Left front turn signal light not working properly

2015 GMC SIERRA
103,000 MILES • 6.6L • V8 • TURBO • 4WD • AUTOMATIC
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TRAVIS ROSS
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When I unlock the truck the left orange turn signal bulb flashes so I know it's working but once I start the truck the light doesn't work anymore. Wondering why it's not staying on while the truck is running?
Nov 17, 2020 at 7:33 AM
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KASEKENNY
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So it is just the left front turn signal that is not working? The rear does work when you turn the signal on?

If that is the case, we need to start the engine and turn the turn signal on. Then go to the relay in the under hood fuse block and remove it and check for ground on pin 85. To do this, clip your test light on battery positive and then use the probe to pin 85. Does the test light come on?

If not the BCM is not grounding the relay and the BCM is the issue. Clearly everything works since the light can flash but the BCM uses a difference internal circuit to the BCM to flash the light through the security system vs the turn signal. So I am pretty confident that the BCM is the issue.

Let me know what questions you have and we can go from there. Thanks
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Nov 17, 2020 at 8:13 AM