B1318

Schematic:

CIRCUIT DESCRIPTION
The sun load temperature sensor is a light sensitive photodiode that controls the signal voltage to the heater and A/C programmer. This photodiode is different from the standard thermistor sensors. The resistance measurements will not produce accurate results. The heater and A/C programmer monitors the voltage on CKT 590 to the sensor. When the sensor is in direct light the heater and A/C programmer reads a low signal voltage at pin C7. As the sensor becomes shaded, the signal voltage increases and voltage is pulled through sensor ground. The signal voltage varies between 5 V (open circuit) and 0 V (short circuit).

CONDITIONS FOR RUNNING THE DTC
^ Ignition is in the ON position.
^ Circuit is open.

ACTION TAKEN WHEN THE DTC SETS
A substitute temperature reading of 250 counts is implemented in order to continue the operation of the system. There will be no automatic compensation due to sunload.

NOTES ON INTERMITTENCE
If an intermittent DTC B1318 is set, use a Scan Tool in order to select the following settings:
^ Data list
^ Open/shorts data
^ Observe the reading

Manipulate the wiring while observing the Scan Tool. If a failure is induced, the reading will jump. Inspect for the following conditions:
^ A poor terminal contact
^ An obstructed or defective sensor

TEST DESCRIPTION

Steps 1-10:

1. Perform the HVAC Diagnostic System Check before continuing with the diagnosis of this DTC.
2. The Scan Tool displays the Sun Load Temperature Sensor reading. Jumping the harness connector determines if the wiring or the sensor is the cause.
3. The DMM checks for an open in the Sunload Temperature Sensor feed circuit.