GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Eldorado 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B1318

Circuit Description

The HVAC control processor monitors the outside light on the inside of the vehicle via a light sensitive photodiode which is called a sunload sensor. The HVAC control processor uses this information to compensate for the effect of the sun on the inside air temperature of the vehicle. When the sensor is in direct sunlight, the signal voltage is low. When the sensor is shaded, the signal voltage is high. The HVAC control processor requests A/C compressor clutch engagement and controls the air temperature actuator door positions in order to maintain the selected air temperature.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The HVAC control processor detects the signal circuit is greater than 250 counts (4.90 V).

Action Taken When the DTC Sets

A default value will be used for the sensor data by the HVAC control processor. The scan tool displays the default Solar Sensor value in the Heating and Air Conditioning Data list. The scan tool displays the actual Raw Solar Sensor value in the Heating and Air Conditioning, Open/Short Data list.

Conditions for Clearing the DTC
    • The DTC will become history if the HVAC control processor no longer detects a failure.
    • The history DTC will clear after 100 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Diagnostic Aids

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Tests for the proper operation of the circuit in the high voltage range.

    2.

  2. Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Raw Solar Sensor parameter in the Body, Heating and Air Conditioning, Open/Short Data list.

Does the scan tool display Open or short?

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn OFF the ignition.
  2. Disconnect the sunload sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Raw Solar Sensor parameter.

Does the scan tool display Open?

Go to Step 5

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the signal circuit of the sunload sensor and the low reference circuit of the sunload sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Raw Solar Sensor parameter.

Does the scan tool display Short?

Go to Step 6

Go to Step 8

5

Test the signal circuit of the sunload sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 9

6

Test the signal circuit of the sunload sensor for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 7

7

Test the low reference circuit of the sunload sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 9

8

Inspect for poor connections at the harness connector of the sunload sensor. 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 12

Go to Step 10

9

Inspect for poor connections at the harness connector of the HVAC 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 12

Go to Step 11

10

Replace the sunload sensor. Refer to Sun Load Sensor Replacement .

Did you complete the replacement?

Go to Step 12

--

11

Important:  Perform the recalibration procedure for the HVAC control processor.

Replace the HVAC control processor. Refer to HVAC Control Processor Replacement .

Did you complete the replacement?

Go to Step 12

--

12
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK