GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Was a diagnostic system check performed?

--

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Manual

2

Exchange the blower motor relay with a known good relay from the underhood wiring harness junction block.

Does the blower motor operate?

--

Go to Step 3

Go to Step 4

3

Replace the faulty relay.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

4

Backprobe the underhood wiring harness junction block connector C3 using a fused jumper between terminal B9 and B+.

Does the blower motor operate?

--

Go to Step 10

Go to Step 5

5

  1. Turn the ignition switch to the RUN position.
  2. Turn the blower switch to M3.
  3. Disconnect the blower motor connector.
  4. Connect a test lamp between terminal B of the blower motor connector and ground.

Does the test lamp light?

--

Go to Step 6

Go to Step 7

6

Connect a test lamp between terminal A and terminal B of the blower motor connector.

Does the test lamp light?

--

Go to Step 8

Go to Step 9

7

Repair the open in CKT 65 between the underhood wiring harness junction block and the blower motor. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

8

Replace the blower motor.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

9

Repair the open in CKT 250 between the blower motor and ground splice pack G203. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

10

  1. Turn the ignition switch to the RUN position.
  2. Use the J 39200 Digital Multimeter (DMM) in order to backprobe the heater A/C control assembly connector C1.
  3. Measure the voltage between terminal B and ground.

Does the voltage measured equal the specified value?

B+

Go to Step 14

Go to Step 11

11

  1. Use the J 39200 DMM in order to backprobe the right side IP wiring harness junction block connector C1.
  2. Measure the voltage between terminal A5 and ground.

Does the voltage measured equal the specified value?

B+

Go to Step 13

Go to Step 12

12

Repair the open in CKT 641 between the right side IP wiring harness junction block and the heater A/C control assembly. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

13

Replace the right side IP wiring harness junction block. Refer to Underhood Fuse Block Replacement in Engine Electrical.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

14

  1. Turn the blower switch to M3.
  2. Use the J 39200 DMM in order to backprobe the heater A/C control assembly connector C1.
  3. Measure the voltage between terminal E and ground.

Does the voltage measured equal the specified value?

B+

Go to Step 16

Go to Step 15

15

Replace the heater A/C control assembly.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

16

  1. Disconnect the blower resistor assembly connector.
  2. Turn OFF the ignition.
  3. Disconnect the underhood wiring harness junction block connector C3.
  4. Use a J 39200 DMM in order to measure the resistance between the blower resistor connector terminal E and the junction block connector C3 terminal C10.

Is the resistance within the specified range?

0-2ohms

Go to Step 17

Go to Step 19

17

Backprobe the underhood wiring harness junction block connector C3 using a fused jumper between terminal C10 and B+.

Does the blower motor operate?

--

Go to Step 18

Go to Step 20

18

Replace the blower resistor assembly.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

19

Repair the open in CKT 101 between the blower resistor terminal E and the underhood wire harness junction block connector C3 terminal C10. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - HVAC Systems - Manual

--

20

Replace the underhood wiring harness junction block. Refer to Underhood Fuse Block Replacement in Engine Electrical.

Is the repair complete?

--

System Ok

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