GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 Blower Motor Malfunction

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.

  2. This step verifies if the HVAC control switch is attempting to control the blower motor speed.

    3.

  3. This step tests for a voltage change in the blower motor control circuit.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

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

1

Did you review the HVAC operation and perform the necessary inspections?

--

Go to Step 2

Go to Symptoms - HVAC Systems - Automatic

2

  1. Turn ON the ignition, with the engine OFF.
  2. Place the HVAC control module blower switch in each speed position.

Does the blower motor operate in each speed position?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Important: Place the MODE selector in any position except AUTO. Failure to do this may result in a misdiagnosis.

  1. Place the MODE selector in the FLOOR position.
  2. Observe the blower motor PWM parameter.
  3. Rotate the HVAC control module blower switch from the min. to max. speed positions.

Does the blower motor PWM parameter increase within the specified range?

0-98%

Go to Step 4

Go to Step 7

4

  1. Disconnect the blower motor connector.
  2. Connect a test lamp between the blower motor supply circuit and ground circuit.
  3. Rotate the fan control switch from the min. to max. speed position.

Does the test lamp illuminate and change intensity?

--

Go to Step 11

Go to Step 5

5

  1. Backprobe the blower motor control module connector.
  2. Connect a volt meter between the blower motor control circuit and ground circuit.
  3. Rotate the fan control switch from the min. to max. speed position.

Does the voltage vary between the specified value?

0.4-4.0 V

Go to Step 8

Go to Step 6

6

Test the blower motor control circuit for high resistance.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

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 12

Go to Step 9

8

Inspect for poor connections at the harness connector of the blower motor 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 12

Go to Step 10

9

Replace the HVAC control module. Refer to HVAC Control Module Replacement in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

--

Go to Step 12

--

10

Replace the blower motor control module. Refer to Blower Motor Control Processor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the blower motor. Refer to Blower Motor Replacement in Heating, Ventilation and Air Conditioning.

did you complete the replacement?

--

Go to Step 12

--

12

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2