For 1990-2009 cars
HVAC Components
Cell 68: Heater and A/C Programmer - Oldsmobile
Cell 68: Heater and A/C Programmer - Buick
Cell 68: Heater and A/C Programmer - Pontiac
Handling ESD Sensitive Parts Notice

### Circuit Description

The Ambient Air Temperature Sensor is a thermistor that controls signal voltage to the HVAC programmer. The HVAC programmer supplies voltage on circuit 735. When the sensor is cold, the resistance is high and the HVAC programmer will sense a high signal voltage at terminal F8 (Buick, Oldsmobile) or terminal D8 (Pontiac). When the sensor warms, resistance is reduced and the signal voltage is pulled low through circuit 1704. 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 to allow operation of the A/C system.

### Conditions for Clearing the DTC

• | Using a Scan Tool .

• | A history DTC will clear when 40 consecutive ignition cycles have occurred without a malfunction.

• | HVAC programmer battery voltage is interrupted.

### Test Description

1. Ensures that the DTC was not set in error.

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

1. Turn the ignition to the OFF position.
2. Disconnect the sensor.
3. Measure the resistance between sensor terminal A and terminal B. Refer to Sensor Resistance Table .

Is the resistance within the range specified in the table?

--

Go to Step 2

Go to Step 5

2 |

1. Turn the ignition switch to the RUN position.
2. Measure the voltage between sensor harness connector A and connector B.

Refer to Measuring Voltage in Wiring Systems.

Does the voltage equal the specified value?

5 V

Go to Step 3

Go to Step 6

3 |

1. Turn the ignition switch to the OFF position.
2. Connect the sensor.
3. Turn the ignition switch to the RUN position.
4. Use the Scan Tool to clear the DTC.
5. Cycle the ignition from the RUN position to the OFF position several times.

Did the DTC reset?

--

Go to Step 4

Go to Intermittents and Poor Connections

4 |

1. Inspect the terminals for proper terminal contact.

Refer to Intermittents and Poor Connections .

2. Replace the HVAC programmer if terminal contact is OK. Refer to Programmer Replacement .

Was the HVAC programmer replaced?

--

System OK

--

5 | Replace the sensor. Refer to Ambient Temperature Sensor Replacement . Is the repair complete? | -- | System OK | --
6 | Is the voltage greater than the specified value? | 5 V | Go to Step 7 | Go to Step 8
7 | Repair the short to the battery in CKT 735. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | System OK | --
8 | Measure the voltage between sensor terminal A and ground. Refer to Measuring Voltage in Wiring Systems. Does the voltage equal the specified value? | 5 V | Go to Step 9 | Go to Step 11
9 | Are all HVAC sensor DTCs present? | -- | Go to Step 10 | Go to Step 14
10 | Check CKT 1704 for an open. Refer to Testing for Continuity in Wiring Systems. Was an open found? | -- | Go to Step 14 | Go to Step 11
11 | Replace the heater and A/C programmer if CKT 1704 is OK. Refer to Programmer Replacement . Is the heater and A/C programmer replacement complete? | -- | System OK | --
12 | Measure the voltage between programmer terminal F8 (Buick,Oldsmobile) or terminal D8 (Pontiac) and DLC terminal 4. Refer to Measuring Voltage in Wiring Systems. Does the voltage equal the specified value? | 5 V | Go to Step 13 | Go to Step 4
13 | Repair the open in CKT 735 (GRN/BLK). Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | System OK | --
14 | Repair the open in CKT 1704. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | System OK | --