im working on my 2009 chevy express cargo van, dealing with the issue of left turn signal both rear, front and brake light not working, just a fast flashing turn signal on the gauge cluster, the right side works just fine, I have checked all the bcm fuses under hood all looks good, I have checked for power at both the front and rear bulb sockets, I got no power coming there, also pull out the bcm, when back probing the output signal wire from the bcm to the left turn signal I got no power, I tried unplugging the connector then used my power prob to feed power to the wire circuit the bulbs do come on, could this be a bad bcm or does anyone know if this also could be caused by some thing else, please advice me before spend money on this expensive bcm. thanks.

 

Is the right signal getting to the BCM from the blinker switch?

https://charm.li/Chevy%20Truck/2009/...Schematic%202/

 

yes im getting the signal from right turn signal at the bcm..also when I turn the hazard light on only the right still works.

 

is there any way you can put a clamp on dc ammeter onto the hot wires that serve the non functional lights?
I had a similar problem on my chevy express 07 3500. I had no brake or reverse on the left, then later the turn signal left went out too. I temporarily jumped the hot wire for left brake and reverse from the hot wires on the right bulb assembly. I realized I needed a turn signal left so I had to fix it. when the turn signal left went out , I went used my VOM w dc amp clamp on capability to measure the current getting to the left side bulb assembly for each non working function. it turned out that the bulbs of my left side brake -reverse -turn signal bulb assembly was not getting enough amps that it needed to light up. the right side rear lights all worked fine for turn- brake- and reverse.. I measured the amps flowing into that right side bulb assembly for each of the functions of the right side: bulb- reverse, brake and turn. all worked, and the amp measurement into each was very very close to the rated amps printed on a new bulb package needed for the bulb to lite. then I switched the good rightside bulb into the non working left tail light assembly. nothing lit up. i measured the amps into each function on the left , for brake reverse turn: the amps into the left side assembly were getting about 1/2 of the amp current needed to light the bulbs that the rightsize bulb was getting. when I switched the working bulb out of the right side into the nonworking left side , nothing lit up. same result for brand new bulb that worked fine on right but no joy on left. my diagnosis was that the hot wires supplying the left side light assembly had been crimped or damaged so as to reduce amp current flow so much that the left side bulbs would not lite due to insufficient amps . I used a VOMeter with dc amp clamp on to diagnose this problem. I then tried to do an amp measurement on the left assembly hot wires, but tracing down to where the hot wire was damaged etc was a pain. so I sprung for a new rear left light assembly for about $75 bucks off the internet. installing the new left taillight complete assembly was easy. my theory is that all wires deteriorate and age and then deliver less current, though the voltage into the lamp assembly is constant. in my case the voltages at the left , measured for each bulb function, were fine , but the current into each function was too low to light the bulb. measuring proper voltage into the left side bulb was confusing me. using ohm's law E voltage in volts = I current in amps x R ohms of resistance in the wire. so I current in amps = E voltage divided by unknown ohms of resistance. so I could have equal voltages at each lamp assembly, left compared to right. but if the left side hot wires had more ohms of resistance, the amps of current getting through for the left side bulb assembly would be much less. I decided to replace the right taillight assembly too since they were both the same age. it's now about 4 years later and my rear lights are still working fine. PS- the chevy dealer estimated $1000 to fix this problem and I'd have to drop off the van and they'd 'et to it when they can. . ' . and was planning to rip apart the steering wheel and fuss with the turn signal stalk .

 

did you ever figure it out? I’m in the same boat

 

use a dc clamp on ammeter and see what current you are getting in to each bolt of the left rear lamp assembly.

see my old post of 5/12/24. a $75 new rear left lamp assembly fixed all my problems. I used a fluke w dc clamp on to measure input current to each Rear Left bulb, each current was insufficient to light the bulb.