GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 Auxiliary Blower Motor Inoperative

Auxiliary Blower Motor Inoperative W/O Sunroof

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This step tests for auxiliary blower motor operation in any speed setting.

    2.

  2. This step identifies if the auxiliary HVAC control module is commanding the auxiliary blower motor to operate at HI speed.

    3.

  3. This step verifies that power is being supplied to the auxiliary blower motor.

    4.

  4. This step tests for a possible open in the auxiliary blower motor ground circuit or a poor motor.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

DEFINITION: The auxiliary blower motor is inoperative in all speed positions.

1

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

--

Go to Step 2

Go to Symptoms - HVAC Systems - Automatic

2

Important: The rear auxiliary HVAC control switch will only function if the front auxiliary HVAC control switch is placed in the REAR position.

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

Are both auxiliary control modules inop in all speeds?

--

Go to Step 5

Go to Step 3

3

Does only the front auxiliary control module operate?

--

Go to Step 11

Go to Step 4

4

Does only the rear auxiliary control module operate?

--

Go to Step 15

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

5

Important: Place the front auxiliary HVAC control switch in the REAR position. Place the rear auxiliary HVAC control switch in the HI speed position. Place the MODE selector in any position except AUTO. This will ensure a full speed condition when the auxiliary blower motor is commanded to an ON position. Failure to do this may result in a misdiagnosis.

  1. Place the rear auxiliary HVAC control module blower switch in the max. speed position.
  2. Place the MODE selector in the FLOOR position.
  3. Command the auxiliary blower motor to the ON state.
  4. Observe the auxiliary blower motor PWM parameter.

Is the auxiliary blower motor PWM parameter at the specified value?

98%

Go to Step 6

Go to Step 17

6

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

Does the test lamp illuminate and change intensity?

--

Go to Step 7

Go to Step 9

7

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

Does the test lamp illuminate and change intensity?

--

Go to Step 19

Go to Step 8

8

Test the rear blower motor control module ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 14

9

Test the rear blower motor control module battery positive voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 10

10

Test the rear Heater and A/C blower motor control module control circuit for a high resistance, open or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 12

11

Test the blower speed control circuit between the front and rear auxiliary HVAC control modules.

Did you find and correct the condition?

--

Go to Step 20

--

12
  1. With a volt meter backprobe the auxiliary blower motor control circuit at the auxiliary blower motor control module.
  2. Rotate the fan control switch from the LOW to HI speed position.

Does the voltage vary between the specified value?

0.4-4.0 V

Go to Step 16

Go to Step 13

13

Inspect for poor connections at the harness connector of the rear 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 20

Go to Step 15

14

Inspect for poor connections at the harness connector of the auxiliary 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 20

Go to Step 18

15

Inspect for poor connections at the harness connector of the front 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 20

Go to Step 16

16

Replace the front HVAC control module. Refer to Auxiliary Heater and Air Conditioning Control Replacement - Front in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

--

Go to Step 20

--

17

Replace the rear HVAC control module. Refer to Auxiliary Heater and Air Conditioning Control Replacement - Front in Heating, Ventilation and Air Conditioning.

Did you complete the replacement?

--

Go to Step 20

--

18

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

Did you complete the replacement?

--

Go to Step 20

--

19

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

Did you complete the replacement?

--

Go to Step 20

--

20

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2