Circuit Description
The body control module (BCM) controls all exterior lamps by supplying power from terminal B10 to the high side of the park lamp and the low beam relay coils. The BCM commands the exterior lamps On by grounding the appropriate relay at either terminal C9 or terminal C12. During this time battery voltage is present at terminal B10.
Conditions for Setting the DTC
| • | The BCM attempts to send voltage out terminal B10 but an internal monitor detects low voltage (short to ground). The BCM can only test for this condition when the exterior lamp power is active (for example, during a headlamp ON request). |
| • | 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 conditions for the fault are no longer present. |
| • | The use of a scan tool. |
| • | A history DTC will clear after 50 consecutive ignition cycles if the condition for the fault is no longer present. |
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. |
| • | Test 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 Intermittents and Poor Connections Diagnosis 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 terminal 3. 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 terminal 3, test the BCM again to see if the DTC resets indicating an internal failure.
-
This step tests for a possible intermittent condition. Moving the wires to the relay box and BCM may cause the fault to reappear.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the BCM Diagnostic System Check? | -- | Go to Step 2 | |
Is the measured voltage within the specified range? | 10-12 V | Go to Step 3 | Go to Step 4 | |
Is a current DTC B1970 set? | -- | Go to Step 5 | Go to Step 8 | |
4 |
Is the measured resistance at the specified value? | OL | Go to Step 6 | Go to Step 7 |
5 | Replace the BCM. Refer to Body Control Module Replacement . Is the replacement complete? | -- | Go to Step 8 | -- |
Monitor the meter while moving the wiring to the relay box and the BCM. Did the DMM indicate a short to ground? | -- | Go to Step 7 | Go to Step 5 | |
7 | Locate and repair the short to ground in CKT AM810 or CKT AM811. Is the repair complete? | -- | -- | |
8 |
Does the BCM operate properly? | -- | System OK |
