B2578

CIRCUIT DESCRIPTION
The BCM monitors the RF turn signal circuit in order to determine the status of the turn signal switch. If the BCM detects an oscillating voltage on the RH turn signal monitor circuit, the BCM interprets this as a RF turn signal ON request from the turn signal switch. The BCM will then de-energize the RH DRL relay, which will disable the RF turn signal lamp (which is ON for the DRL), this allows the RF turn signal to flash. If the BCM does not detect an oscillating voltage on the RH turn signal monitor circuit, the BCM interprets this as the RF turn signal being OFF. The BCM will then energize the RH DRL relay and continue normal DRL operation. The BCM monitors the RH turn signal monitor circuit and determines how long voltage is applied. If the voltage is applied for longer than expected, a malfunction is present and a DTC will set.

CONDITIONS FOR SETTING THE DTC
^ The BCM detects continuous battery voltage on the RH turn signal monitor circuit.
^ The condition must be present for longer than 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
Stores a DTC B2578 in the BCM memory.

CONDITIONS FOR CLEARING THE DTC
^ This DTC requires an ignition cycle in order to change from current to history.
^ The BCM no longer detects continuous battery voltage on the RH turn signal monitor circuit for longer than 5 seconds.
^ A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
^ Use the IPC clearing DTCs feature.
^ The BCM receives the Clear Code command from the scan tool.

DIAGNOSTIC AIDS
^ The following conditions may cause an intermittent malfunction:
- There is an intermittent short to voltage in the RH turn signal monitor circuit.
- The turn signal switch or the hazard switch is internally shorted or is sticking.
^ The BCM needs to detect voltage oscillations on the RH turn signal monitor circuit in order to de-energize the RH DRL relay. If the BCM detects continuous voltage on the RH turn signal monitor circuit, the BCM interprets this as a short to voltage. The BCM will continue with normal DRL operation, and the RF turn signal will remain inoperative.
^ If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. Refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-2:

Steps 3-15:

The number(s) below refer to the step number(s) on the diagnostic table.
2. Tests if a DTC B2583 is stored in the BCM. If both the RH and LH turn signal monitor DTCs are stored, test the hazard switch and related circuits for a short to voltage.
3. Tests if the BCM is receiving oscillating voltage on the RH turn signal monitor circuit. If the test lamp is ON steady, the BCM will set a DTC B2578.
4. Tests if the BCM is receiving oscillating voltage on the RH turn signal monitor circuit. If the test lamp is ON steady, the BCM will set a DTC B2578.
5. Tests if the turn signal switch or related circuits are shorted to voltage.
6. Tests if the hazard switch or related circuits are shorted to voltage.
7. Tests if the instrument panel cluster turn signal indicator is shorted to voltage.
8. Tests if the body control module is shorted to voltage.