Fault phenomenon: left rear turn signal is off.
Check and analysis: First test the car, verified the fault phenomenon. When slide turn signal switch connect the right turn signal, right front, right rear and right fender turn signal all can normally lit; slide turn signal switch connect the left turn signal, left front, left fender turn signal all can normally lit; but left rear turn signal is off.
Connect Ford VCM IDS read fault code, no fault code stored. Accordance with the principle from simple to complex, first check the left rear turn signal lamps. Remove the left rear taillight check the turn signal lamps, lamp is good. Use test light to measured turn signal lamps end connector terminal, when turned on the left turn signal, the test light does not shine. Then consult the relevant circuit diagram of this vehicle that the car's left rear turn signal is powered by the body control module (BCM) and left rear reversing lights, brake lights and marker lights sharing the grounding line.
Because the car's rear brake lights, marker lights and reversing lights are normal, so can rule out ground line poor caused left rear turn signal does not shine, so fault point is locked in left rear turn signal supply line. Remove the left front A-pillar trim, measured left rear turn signal F14 power fuse is good. Then measured with a multimeter from BCM to the left rear turn signal power line turned on situation, this line has good continuity. Thereby determining the failure is caused by BCM damage.
Troubleshooting: Replace the BCM. Test, everything is normal. The fault is cleared.
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