For 1990-2009 cars

### Circuit Description

The calibrations for the heater and A/C control are stored in EEPROM. When the ignition is first turned On, the controller performs internal tests on the EEPROM to determine if the EEPROM is programmed.

### Conditions for Setting the DTC

• | The test byte in EEPROM has an incorrect value (EEPROM not programmed).

• | This fault is immediately recognized when the ignition is first turned On.

### Action Taken When the DTC Sets

• | Stores a DTC 52 in the controllers memory.

• | The heater and A/C control uses default values.

### Conditions for Clearing the DTC

• | Programming the heater and A/C control.

• | The use of a scan tool.

• | A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. Calibrations for the heater and A/C control module are stored in EEPROM. Because this DTC sets when a test byte is incorrect in EEPROM, this step reprograms the module.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the HVAC Systems Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check
2 |

1. Install a scan tool.
2. Select PROGRAMMING from the Heating and Air Conditioning menu.
3. Follow the programming instructions on the display screen.

Did you complete the programming procedure?

--

Go to Step 3

--

3 |

1. Turn OFF the ignition.
2. Turn ON the ignition, with the engine OFF.
3. Access DTCs using the scan tool.

Does the scan tool indicate that DTC 52 is current?

--

Go to Step 4

Go to Step 5

4 | Replace the heater and A/C control module. Did you complete the replacement? | -- | System OK | --
5 | Use the scan tool in order to clear DTCs. Did you complete the repair? | -- | System OK | --