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
| • | The 5 volt reference output (CKT 705) is less than 4.75 volts (shorted to ground). |
| • | 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
| • | A current DTC 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 DTCs can 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 B1397 as a current code before you perform diagnostics. |
| • | A short to ground in CKT 705 will cause DTC B1397 to set. |
| • | Inspect for loose or poor connections at all of the related components. |
| • | Refer to Intermittents and Poor Connections Diagnosis for intermittent and poor connections. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the BCM 5 volt reference output voltage is shorted internally. Other DTCs will set when you disconnect the BCM connector.
-
This step determines if one of the following conditions exists:
| • | The ambient light sensor is shorted to ground. |
| • | CKT 705 (GRY) is shorted to ground between the sensor and the BCM. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the BCM Diagnostic System Check performed? | -- | Go to Step 2 | |
Does the scan tool display DTC B1397? | -- | Go to Step 6 | Go to Step 3 | |
Does the scan tool display DTC B1397? | -- | Go to Step 5 | Go to Step 4 | |
4 | Replace the ambient light sensor. Is DTC B1397 set as a current code? | -- | Go to Step 7 | -- |
5 | Locate and repair the short to ground in CKT 705 (GRY) between BCM connector C3 (PPL) and the ambient light sensor. Is the repair complete? | -- | Go to Step 7 | -- |
6 |
Is the repair complete? | -- | Go to Step 7 | -- |
7 | Clear the DTCs. Is the repair complete? | -- | -- |
