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Good evening guys (and gals)! I just finally bought my first diesel truck. True to my luck, I’ve had it less than a week and I’m already having problems. I’m really hoping I can get some great knowledge out of you all to ensure this truck lasts me for very many years to come. Now, let’s talk about my new project.... that wasn’t supposed to be a project. She’s a 2007 LBZ, EGR deleted and a single tow tune that adds around 70 hp. Allison tranny. Crew cab with a flatbed. When I got her, the only diagnostic code was P0673. On the way home (towing approx 5K lbs), we started having minor problems. (I’ll post this in somewhere more appropriate, as well.) I noticed her running a little cool. I dismissed it, and I still somewhat do because I figure it’s thermostat stuck open, no big deal. (To me, correct me if I’m wrong) I drove her a couple days to work and back to get a new windshield, tag, title etc. then the real fun started. I’ve now got P0128 Coolant temp low, P003A turbocharger boost control ‘a’ learning limit exceeded, P2563 turbocharger boost control sensor circuit range/performance. A few nights ago, I cranked it (60 degrees outside, no issue) and it was immediately not exactly right. I have very little power, engine sounds fine to me, but may not to someone with more experience. Seems to shift nice and smooth, but it’s hard to know with so little power. The dash lights were also fading in and out, like a failing alternator can cause. The previous owner did tell me that with the tune it will still throw turbo codes sometimes. There was no reduced power mode message on the cluster. I haven’t driven it since. Please help me, if you can. I’ll provide as much info as I can. I’m terrified that it might be a serious problem right after buying it.
 

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Welcome to the DF!
 

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Welcome aboard.
 

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DTC P0128

Diagnostic Instructions



DTC Descriptor

DTC P0128


  • Engine Coolant Temperature (ECT) Below Thermostat Temperature
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 10°C (50°F), low region.
  • The IAT 1 is warmer than 10°C (50°F), high region.
  • The start-up engine coolant temperature is colder than 51°C (124°F).
  • 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 50°C (120°F) low region or 72°C (162°F) 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 +80°C (+19 to +176°F), 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 15°C (27°F) 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. See: Engine, Cooling and Exhaust\Cooling System\Testing and Inspection\Component Tests and General Diagnostics
  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 -39°C (-40°F).
    • 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 149°C (300°F).
    • 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.
 

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Low voltage can cause all sorts of odd electrical issues

What is yoru voltage with the truck is running? Should be 14 +-.

If that is good have both batteries load tested (separately) If one is bad, replace both.

Find out from the previous owner who did the tune? If it is causing turbo issues it needs to be tweaked or replaced.

This thread does not address your current issue but you may bind it worthwhile.

https://www.duramaxforum.com/forum/maintenance/988217-maintenance-info-suggestions-new-owners.html
 
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