08-14 Chevy Service Trailer Brake System light
When a vehicle, especially an 08-14 Chevy 2500 or Duramax has a service trailer brake system light on. It typically means somewhere within the circuit of the trailer brake harness there is one of the following:
- Loss of voltage before the trailer brake
- Short to ground
- Line to Line short
- Open relay
- Faulty switch
- Dirty connection
- Loose connection
It may seem daunting to attempt a repair within your truck’s wiring system, but take it from me. It is not that hard. At least try some of the solutions I’ve done to my trailer brakes back online…
I get it.. you hear it constantly. Seriously though let’s not turn this into a pain in the butt if we don’t have to.
- remove ground off the battery
This will ensure even if a line is going to the ground, it won’t make it back to the battery. I wish I had a picture from the other night… Smokey Smokey.
- Throw your E-brake on
- Make sure vehicle is in park
We do not need to lift the vehicle in any way unless your truck is lowered. For the rest of us let’s continue.
What tools do I need?
If you do not have the tools listed below, please go pick them up. It may seem silly investing in these tools right now, but they will pay you dividends for the next time.
- Electrical meter
- Wire cutters/strippers
- Flathead screwdriver
- Electrical M/F insulated connectors
- Miscellaneous butt connections
- Lighter/heat gun
- Wire nuts (grab an assorted pack – if you cannot find an assorted pack. Just opt for the blue wire nuts.)
Always the best practice is to check the little things first. I cannot count the amount of time where I get 4 hours into working on a vehicle, take a break, and then realize I haven’t even checked to see if I have ground.
Well, sure enough, we don’t have ground. Here’s what you do! Go pull off your trailer connector from the truck. Blow some compressed air in it, then dab some di-electric grease on the male side.
Okay, that didn’t work? Have you confirmed the vehicle has a good ground?
Grab your electric meter and place it into the continuity setting. This setting will give a tone when there is continuity between the piece you touch with your black lead and the piece you touch with your red lead (this work on metal type surfaces like wire, and steel).
For testing ground here are the 3 steps:
- Unhook both positive and ground from the battery terminal.
- Test continuity between the negative battery cable that was connected to the terminal and the block (make sure to find a spot that is not rusty, cleaner the better).
- Test continuity between your positive terminal that was connected to the battery terminal to the block.
No continuity between the negative battery cable and the engine block
Again make sure the places you are checking continuity to are ultra-clean and shiny. Passed that trace your negative battery cable back to where it is mounted to the frame or engine block. Ensure this is attached – pull it off. Clean it, clean the surface it was attached to.
Continuity between the negative battery terminal and the block
Awesome! Great start. Move to the next paragraph. Engine ground is important for the running of electronics within a vehicle. As a matter of fact, if you lose ground while even on the highway, the engine will shut off.
Continuity between positive cable and the block
This is a serious problem that needs to be addressed ASAP. At this point, if you’re not comfortable tracing wire back to look for line-to-ground shorts, I would look for a tow truck and auto repair shop.
Don’t let this discourage you. You can continue to work on the truck if you want to. Just make sure you know what you’re doing. Feeding a battery back 12v can seriously hurt you if it blows up. Many times you wouldn’t know you are feeding back voltage.
If it’s an intermittent short-to-ground situation, this will be an incredible task to track it down.
The next easiest step is to check for loose connections. Here are the steps:
- Grab the pin connector on your trailer
- Pull with medium/light for on each wire one by one
If wire connections are loose within the connection either replace the connection or if it’s not a sealed plug, open it up and tighten the connections.
- Look under your bumper on your truck
- Find the plug next to your license plate for the trailer pin connection
- Jiggle and shake the connections and see if any are loose
If they are loose refer to the last section for trailer pin connections.
Loss of voltage before the trailer brake
Next is to check if you even have 12 bolts going to the trailer connection on your Silverado. Grab your meter and make sure it’s in the DC meter setting. Find #4 pin and #1 pin. Place your black lead on #1 and red lead on #4. Does this read between 12-12.98v DC? Does it read any power? If not, that is an issue.
Find the trailer controller fuse within your fuse panel. The fuse panel is located under the hood in a black box. The specific fuse is labeled STUD #2. Pop it out and test continuity between the two connections. If you have continuity replace the fuse, if you do not have continuity then put a new fuse in and test power at the pin connections again. Another way to make sure you have 12v power on your trailer controller is to see if the display is on for the controller. If so you’ve got 12v.
Also, check this fuse. It’s located under the dash compartment in a fuse box. This fuse controls
This fuse controls power for trailer lights and vehicle 3rd brake light.
Short to ground
Let’s check short to ground on your vehicle trailer connection. Switch to continuity again on your meter. Now measure continuity between pin #1 (ground white) and pin #4 (black/red 12V) photo above.
If you have continuity between these connections, it means there is a line short to ground within the trailer braking system. Meaning 12v is energizing the ground of the vehicle and in return. Energizing the ground wire for your trailer system. Another test you can perform is testing DC voltage on pin #1 and the steel frame next to it. If you have voltage then, you know you have 12 volts energizing your ground.
Another reason you could have continuity between ground and power is a Direct short. Meaning somewhere within this system, the black/red wire and the ground wire rubbed together. Through the insolation and then finally the copper wire within touches together.
This could be especially frustrating, ensure you have stocked up on tons of fuses so you can diagnose safely.
Finally, you can check the trailer brake controller to continue relay assembly. This relay can be located on the driver’s side frame near the rear axle. This relay, from my understanding, receives the communications from the blue wire “electric brakes”, transcribes the electromagnetic feedback from the electric brake, communicates this to the controller. The controller will then send an inverted voltage back based on how much power to the trailer brakes is needed. So it’s a pretty serious part – if you have made it this far with no luck. This relay is worth a try. I believe it’s $30-$40 from Amazon, Autozone, advanced auto parts, and others.
AC Delco pt#20904439
AC Delco pt#20904439