Circuit Description
The body control module (BCM) monitors CKT 278 in order to determine if either of the following lamps should be turned ON when the headlamp and panel dimmer switch is in the AUTO mode:
| • | The daytime running lamps (DRL) |
| • | The headlamps |
The DRL will be commanded ON when the following conditions exist:
| • | The BCM senses that the ambient light sensor voltage is between 2.2-4.7 volts. |
| • | The sensor resistance is low. |
The headlamps will be commanded ON if the following conditions exist:
| • | The BCM senses the ambient light sensor voltage is between 0.2-1.3 volts. |
| • | The sensor resistance is high. |
If the BCM senses voltage on CKT 278 above 5.25 volts, the BCM will set DTC B2648.
Conditions for Setting the DTC
| • | The ambient light sensor voltage is greater than 5.0 volts, which indicates that CKT 278 is 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 automatic headlamp control will remain ON in any ambient light state.
Conditions for Clearing the MIL/DTC
| • | This DTC will clear immediately when the short to battery is no longer detected. |
| • | A history DTC will be cleared after 100 consecutive ignition cycles without a fault present. |
| • | History and current DTCs can be cleared using a scan tool. |
Diagnostic Aids
| • | Always perform the first DTC that is listed on the scan tool if more than one is displayed. |
| • | Verify that the scan tool displays DTC B2648 as a current code before you perform diagnostics. |
| • | Inspect for loose or poor connections at all of the related components. |
| • | Refer to Wiring Systems for intermittent and poor connections. |
Test Description
The number below refers to the step number on the diagnostic table.
| • | The BCM is defective. |
| • | CKT 278 is shorted to battery voltage. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the BCM Diagnostic System Check performed? | -- | Go to Step 2 | |
Does the scan tool display B2648 as current? | -- | Go to Step 4 | Go to Step 3 | |
3 | Locate and repair the short to battery in CKT 278 (WHT) between the ambient light sensor and the BCM. Is the repair complete? | -- | Go to Step 5 | -- |
4 |
Is the repair complete? | -- | Go to Step 5 | -- |
5 | Clear the DTCs. Is the repair complete? | -- | -- |
