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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1712 (HVAC Systems - Automatic) >> Diagnostic Information and Procedures >> DTC B0408 >> Test Description

Test Description

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

  1. 3:  This step determines if the air temperature door position is within the specified range of the commanded value.
  2. 6:  Tests for a short to voltage in the 5-volt reference circuit.
DTC B0408

Step Action Values Yes No
Schematic Reference:  HVAC Schematics  
1 Did you perform the HVAC Diagnostic System Check? - Go to Step 2  Go to Diagnostic System Check - HVAC Systems - Automatic 
2
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, check the DTC.
Does the scan tool indicate that DTC B0248, B0268, B0429 and B03531 set along with B0408?		 - Go to Diagnostic Trouble Code (DTC) List  Go to Step 3 
3 
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, observe the Air Mix Door Commanded data parameter and the Air Mix Door Actual data parameter in the Primary ECC Data list.
Does the scan tool indicate that the Air Mix Door Commanded data parameter is within the specified value of the Air Mix Door Actual data parameter?		 0-3 Counts Go to TESTING FOR INTERMITTENT AND POOR CONNECTIONS Go to Step 4 
4
  1. With the scan tool, command the air temperature actuator from HOT (Off) to COLD (On).
  2. With the scan tool, observe the Air Mix Door Actual parameter in the Primary ECC data list.
Does the Air Mix Door Actual data parameter change at all?		 - Go to Step 9  Go to Step 5 
5 Test the ignition 3 voltage circuit of the air temperature actuator for an open or a high resistance. Refer to CIRCUIT TESTING and WIRING REPAIRS .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 6 
6  Test the 5 volt reference circuit of the air temperature actuator for an open, high resistance, short to ground or short to voltage. Refer to CIRCUIT TESTING and WIRING REPAIRS .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 7 
7 Test the air temperature door control circuit of the air temperature actuator for an open, high resistance, short to ground or short to voltage. Refer to CIRCUIT TESTING and WIRING REPAIRS .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 8 
8 Test the air temperature actuator ground for open or high resistance. Refer to CIRCUIT TESTING and WIRING REPAIRS .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 9 
9
IMPORTANT: The air temperature actuator connector and the HVAC control module connector must be connected to correctly perform test.
  1. Turn ON the ignition, with the engine OFF.
  2. With the scan tool, observe the Air Mix Door Actual data parameter in the Primary ECC Data list.
  3. Connect a 3-amp fused jumper wire between the air temperature door control circuit and the 5-volt reference circuit of the air temperature actuator. This drives the actuator to the full COOL position.
  4. Remove and reconnect the jumper wire between the air temperature door control circuit and the ground circuit of the air temperature actuator. This drives the actuator to the full HOT position.
Does the air temperature actuator drive shaft rotate and do the counts change?		 - Go to Step 12  Go to Step 10 
10 Inspect the air temperature door and the air temperature actuator for the following:
  • Incorrectly installed air temperature actuator.
  • Broken or binding linkages or air temperature door.
  • Obstruction that prevents the air temperature door from operating within it's full range of motion.

Did you find and correct the condition?		 - Go to Step 15  Go to Step 11 
11 Inspect for poor connections at the harness connector of the air temperature actuator. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS and CONNECTOR REPAIRS .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 13 
12 Inspect for poor connections at the harness connector of the HVAC control module. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS and CONNECTOR REPAIRS .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 14 
13
IMPORTANT: Perform the recalibration procedure for the air temperature actuator.
Replace the air temperature actuator. Refer to AIR TEMPERATURE ACTUATORS .Did you complete the replacement?		 - Go to Step 15  -
14
IMPORTANT: Perform the recalibration procedure for the HVAC control module.
Replace the HVAC control module. Refer to HVAC Control Module Replacement .Did you complete the replacement?		 - Go to Step 15  -
15
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?		 - Go to Step 2  System OK
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