT Sensor Signal
Varies
150C (302F)
-40C (-40F)
-40C (-40F)
Low Reference
--
--
-40C (-40F)
-40C (-40F)
Varies -39 to +149C (-38 to +300F)
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss6-1625680">Circuit/System Description

The engine control module (ECM) uses this diagnostic to determine if the engine coolant temperature (ECT) has reached the minimum calibrated thermostat regulating temperature. The ECM supplies 5 volts to the ECT signal circuit , and a ground for the ECT low reference circuit. The ECM monitors the temperature of the coolant by using the input received from the ECT sensor. The ECM calculates the amount of fuel burned since start-up to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally, or does not reach the regulating temperature of the thermostat, the engine is considered not warm enough for stable, low emission operation.
The purpose of both these rationality diagnostics is to use the ECT sensor to determine if the engine coolant will heat up at the correct rate, and also meet the calibrated target temperatures under various operating conditions.
The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss7-1625680">Conditions for Running the DTC

• DTC P0112, P0113, P0116, P0117, P0118 are not set.
• The engine is running.
• The IAT 1 is greater than -7C (19F), but less than 100C (212F).
• The start-up engine coolant temperature is less than 65C (149F).
• DTC P0128 will only run once per ignition cycle until a Pass, Fail or Disable condition exists.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss8-1625680">Conditions for Setting the DTC

The engine did not meet the ECT target temperature of 45C (113F) or 72C (162F) during expected calibrated warm-up times and start-up temperatures.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss9-1625680">Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss10-1625680">Conditions for Clearing the DTC

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and the DTC with a scan tool.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss11-1625680">Diagnostic Aids

DTC P0128 is designed to detect for a stuck open thermostat.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1625680&psdid=1233&evc=sm#ss12-1625680">Reference Information
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Last edited by Ramblinrodney; 11-04-2015 at 06:30 PM.
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Old 11-04-2015, 10:43 PM   #8 (permalink)
tjg
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CEL light came back on on the way home from work.

I'm going to try and change the thermostats myself this weekend because it's starting to piss me off lol.

Now, I've never done this before. Is there a step by step how-to to do this? How difficult is it to do?

I'd rather do it myself rather than pay someone.
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Old 11-05-2015, 09:15 AM   #9 (permalink)
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Quote:
Originally Posted by tjg View Post
Now, I've never done this before. Is there a step by step how-to to do this? How difficult is it to do?
Didn't you see the link I put up from our DIY? I'll put it up again.
https://www.dieselplace.com/forum/71-...placement.html
Here is how Eric does this.
https://www.youtube.com/watch?v=qjXDifpGGrs
More
https://www.youtube.com/watch?v=75oAX-w-JGE
More
Coolant change from our DIY. Lots of YouTube vidios on this.
https://www.dieselplace.com/forum/71-...ks-arcing.html
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Transgo Jr. PCV Reroute kit, Trans Line Repair Kit By Dirty Hooker Diesel,
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Last edited by Ramblinrodney; 11-05-2015 at 09:27 AM.
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Old 11-05-2015, 10:04 AM   #10 (permalink)
testdrive
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Good work Rodney and Ron, can't be more clear.

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