Circuit Description
The body control module (BCM) controls the headlamp relay by grounding the control circuit of the headlamp.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2577 Headlamp Control Circuit Low
Conditions for Running the DTC
Voltage supplied to the module is in the normal operating voltage range, approximately 9-16 volts.
Conditions for Setting the DTC
| • | The BCM detects a short to ground or an open in the control circuit of the headlamp relay coil or the low beam headlamp control circuit relay when the BCM is not energizing the headlamp relay. |
| • | The condition is present for more than 3 ms. |
Action Taken When the DTC Sets
| • | The BCM stores DTC B2577 in memory. |
| • | The SERVICE VEHICLE SOON telltale illuminates. |
| • | With the ignition in the RUN position, the BCM deactivates the daytime running lamps and turns on the park lamps. |
Conditions for Clearing the DTC
| • | A current DTC B2577 clears if the BCM no longer detects a short to ground or an open in the control circuit of the headlamp relay control circuit of the low beam relay headlamp control circuit. |
| • | A history DTC B2577 clears after 100 consecutive ignition cycles. |
| • | The BCM receives the Clear Code commend from the scan tool. |
Diagnostic Aids
| • | If the DTC B2577 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections . |
| • | An intermittent short to ground or an open in the following locations may cause an intermittent malfunction to occur: |
| - | The low beam headlamp relay control circuit |
| - | The headlamp relay control circuit |
| - | The headlamp relay |
| - | The BCM |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference: Master Electrical Component List | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
2 |
Does the HDLP low-beam relay turn ON and OFF with each command? | Go to Diagnostic Aids | Go to Step 3 |
3 |
Does the test lamp illuminate? | Go to Step 4 | Go to Step 10 |
4 |
Does the test lamp turn ON and OFF with each command? | Go to Step 8 | Go to Step 5 |
5 | Does the test lamp remain illuminated with each command? | Go to Step 7 | Go to Step 6 |
6 | Test the control circuit of the HDLP low beam relay and the headlamp control circuit for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
7 | Test the control circuit of the HDLP low beam relay and the headlamp relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
8 | Inspect for a poor connection at the HDLP low-beam relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
9 | Inspect for a high resistance at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
10 | Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement . Did you complete the repair? | Go to Step 13 | -- |
11 | Replace the HDLP low beam relay. Refer to Relay Replacement . Did you complete the replacement? | Go to Step 13 | -- |
12 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 13 | -- |
13 |
Does the DTC reset? | Go to Step 2 | System OK |
