For 1990-2009 cars
HVAC Components
HVAC Air Delivery/Temperature Control Schematics Buick
HVAC Air Delivery/Temperature Control Schematics Buick, Oldsmobile
Handling ESD Sensitive Parts Notice
Data Link Connector Schematics
HVAC Air Delivery/Temperature Control Schematics Buick
HVAC Air Delivery/Temperature Control Schematics Buick, Oldsmobile

### Circuit Description

The ambient air temperature sensor is a thermistor that controls signal voltage to the HVAC programmer. The HVAC programmer supplies voltage on CKT 735. When the sensor is cold, the resistance is high and the HVAC programmer will sense a high signal voltage at terminal B1. When the sensor warms, resistance is reduced and the signal voltage is pulled low through CKT 61. Signal voltage will vary from 5 V (open circuit) to 0 V (short circuit).

### Conditions for Setting the DTC

• | The ignition is ON.

• | Circuit open or shorted.

### Action Taken When the DTC Sets

• | A blank is displayed on the drivers information center.

• | A default value of 15° C (59° F) will be used by the HVAC programmer in order to allow operation of the A/C system.

### Conditions for Clearing the DTC

• | Using a Scan Tool .

• | A history DTC will clear when 50 consecutive ignition cycles have occurred without a malfunction.

• | HVAC programmer battery voltage is interrupted.

### Test Description

1. This step ensures that the DTC was not set in error.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the ambient temperature sensor.
3. Using a J 39200 digital multimeter (DMM) measure the resistance between the sensor terminal A and terminal B. Refer to Testing for Continuity in Wiring Systems.

Refer to Sensor Resistance Table . Is the resistance within the specified range according to the table?

--

Go to Step 3

Go to Step 2

2 | Replace the sensor. Refer to Ambient Temperature Sensor Replacement . Is the repair complete? | -- | System OK | --
3 |

1. Turn the ignition switch to the ON position.
2. Use a J 39200 digital multimeter (DMM) in order to measure the voltage between terminal A and terminal B of the sensor harness connector. Refer to Measuring Voltage in Wiring Systems.

Is the voltage approximately equal to the specified value?

5 V

Go to Step 4

Go to Step 8

4 |

1. Turn the ignition switch to the OFF position.
2. Reconnect the ambient temperature sensor.
3. Turn the ignition switch to the ON position.
4. Clear the DTC using a Scan Tool .
5. Turn the ignition switch to the OFF position.
6. Turn the ignition switch to the ON position.

Does the DTC reset?

--

Go to Step 5

Go to Intermittents and Poor Connections Diagnosis

5 | Inspect all of the related connectors for proper terminal contact. Refer to Intermittents and Poor Connections . Is the terminal contact correct? | -- | Go to Step 6 | Go to Step 7
6 | Replace the HVAC programmer. Refer to Programmer Replacement . Is the repair complete? | -- | System OK | --
7 | Correct the terminal contact. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. Is the repair complete? | -- | System OK | --
8 | Is the voltage greater than the specified value? | 5 V | Go to Step 9 | Go to Step 10
9 | Repair the short to battery in CKT 735. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | System OK | --
10 | Use a J 39200 digital multimeter (DMM) in order to measure the voltage between sensor terminal A and the DLC terminal 4. Refer to Measuring Voltage in Wiring Systems. Is the voltage approximately equal to the specified value? | 5 V | Go to Step 14 | Go to Step 11
11 | Use a J 39200 digital multimeter (DMM) in order to backprobe and measure the voltage between HVAC programmer terminal B1 and the DLC terminal 4. Refer to Probing Electrical Connectors and Measuring Voltage in Wiring Systems. Is the voltage approximately equal to the specified value? | 5 V | Go to Step 12 | Go to Step 13
12 | Repair the open in CKT 735. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | System OK | --
13 | Replace the HVAC programmer. Refer to Programmer Replacement . Did you replace the programmer? | -- | System OK | --
14 | Are all of the sensor DTCs present? | -- | Go to Step 15 | Go to Step 17
15 | Inspect CKT 61 for opens. Is the circuit OK? | -- | Go to Step 16 | Go to Step 17
16 | Replace the HVAC programmer. Refer to Programmer Replacement . Is the repair complete? | -- | System OK | --
17 | Repair the open in CKT 61. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | System OK | --