B1802

Step 1: Perform visual inspection of rear turn signal lamps - check for burnt bulbs, damaged sockets, melted connectors, or obvious corrosion. Test bulb operation by manually activating turn signals and observing which side fails to illuminate.

Step 2: Using a digital multimeter, back-probe the turn signal lamp connector with ignition on and turn signal activated - verify presence of battery voltage (12-14V) at the signal wire. If voltage is present but lamp doesn't illuminate, suspect bulb/socket/ground. If no voltage, proceed to Step 3.

Step 3: Check continuity between BCM turn signal output pin and the rear lamp connector with harness disconnected at both ends using multimeter ohmmeter function - reading should be less than 5 ohms. Check for shorts to ground (infinite resistance to chassis ground) and shorts to power (no voltage present with key on).

Step 4: Locate and inspect rear lighting ground point (typically body panel or frame rail near tail lamp assembly) - remove ground bolt, clean contact surfaces with wire brush, check for corrosion, and verify less than 1 ohm resistance to battery negative terminal.

Step 5: If all wiring, grounds, and bulbs test good, use bidirectional controls in scan tool to command BCM to activate the affected turn signal circuit while monitoring voltage at BCM connector - this isolates whether BCM output driver has failed internally.

Step 6: After repairs, clear codes and perform operational test of all turn signal functions (left, right, hazards) for at least 10 complete cycles to verify fault is corrected and code does not return.