1. Install the scan tool.
2. Turn the ignition switch to the RUN position.
3. Ensure that the engine is OFF.
4. Inspect for heater and A/C control diagnostic trouble codes (DTCs).

Do any DTCs exist?

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Go to Step 2

Go to DTC Table

Inspect the heater and A/C control modes.

Are all of the modes inoperative?

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Go to Step 3

Go to Step 21

Turn ON the radio.

Does the radio have power?

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Go to Step 4

Go to Step 10

Inspect the HVAC fuse 1.

Is the fuse open?

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Go to Step 15

Go to Step 5

1. Connect a J 39200 .
2. Backprobe between the heater and A/C control connector terminal C12 to ground.

Is the voltage within the specified range?

9-16 V

Go to Step 6

Go to Step 9

1. Turn the ignition switch ON.
2. Connect a J 39200 .
3. Backprobe between the heater and A/C control connector terminal C6 to ground.

Is the voltage within the specified range?

9-16 V

Go to Step 22

Go to Step 8

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

Is the replacement complete?

--

System OK

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Repair an open in CKT 341.

Is the repair complete?

--

System OK

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Repair an open in CKT 340. Note: This circuit also feeds the instrument cluster and radio.

Is the repair complete?

--

System OK

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Inspect the RDO BATT fuse.

Is the fuse open?

--

Go to Step 11

Go to Step 9

1. Remove the RDO BATT fuse.
2. Connect a J 39200 .

Important: The load side of the fuse is the terminal without battery voltage.

3. Measure the resistance of the load side of the RDO BATT fuse, terminal B to battery ground. Leave the meter connected until the test is complete or until you are told to remove the meter.

Is the reading less than the specified value?

0.5 ohms

Go to Step 12

Go to Step 14

Disconnect the heater and A/C control module connector.

Is the reading less than the specified value?

0.5 ohms

Go to Step 13

Go to Step 7

Repair a short to ground in CKT 340. CKT 340 also feeds the instrument cluster and radio.

Is the repair complete?

--

System OK

--

Replace the RDO BATT fuse.

Is the repair complete?

--

System OK

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1. Remove the HVAC fuse.
2. Connect a J 39200 .
3. Measure the resistance of the load site of the HVAC fuse, terminal B to battery ground.
4. Leave the J 39200 connected until the test is complete or until you are told to remove it. The load side of the fuse is the terminal without the battery voltage with the ignition switch in RUN.

Is the reading less than the specified value?

0.5 ohms

Go to Step 16

Go to Step 18

Disconnect the heater and A/C control module connector.

Is the reading less than specified?

0.5 ohms

Go to Step 17

Go to Step 7

Repair a short to ground in CKT 341.

Is the repair complete?

--

System OK

--

Replace the HVAC fuse.

Is the replacement complete?

--

System OK

--

Request a heating and A/C menu selection on the scan tool.

Are any current DTCs displayed?

--

Go to Step 20

Go to HVAC System Check

1. Turn the ignition switch to the OFF position.
2. Record the displayed DTCs.
3. Diagnose the current DTCs from lowest to highest.
4. Refer to the diagnostic aids for that specific DTC when only a history exists. A history DTC indicates the malfunction has been repaired or is intermittent.
5. Clear all of the current DTCs.

Are all the DTCs cleared?

--

Go to DTC Table

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Inspect the heater and A/C control operation.

Is the scan tool communicating correctly?

--

Go to Scan Tool Does Not Communicate with Heater and Air Conditioning (A/C) Control in Wiring Systems

Go to Step 19

1. Turn the ignition switch to the OFF position.
2. Disconnect the heater and A/C control module.
3. Connect a test lamp between the heater and A/C control harness connector terminals C10 and C12.

Does the test lamp light?

--

Go to Step 7

Go to Step 23

Repair an open in CKT 1050.

Is the repair complete?

--

System OK

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