B1398

Circuit Description
The Body control module (BCM) provides a constant output reference voltage (5 volts) in order to enable correct 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 (5 volts) and sets a DTC when the output is not within the specified range (4.75 - 5.25 volts).

Conditions for Setting the DTC
- When the ignition switch is in the RUN position, the 5 volt reference output (CKT 705) is greater than 5.25 volts (shorted to battery).
- The system voltage is between 9.0 - 16.0 volts.
- The above conditions exist for 0.5 seconds.

Action Taken When the DTC Sets
The daytime running lamps feature will not operate.

Conditions for Clearing the MIL/DTC
- DTC B1398 will clear immediately after the condition that sets the DTC is corrected.
- A history DTC will clear after 100 consecutive ignition cycles without a fault present. History and current DTG(s) may be cleared using the scan tool.

Diagnostic Aids
- Always diagnose the first DTC that is listed on the scan tool.
- Verify that the scan tool displays DTC B1398 as a current code before you perform diagnostics.
- A short to battery voltage on CKT 705 will cause DTC B1398 to set.
- Inspect for loose or poor connections at all of the related components.
- Refer to Intermittents and Poor Connections Diagnosis in Overall Vehicle Information / Testing and Inspection.

Steps 1 - 3:

Steps 4 - 5:

Test Description
The number below refers to the step number on the diagnostic table.
2. This step determines if either of the following conditions exists:
- BCM is defective.
- CKT 705 is shorted to battery voltage.