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View Full Version : Using Brake Controller Only Causes Red Brake Warning Light to Light Up


thorn
02-16-2016, 11:49 PM
I'm using a Tekonsha P3 brake controller with a horse trailer and when I pull the level over to apply power
to the trailer brakes (manually), the Sprinter red brake warning light comes on. The warning light is under
the speedometer and will go off once I turn the Sprinter off and back on. Any ideas? Thanks.

sailquik
02-17-2016, 12:36 AM
thorn,
Did you order the OEM Trailer wiring and towing cross member?
Did you find the green trailer brake controller connector in the driver's side seat box, and did
you connect your Teknosha P3 to a correctly wired 4 wire pig tail harness with the mating green connector?
Have you tried any other trailers (with electric brakes) to see if it's in the Sprinter wiring or in the trailer wiring.
I had a problem when I first got my current Sprinter, and it turned out to be in the trailer, not the OEM Sprinter
trailer towing harness.
I would also take a VOM meter and Ohm out the brake controller. See if it shows zero (0) resistance (a dead short) when you slide
the manual apply lever all the way.
May be that the Sprinter system is seeing a dead short and throwing a code.
I use the Valley Towing Products Odyssey and I can pretty much lock the trailer wheels if I fully apply the manual over ride.
Hope this helps,
Roger

thorn
02-17-2016, 01:53 AM
I got the green plug from MB and made up a cable and hooked it up in Dec. The trailer brakes work fine even using the manual lever, it will brake and stop it. I adjusted the P3 so it won't lock up the trailer brakes. They have a max scale, 12. Mine will lock up at 4-5 (depending on the load) so I adjusted the P3 so it won't go over 4. When I brake normally it will go up to 2 and if I break hard to 3 (it senses velocity and brakes more when you hit the brakes harder). If I don't use the lever, which I rarely do, the red light has not come on so far. So, I recently used the lever since I had the trailer loaded with 3 horses to see how much I need to slow it.

I do have the travel trailer I can try. The Tundra works fine with both trailers and I also have the P3 in it. I can check with my volt/ohm meter when I get a chance.

The P3 has 3 "boost modes" (normal - B1, B2 & B3) that will output more "power" to the brakes early on when you first apply the brakes. With the Sprinter I have it on B3 when the trailer is fully loaded. If I did that with the Tundra it would brake too much or too hard. I had to replace the front brakes on the Tundra (45k miles). It must not be applying as much power/volts to the trailer as it should. So I started on B1 but sometimes that feels like too much on th trailer. I wish I could fine tune that but it's built into the P3. I'm not sure why B3 works OK for the Sprinter, B3 is for larger trailers.

The P3 I got for the Sprinter in Oct. clicks when I use the lever, must be some sort of relay. The one on the Tundra is 5 years older and does not click when I use the lever. I wonder if they changed the design.

Thanks, Greg

thorn,
Did you order the OEM Trailer wiring and towing cross member?
Did you find the green trailer brake controller connector in the driver's side seat box, and did
you connect your Teknosha P3 to a correctly wired 4 wire pig tail harness with the mating green connector?
Have you tried any other trailers (with electric brakes) to see if it's in the Sprinter wiring or in the trailer wiring.
I had a problem when I first got my current Sprinter, and it turned out to be in the trailer, not the OEM Sprinter
trailer towing harness.
I would also take a VOM meter and Ohm out the brake controller. See if it shows zero (0) resistance (a dead short) when you slide
the manual apply lever all the way.
May be that the Sprinter system is seeing a dead short and throwing a code.
I use the Valley Towing Products Odyssey and I can pretty much lock the trailer wheels if I fully apply the manual over ride.
Hope this helps,
Roger