Left Turn Signal Failure

Samari21 · February 28

I have the left turn indicator failure. I’ve changed bulbs, harness, checked the grounds, checked the trailer brake and changed the fuse. I’m genuinely lost at this point. Could it be within the ECU?

Edited February 28 by Samari21

davester · March 1

no, it's not the ecu. do some electrical testing, to find where the problem is. a subscription to alldata.com for your truck will help with wiring diagrams and connector pinouts.

carkhz316 · March 1

Which one? Front or rear? If rear, and the lamp itself is illuminating properly, then its a failed BCM. I've replaced many for the rear lamp failure in working/ non-working lamp instances. The BCM directly controls the rear brake/ turn combo with no fuse or relay in line.

Samari21 · March 1

Left rear.

Samari21 · March 1

2 hours ago, carkhz316 said:

Which one? Front or rear? If rear, and the lamp itself is illuminating properly, then its a failed BCM. I've replaced many for the rear lamp failure in working/ non-working lamp instances. The BCM directly controls the rear brake/ turn combo with no fuse or relay in line.

Isn’t the BCM near the steering column?

davester · March 1

Yes, it is near the steering column. It is much more likely to be a wiring or connector problem elsewhere, and not the bcm. For pretty much every diagnostic procedure gm has for fixing everything in your truck, replacing one of the computers is one of last things to do.

carkhz316 · March 1

Is the brake light/ turn signal bulb working on the left side rear? BCM failure is not uncommon for random, trivial concerns as this in the K2 platform for some reason. As mentioned, the rear lamps are directly controlled by the BCM. If there ever is a wiring problem, such as a short to ground, the driver for the rear lights will eventually be destroyed. Why there is no fused protection is beyond me, but it is what it is.

Edited March 1 by carkhz316

Samari21 · March 2

3 hours ago, carkhz316 said:

Is the brake light/ turn signal bulb working on the left side rear? BCM failure is not uncommon for random, trivial concerns as this in the K2 platform for some reason. As mentioned, the rear lamps are directly controlled by the BCM. If there ever is a wiring problem, such as a short to ground, the driver for the rear lights will eventually be destroyed. Why there is no fused protection is beyond me, but it is what it is.

Yes, all of the lights work. The right side is fine. Only the left side is “failed.”

davester · March 3

...while the circuit is connected to the bcm, power to the bcm is fused, so it is not an unfused circuit.

Samari21 · March 3

10 hours ago, davester said:

...while the circuit is connected to the bcm, power to the bcm is fused, so it is not an unfused circuit.

Can you explain that to dummy like me? I’m not very experienced with electrical lol

davester · March 3

the bcm does not generate electricity itself, it gets power from the battery/alternator through a fuse (well, a number of fuses), and then connects that power to the lights or other things at the right time. So, if, say, a light circuit that is controlled by the bcm has a short, that would/should blow one of the fuses going to the bcm (and not melt the bcm or wiring because it's not fused).

Samari21 · March 12

After checking fuses, grounds, changing bulbs and harnesses and doing the “resets,” to no avail, I am humbly going to take my truck to the shop. I’m at a total loss now. I’m sure it’s the BCM. Is there anything I’m forgetting to try first?

MikeBMW · March 12

2 hours ago, Samari21 said:

After checking fuses, grounds, changing bulbs and harnesses and doing the “resets,” to no avail, I am humbly going to take my truck to the shop. I’m at a total loss now. I’m sure it’s the BCM. Is there anything I’m forgetting to try first?

Is your battery good and pushing out proper voltage?
Other than that, I hope you can get a reasonable solution.

Samari21 · March 12

7 hours ago, MikeBMW said:

Is your battery good and pushing out proper voltage?
Other than that, I hope you can get a reasonable solution.

Yep. Battery is roughly 4 months old.

GMCustomerService · March 16

We'd like the opportunity to connect further so we can help resolve these electrical difficulties with your turn signal alongside your dealer's support. For our assistance, kindly send us an email with these details to [email protected]. Please be sure you include "Samari21 GM Trucks Forums" in the subject line of your outreach. Your cooperation is much appreciated.