Circuit Description
The Body Control Module (BCM) controls all exterior lamps by supplying power from the exterior lamp power circuit to the high side of the park lamp relay and the low beam relay coils. The BCM commands the exterior lamps ON by grounding the park lamp relay and the low beam relay. During this time battery voltage is present at the exterior lamp power circuit.
Conditions for Setting the DTC
| • | When the BCM attempts to send voltage out the exterior lamp power circuit an internal monitor will detects low voltage ,short to ground. The BCM can only test for this condition when the exterior lamp power is active. |
| • | The condition must be present for 300 ms. |
Action Taken When the DTC Sets
| • | The BCM attempts to reactivate the exterior lamp power every 1.2 seconds until the request is no longer required. |
| • | Stores a DTC B1970 in the BCM memory. |
Conditions for Clearing the DTC
| • | The exterior lamps power circuit is high when commanded ON. |
| • | The conditions for setting the DTC are no longer present. |
| • | A history DTC will clear after 50 consecutive malfunction free ignition cycles. |
| • | The BCM receives the clear code command from the scan tool. |
Diagnostic Aids
| • | Refer to the relay box end view for terminal assignments when the diagnostics direct you to take electrical measurements at the relay box. The end view is located in Power and Grounding Component Views in Wiring Systems. |
| • | Check the following if the problem is intermittent: |
| - | A damaged wiring harness. Inspect the wiring harness for damage. |
| - | If the wiring harness appears to be in good condition, observe the display on the DMM while moving connectors and wiring harnesses related to the BCM. |
| - | Inspect the wiring harness connectors for backed out terminals, improper mating, improperly formed or damaged terminals, and poor wire terminal to wire connections. |
| • | For additional information, refer to Inducing Intermittent Fault Conditions in Wiring Systems. |
Test Description
The following numbers refer to the numbers on the diagnostic table:
-
This step tests for the exterior lamp power at the exterior lamp power circuit of the low beam relay. A voltage test is made at the furthest point of the circuit to determine if the circuit is complete.
-
After verifying the BCM is sending voltage to the low beam relay, test the BCM again to see if the DTC resets indicating an internal failure.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Exterior Lights Schematics | ||||
1 | Did you perform the Lighting System Diagnostic System Check? | -- | Go to Step 2 | |
Is the measured voltage within the specified value? | 10-12 V | Go to Step 3 | Go to Step 4 | |
Is a current DTC B1970 set? | -- | Go to Step 5 | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | |
4 |
Did you find an correct the condition? | -- | Go to Step 6 | -- |
5 |
Important: Preform the programing procedure for the BCM. Replace the BCM. Refer to Body Control Module Replacement in Body Control System. Is the replacement complete? | -- | Go to Step 6 | -- |
6 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
