B1804

Step 1: Perform visual inspection of rear turn signal lamp assembly, socket, and bulb for signs of corrosion, moisture, melted plastic, or physical damage. Remove bulb and inspect socket terminals for discoloration or shorting. Check for aftermarket LED bulbs or resistors.

Step 2: Disconnect the rear turn signal lamp connector at the lamp assembly. Using a digital multimeter set to DC voltage, backprobe the BCM output wire at the harness side connector while turn signal is OFF. Reading should be 0V; if battery voltage (12V+) is present, the short is in the wiring harness between BCM and lamp.

Step 3: With lamp still disconnected, trace the rear turn signal wiring harness from lamp socket toward BCM, inspecting for pinch points at trunk/tailgate hinges, body seams, trailer hitch mounting areas, and any aftermarket wiring splices. Look for bare wire, chafed insulation, or contact with positive battery cables.

Step 4: If wiring harness shows no visible damage, disconnect BCM connector and check for battery voltage on the turn signal output pin with ignition OFF. Voltage present indicates wiring harness fault; no voltage indicates BCM internal short.

Step 5: Repair or replace damaged wiring/connectors, or replace faulty lamp socket. If BCM is faulty, verify by substituting known-good BCM or consulting manufacturer TSBs. Clear codes, reconnect all components, and verify turn signal operation through multiple cycles.

Step 6: Road test vehicle and activate turn signals in both directions multiple times. Monitor for code return using scan tool active monitoring of BCM turn signal output status to confirm repair success.