GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Was the heater-A/C Diagnostic System Check performed?

--

Go to Step 2

Refer to Diagnostic System Check

2

Inspect the RADIO-HVAC fuse.

Is the RADIO-HVAC fuse open?

--

Go to Step 3

Go to Step 4

3

Locate and repair a short to ground in circuit 640 (ORN).

Is the repair complete?

--

Go to Step 29

--

4

Inspect the HVAC fuse.

Is the HVAC fuse open?

--

Go to Step 5

Go to Step 6

5

Locate and repair a short to ground in circuit 41 (BRN).

Is the repair complete?

--

Go to Step 29

--

6

Inspect the HIGH BLOWER fuse.

Is the HIGH BLOWER fuse open?

--

Go to Step 7

Go to Step 8

7

Locate and repair a short to ground in circuit 40 (ORN).

Is the repair complete?

--

Go to Step 29

--

8

Verify that ground G200 is clean and tight.

Is ground G200 clean and tight?

--

Go to Step 10

Go to Step 9

9

Clean and tighten G200.

Is the repair complete?

--

Go to Step 29

--

10

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the blower motor electrical connector.
  3. Turn the ignition switch to the ON position.
  4. Press the front defrost button.
  5. Set the blower speed to maximum speed.
  6. Use a test lamp in order to backprobe the blower motor harness connector between terminal A and terminal B.

Does the test lamp light?

--

Go to Step 11

Go to Step 12

11

Replace the blower motor. Refer to Blower Motor and Fan Replacement .

Is the repair complete?

--

Go to Step 29

--

12

  1. Disconnect the blower motor control module connector C1.
  2. Press the front defrost button to the ON position.
  3. Use a Digital Multimeter (DMM) in order to backprobe between the blower motor control module harness connector C1 terminal C and ground.
  4. Measure the voltage while using the blower speed switch to go from minimum to maximum speed.

Does the voltage vary between the specified values?

0.5-7 V

Go to Step 13

Go to Step 18

13

Use a test lamp in order to backprobe between the blower motor control module harness connector C1 terminal A and terminal B.

Does the test lamp light?

--

Go to Step 14

Go to Step 15

14

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

Is the repair complete?

--

Go to Step 29

--

15

Use a test lamp in order to backprobe between the blower motor control module harness connector C1 terminal B and ground.

Does the test lamp light?

--

Go to Step 16

Go to Step 17

16

Locate and repair a poor connection or an open in circuit 150 (BLK) between the blower motor control module harness connector C1 terminal A and G200.

Is the repair complete?

--

Go to Step 29

--

17

Locate and repair a poor connection or an open in circuit 40 (ORN).

Is the repair complete?

--

Go to Step 29

--

18

  1. Disconnect the heater-A/C control.
  2. Use a test lamp in order to backprobe between the heater-A/C control harness connector terminals C1 and C12.

Does the test lamp light?

--

Go to Step 19

Go to Step 21

19

  1. Turn the ignition switch to the ON position.
  2. Use a test lamp in order to backprobe between the heater-A/C control harness connector terminal C1 and terminal C5.

Does the test lamp light?

--

Go to Step 24

Go to Step 20

20

Locate and repair a poor connection or an open in circuit 41 (ORN).

Is the repair complete?

--

Go to Step 29

--

21

Use a test lamp in order to backprobe between the heater-A/C control harness connector terminal C12 and ground.

Does the test lamp light?

--

Go to Step 22

Go to Step 23

22

Locate and repair a poor connection or an open in circuit 1450 (BLK).

Is the repair complete?

--

Go to Step 29

--

23

Locate and repair a poor connection or an open in circuit 640 (ORN).

Is the repair complete?

--

Go to Step 29

--

24

  1. Turn the ignition switch to the OFF position.
  2. Test for continuity of circuit 754 (GRY/BLK) between the heater-A/C control harness connector terminal C11 and the blower motor control module harness connector C1 terminal C.

Is there continuity in the circuit ?

--

Go to Step 26

Go to Step 25

25

Locate and repair a poor connection or an open in circuit 754 (GRY/BLK).

Is the repair complete?

--

Go to Step 29

--

26

  1. Turn the ignition switch to the ON position.
  2. Use a test lamp connected to ground in order to test for a short to B+ on circuit 754 (GRY/BLK).

Is there a short to B+ on the circuit ?

--

Go to Step 27

Go to Step 28

27

Locate and repair the short to B+ on circuit 754 (GRY/BLK).

Is the repair complete?

--

Go to Step 29

--

28

Replace the heater-A/C control. Refer to Control Assembly Replacement .

Is the repair complete?

--

Go to Step 29

--

29

Verify that the system operates properly.

Does the system operate properly?

--

System OK

Go to Symptoms