For 1990-2009 cars

### 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. This step determines if the HVAC control module and blower motor control processor are attempting to control the blower motor speed.

3. The measured voltage on the blower speed request signal circuit should steadily increase from 3.0 V to 9.0 V as the blower speed is adjusted from the minimum speed position to the maximum speed position.

4. The blower motor speed signal circuit is spliced to the blower motor control circuit.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views DEFINITION: The blower motor operates in at least one, but not all, speed positions.
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - HVAC Systems - Automatic
2 |

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

Does the blower motor operate at the desired speeds?

--

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

Go to Step 3

3 |

1. Turn the ignition OFF.
2. Disconnect the blower motor connector.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the blower motor supply voltage circuit and the blower motor control circuit.
5. Adjust the blower motor switch from the minimum speed position to the maximum speed position.

Does the test lamp illuminate and increase intensity?

--

Go to Step 8

Go to Step 4

4 | Test the battery positive voltage circuit and blower motor control circuit of the blower motor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 5
5 | Important: The blower motor control processor and HVAC control module connectors must be connected to correctly perform the test.

1. Backprobe and measure the voltage from the blower speed request signal circuit at the HVAC control module to a good ground.
2. Gradually adjust the blower motor switch from the minimum speed position to the maximum speed position.

Does the measured voltage continuously increase between the specified values?

3.0-9.0 V

Go to Step 7

Go to Step 6

6 | Test the blower motor speed request signal circuit for an short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10
7 | Test the blower motor speed signal circuit for an short to voltage, 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 14 | Go to Step 9
8 | Inspect for poor connections at the harness connector of the blower motor. 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 14 | Go to Step 11
9 | Inspect for poor connections at the harness connector of the blower motor control processor. 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 14 | Go to Step 12
10 | 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 14 | Go to Step 13
11 | Replace the blower motor. Refer to Blower Motor Replacement in Heating, Ventilation and Air Conditioning. Did you complete the replacement? | -- | Go to Step 14 | --
12 | Replace the blower motor control processor. Refer to Blower Motor Control Processor Replacement . Did you complete the replacement? | -- | Go to Step 14 | --
13 | Important: Perform the recalibration procedure for the HVAC control module. Replace the HVAC control module. Refer to HVAC Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | --
14 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2