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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1857 (Engine Controls And Fuel - 3.5L (L66) - DTC P0030 To DTC P0222) >> DTC P0128 >> Test Description

Test Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 1:  The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
  2. 2:  This step compares the ECT temperature to the IAT temperature. This inspection is to be performed when the vehicle has reached ambient room temperature. At that time both the surrounding air temperature and the engine coolant temperature are nearly equal. If the ECT sensor and circuit are OK, both sensors should indicate the same temperature.
  3. 3:  This step checks that the temperature of the engine coolant increases at least 60°C (140°F) within 20 minutes. If the temperature does not increase to the specified value there is a fault with the ECT sensor or the engine cooling system.
  4. 4:  This step checks for a correctly operating engine cooling fan. A cooling fan that comes ON too soon or stays ON all the time, can cause a DTC P0128 to set.
  5. 5:  Fault not present indicates the condition that caused DTC P0128 to set is intermittent and not currently present. If no other DTCs are stored, refer to Diagnostic Aids for additional information on diagnosing an intermittent DTC P0128.
  6. 16:  After replacing the PCM the relationship between the CKP sensor and the crankshaft must re-established. A new minimum throttle position and idle speed must also be established.
DTC P0128

Step Action Values Yes No
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1  Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
  1. Allow the engine to cool to the ambient air temperature.
  2. Turn ON the ignition, with the engine OFF.
  3. Compare the engine coolant temperature (ECT) sensor temperature reading to the intake air temperature (IAT) sensor temperature reading on a scan tool.
Are the ECT and the IAT readings within 2 or 3 degrees of each other?		 - Go to Step 3  Go to Step 6 
3 
  1. Start the engine and immediately observe the ECT on the scan tool.
  2. Continue to observe the ECT while idling the engine for 10 minutes.
Does the ECT indicated on the scan tool increase to at least the specified value within the 20 minutes?		 60°C (140°F) Go to Step 5  Go to Step 4 
4  Test for the correct operation of the engine cooling fan. Refer to Cooling Fan Always On (3.5L) .
Did you find and repair a condition with engine cooling fan operation?		 - Go to Step 17  Go to Step 6 
5  The fault is not present.
Are there any DTCs stored that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Diagnostic Aids In This Test
6
  1. Disconnect the ECT sensor electrical connector.
  2. Measure the resistance of the ECT sensor with a DMM.
  3. Compare the measured resistance of the ECT sensor with the resistance values in the Temperature vs Resistance table. Refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor .
Is the resistance of the ECT sensor within specifications?		 - Go to Step 7  Go to Step 14 
7
  1. Disconnect the ECT sensor electrical connector.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the ECT sensor temperature with a scan tool.
Does the scan tool indicate that the ECT sensor temperature is at the specified value?		 -40°C (-40°F) Go to Step 8  Go to Step 12 
8
  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the signal circuit and the sensor ground circuit of the ECT sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the ECT sensor temperature with a scan tool.
Does the scan tool indicate that the ECT sensor temperature is at the specified value?		 215°C (419°F) Go to Step 13  Go to Step 9 
9
  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the signal circuit and a known good ground.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the ECT sensor temperature with a scan tool.
Does the scan tool indicate that the ECT sensor temperature is at the specified value?		 215°C (419°F) Go to Step 10  Go to Step 11 
10
  1. Test the ECT sensor ground circuit for high resistance. Refer to Circuit Testing .
  2. Repair as necessary. Refer to Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 17  Go to Step 15 
11
  1. Test the ECT sensor signal circuit for high resistance. Refer to Circuit Testing .
  2. Repair as necessary. Refer to Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 17  Go to Step 15 
12
  1. Test the ECT sensor signal circuit for a short to ground.
  2. Repair as necessary. Refer to Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 17  Go to Step 15 
13
  1. Inspect the engine cooling system for all of the following:
  2. Repair as necessary.
Did you complete the action?		 - Go to Step 17  -
14 Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .
Did you complete the replacement?		 - Go to Step 17  -
15
  1. Inspect the powertrain control module (PCM) and the ECT sensor electrical connectors for poor connections. Refer to Testing for Intermittent Conditions and Poor Connections .
  2. Repair as necessary. Refer to Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 17  Go to Step 16 
16 
  1. Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
  2. Perform the idle learn procedure. Refer to Idle Learn .
Did you complete the replacement?		 - Go to Step 17  -
17
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 18 
18 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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