Trailer Brakes Do Not Engage While Towing With 2012 Toyota Sienna  

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Expert Reply:

I took a look at the owner's manual for the 2012 Toyota Sienna and was not able to find a fuse location dedicated to trailer brakes. There was a fuse location for trailer lights but not brakes. It makes sense that the fuse location does not exist because the 2012 Toyota Sienna only came pre-wired for a 4-flat trailer connector from the manufacturer not a 7-way connector like what is needed to power trailer brakes with a brake controller.

It sounds like you may have a 7-way connector hardwired on the Sienna. To find out why the trailer brakes are not engaging the first step is to inspect the 7-way pins for corrosion, damage or dirt. If the brake output pin is bent or damaged the trailer brakes may not engage. I also recommend to check the ground wire on the 7-way connector to make sure it is ground to a clean bare metal surface. We have found that corrosion and ground problems are the reason for malfunction in most of our wiring situations.

If all of your pins are clean, not damaged and the ground is okay then it sounds like you have a short on the brake output wire somewhere between the brake controller and the trailer brakes. Check the brake output pin on the 7-way vehicle connector with a circuit tester like part # PTW2993 while someone applies the manual override on the brake controller. I have attached a photo that shows the pin positions of a standard vehicle 7-way for your reference.

If the circuit tester is fully illuminated then you are getting full voltage to the pin on the vehicle side and the issue is on the trailer's side wiring. Check the brake output wire (most commonly a blue wire) on the trailer side for frayed or damaged wiring. You also want to check the grounds on the braking assemblies to make sure they are properly grounded to a clean bare metal surface on the trailer's frame.

If the circuit tester is not showing full power (dimly lit) at the brake output pin or no power at all, then the brake output wire between the brake controller and the vehicle's 7-way is the issue. Since your 7-way is hardwired on the Sienna, you want to check all of your connections at the back of the brake controller to make sure they are not loose. Check all of your connections from the brake controller, especially the stop light switch. Check the ground the brake controller as well. You also want to make sure the 12V power is properly connected to the battery.

The last step if you are still having trailer brake issues after you checked the connections, is to test the blue wire from the back of the brake controller. You can cut the blue wire 6 inches back from the brake controller to test for voltage. If you do not have proper voltage there, the brake controller needs to be replaced. I do not think you will need to go this far because like I said a lot of wiring issues comes down to the ground or corrosion on the 7-way pins.

expert reply by: Heather A

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