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Test Description

WARNING: This page is about a different car, the 2004 Chevrolet Corvette. 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. 2:  This step will determine if one or more blower speeds are inoperative.
  2. 4:  This step determines if the HVAC control module and blower motor control processor are attempting to control the blower motor speed.
  3. 6:  The measured voltage on the blower speed control circuit should steadily decrease from 4.60 V to 1.1 V as the blower speed is adjusted from the minimum speed position to the maximum speed position.
Blower Motor Malfunction

Step Action Values Yes No
Schematic Reference: HVAC Schematics 
Connector End View Reference:  HVAC Connector End Views  
DEFINITION: The blower motor operates in at least one, but not all, speed positions.
1 Did you perform the HVAC Diagnostic System Check? - Go to Step 2  Go to Diagnostic System Check - HVAC Systems - Automatic 
2 
  1. Turn ON the ignition, with the engine OFF.
  2. Place the blower motor switch in each speed position.
Does the blower motor operate at the desired speed in each speed position?		 - Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems Go to Step 3 
3
  1. With a scan tool, observe the Desired Blower Mtr Speed parameter in the Heating and Air Conditioning data list.
  2. Gradually adjust the blower motor switch from the minimum speed position to the maximum speed position.
Does scan tool indicate that the Desired Blower Mtr Speed parameter continuously increases within the specified range?		 15-111 counts Go to Step 4  Go to Step 10 
4 
  1. Turn the ignition OFF.
  2. Disconnect the blower motor connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the blower motor supply voltage circuit and the blower motor control circuit.
  5. Adjust the blower motor switch from the minimum speed position to the maximum speed position.
Does the test lamp illuminate and increase intensity?		 - Go to Step 8  Go to Step 5 
5 Test the battery positive voltage circuit and ground circuit of the blower motor control processor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 14  Go to Step 6 
6 
IMPORTANT: The blower motor control processor and HVAC control module connectors must be connected to correctly perform the test.
  1. Backprobe and measure the voltage from the blower speed control circuit at the HVAC control module to a good ground.
  2. Gradually adjust the blower motor switch from the minimum speed position to the maximum speed position.
Does the measured voltage continuously decrease between the specified values?		 4.7-1.0 V Go to Step 9  Go to Step 7 
7
  1. Turn the ignition OFF.
  2. Disconnect the HVAC control module.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the blower speed control circuit of the HVAC control module to a good ground.
Does the voltage measure near the specified value?		 5.0 V Go to Step 10  Go to Step 9 
8 Inspect for poor connections at the harness connector of the blower motor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 14  Go to Step 11 
9 Inspect for poor connections at the harness connector of the blower motor control processor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 14  Go to Step 12 
10 Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 14  Go to Step 13 
11 Replace the blower motor. Refer to Blower Motor Replacement in Heating, Ventilation and Air Conditioning.
Did you complete the replacement?		 - Go to Step 14  -
12 Replace the blower motor control processor. Refer to Blower Motor Control Processor Replacement .
Did you complete the replacement?		 - Go to Step 14  -
13
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 14  -
14 Operate the system in order to verify the repair.
Did you correct the condition?		 - System OK Go to Step 2 
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