B1803

Step 1: Perform visual inspection of rear turn signal bulbs by removing bulbs from sockets and checking for broken filaments or blackened glass. Test bulb continuity with multimeter (should read 2-5 ohms across terminals when functional).

Step 2: Inspect bulb sockets for corrosion, melted plastic, or damaged terminals. Clean socket contacts with electrical contact cleaner and wire brush if corrosion is present. Check socket ground connection for continuity to vehicle chassis (should read less than 1 ohm).

Step 3: With bulb removed and ignition on, activate turn signal and measure voltage at bulb socket connector using multimeter. Should see battery voltage (12-14V) pulsing on/off. If no voltage present, proceed to check wiring.

Step 4: Backprobe the BCM connector at the turn signal output circuit (refer to wiring diagram) and measure voltage while activating turn signal. If voltage present at BCM but not at socket, trace and repair open circuit in wiring harness between BCM and rear lamp assembly.

Step 5: If voltage is present at socket and bulb tests good, check for proper ground path by measuring voltage drop between socket ground and battery negative (should be less than 0.5V with lamp operating). Repair ground connection if excessive voltage drop exists.

Step 6: After repairs, clear codes, cycle turn signals multiple times, and verify DTC does not return. Test both left and right rear turn signals for proper operation and flash rate.