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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 965 (Engine Controls Diagnosis - 6.6L (Lb7) (DTCS P0016 To P0236)) >> Diagnosis >> DTC P0128 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. 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. 3:  This step tests for excessive resistance in the ECT circuit.
  2. 7:  This step tests for a skewed sensor through the range of temperatures affecting this DTC.
DTC P0128

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Control Module (ECM) Connector End Views  or  Engine Controls Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 Is the cooling system coolant low? - Go to Loss of Coolant in Engine Cooling Go to Step 3 
3 
  1. Disconnect the engine coolant temperature (ECT) sensor.
  2. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and the low reference circuit of the ECT sensor.
  3. Observe the ECT sensor parameter with a scan tool.
Is the ECT sensor parameter more than the specified value?		 146° C (294° F) Go to Step 7  Go to Step 4 
4
  1. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a good ground.
  2. Observe the ECT sensor parameter with a scan tool.
Is the ECT sensor parameter more than the specified value?		 146° C (294° F) Go to Step 5  Go to Step 6 
5 Test the ECT sensor low reference circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 10  Go to Diagnostic Aids
6 Test the ECT sensor signal circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 10  Go to Diagnostic Aids
7 
  1. Remove the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
  2. Suspend the ECT sensor and a thermometer in a pan of water.
  3. Place the pan on a burner or hot plate.
  4. Test the resistance of the ECT sensor through the specified range of temperatures. Refer to Temperature vs Resistance .
Does the resistance and temperature closely match the Temperature vs Resistance Table?		 10° -90° C (50° -194° F) Go to Step 8  Go to Step 9 
8 Install the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
Did you complete the action?		 - Go to Engine Fails To Reach Normal Operating Temperature in Engine Cooling -
9 Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
Did you complete the replacement?		 - Go to Step 10  -
10
  1. Clear the DTC's 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 11 
11 Observe the Capture Info with a scan tool.
Are there any DTC's that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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