Circuit Description
The body control module (BCM) controls the headlamp relay. The BCM grounds the headlamp relay coil control circuit, which energizes the headlamp relay.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2578 Headlamp Control Circuit High
Conditions for Running the DTC
The BCM must be commanding the headlamp relay to energize.
Conditions for Setting the DTC
| • | The BCM detects a short to battery in the headlamp coil control circuit when the BCM tries to energize the headlamp relay. |
| • | The condition above must be present for more than 0.3 seconds. |
Action Taken When the DTC Sets
The BCM stores DTC B2578 in memory.
Conditions for Clearing the DTC
| • | A current DTC B2578 will clear if the BCM no longer detects a short to battery in the headlamp relay coil control circuit. |
| • | A history DTC B2578 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present. |
Diagnostic Aids
| • | If the DTC B2578 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | The following conditions may cause an intermittent malfunction to occur: |
| - | An intermittent short to battery in the headlamp relay coil control circuit |
| - | The headlamp relay coil is intermittently shorted to battery internally. |
| - | The BCM is intermittently shorted to battery internally. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Does the headlamp 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 headlamp relay control circuit for a short to battery positive voltage or an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
7 | Test the headlamp relay control circuit for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
8 | Inspect for poor connections at the headlamp relay. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
9 | Inspect for poor connections at the harness connector of the body control module. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
10 | Replace the LH accessory wiring junction block. Refer to Instrument Panel Electrical Center or Junction Block Replacement - Left Side in Wiring Systems. Did you complete the replacement? | Go to Step 13 | -- |
11 | Replace the headlamp relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | Go to Step 13 | -- |
12 | Replace the body control module. Refer to Control Module References in Computer/Integrating Systems 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 |
