GM Service Manual Online
For 1990-2009 cars only

Test Description

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

  1. This step will determine if one or more blower speeds are inoperative.

  2. This step determines if the HVAC control module and auxiliary blower motor control processor are attempting to control the auxiliary blower motor speed.

  3. The measured voltage on the auxiliary blower speed control circuit should increase from 0-8 volts as the auxiliary blower speed is adjusted from the minimum speed position to the maximum speed position. The voltage may increase slightly between speeds 1 and 2.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: The auxiliary blower motor operates in at least one, but not all, speed positions.

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn ON the ignition, with the engine OFF.
  2. Place the auxiliary blower motor switch in each speed position.

Does the auxiliary blower motor operate at the desired speeds?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the auxiliary blower motor connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the auxiliary blower motor supply voltage circuit and the auxiliary blower motor control circuit.
  5. Adjust the auxiliary 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 4

4

Test the ground circuit of the blower motor control processor for high resistance or an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 5

5

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 auxiliary blower speed control circuit at the HVAC control module to a good ground.
  2. Adjust the auxiliary blower motor switch from the minimum speed position to the maximum speed position.

Does the measured voltage continuously increase between the specified values?

0-8.0 V

Go to Step 7

Go to Step 6

6

Test the auxiliary blower motor speed control circuit for an short to voltage, open or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 10

7

Test the auxiliary blower motor speed signal circuit for an short to voltage, open or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 9

8

Inspect for poor connections at the harness connector of the auxiliary blower motor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

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 auxiliary blower motor resistor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

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 .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

11

Replace the auxiliary blower motor. Refer to Auxiliary Blower Motor Replacement .

Did you complete the replacement?

--

Go to Step 14

--

12

Replace the auxiliary blower motor resistor. Refer to Auxiliary Blower Motor Resistor Replacement .

Did you complete the replacement?

--

Go to Step 14

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13

Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 14

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14

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2