B1398

CIRCUIT DESCRIPTION
The body control module (BCM) provides a constant output reference voltage of 5 volts for the proper operation of the ambient light sensor. The constant output reference voltage supply ensures that variations in the output signal of the ambient light sensor are due to changes of the sensor rather than variations in the voltage supply. The BCM monitors the constant output reference voltage and sets a DTC when the output is not within the expected range of 4.75 - 5.25 volts.

CONDITIONS FOR RUNNING THE DTC
- The system voltage must be between 9.0 and 16.0 volts.
- The ignition switch must be in the RUN position.
- The park brake must be released.
- The headlamp switch must be in the AUTO position.

CONDITIONS FOR SETTING THE DTC
The voltage of the 5 V reference circuit must be above 5.25 V for 0.5 seconds.

ACTION TAKEN WHEN THE DTC SETS
The daytime running lamps (DRL) feature will not operate.

CONDITIONS FOR CLEARING THE DTC
- The DTC will clear on current status after the condition for setting the fault is corrected.
- A history DTC will clear after 100 consecutive ignition cycles without a fault present.

DIAGNOSTIC AIDS
- A short to voltage in the 5V reference circuit will only cause this DTC to be set.
- Perform a visual inspection for loose or poor connections at all related components.

Refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-3:

Steps 4-13:

The number(s) below refer to the step number(s) on the diagnostic table.
2. Tests for the proper operation of the circuit in the low voltage range.
3. Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
4. Tests for a short to voltage in the 5 volt reference circuit.