DTC 021

CIRCUIT DESCRIPTION
The body control module (BCM) supplies battery voltage to the courtesy lamps through the courtesy lamps supply voltage circuit when the BCM is awake. When the BCM sees the proper inputs it will ground the courtesy lamps low control circuit, and the courtesy lights will illuminate.

CONDITIONS FOR RUNNING THE DTC
The BCM must command the courtesy lamps ON.

CONDITIONS FOR SETTING THE DTC
^ The BCM detects that the output for the courtesy lamps supply voltage circuit is low when it is expected to be high.
^ There is an open or short to ground in the battery positive voltage circuit to the BCM that feeds the courtesy lamps supply voltage circuit.
^ The condition above must be present for more than 0.3 seconds.

ACTION TAKEN WHEN THE DTC SETS
The BCM stores DTC B21/31 in memory.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC B21/31 will clear if a short to ground or open in the courtesy lamps supply voltage circuit is no longer detected by the BCM.
^ A current DTC B21/31 will clear if the open or short to ground in the battery positive voltage circuit to the BCM that feeds the courtesy lamps supply voltage circuit is no longer present.
^ A history DTC B21/31 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present and no other BCM faults are detected.

DIAGNOSTIC AIDS
^ If the DTC B21/31 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ The following conditions may cause an intermittent malfunction to occur:
- An intermittent short to ground or open in the courtesy lamps supply voltage circuit
- An intermittent open or short to ground in the battery positive voltage circuit to the BCM that feeds the courtesy lamps supply voltage circuit
- An intermittent short to ground in a courtesy lamp
- The BCM is intermittently shorted to ground or open

TEST DESCRIPTION

Steps 1-4:

Steps 5-11:

The numbers below refer to the step numbers on the diagnostic table.
2. Test for voltage at the courtesy lamps supply voltage circuit. No voltage at the courtesy lamps supply voltage circuit would indicate that the fault is current, voltage at the courtesy lamps supply voltage circuit would indicate that the fault is intermittent.
3. Verifies that the COURTESY Fuse is good, an open fuse indicates a short to ground in the courtesy lamps supply voltage circuit or the battery positive voltage circuit of the BCM, that feeds the courtesy lamps supply voltage circuit.
4. Verifies that the battery positive voltage circuit of the BCM is providing battery voltage.