Brake Controller Troubleshooting/Technical Info

[Tom2531]

This post is about the brake controller on the 2021 HD Ram. First, my story. Second some reverse engineering and description of the warnings on the dash. Finally, some technical details. I would assume this information would apply to other years in the same generation of truck, but outside of that, I don’t know.

I was greeted with Check Trailer Brake Wiring/Trailer Brake Disconnected on our first trip out with our 2021 2500 and travel trailer combo. The same trailer on our 2018 1500 had no issues earlier in the year. At first it happened after a few hours. Sometimes it would just say Check Trailer Brake Wiring, and other times it would ding and say Trailer Brake Disconnected. I read this related post: Trailer Brake Disconnected. I found I had the “old” style 7 pin connector, and I needed to extend mine anyway – so I ordered a Hopkins HM20048 and put that on. The first time I plugged it in, I had no brakes and no left turn signal on the trailer. I bent the pins a little and got them working. Unfortunately, after a short while on the next trip, the error returned.

What bothered me is the error wasn’t real helpful. I wasn’t sure if I had a short, break, or something intermittent. Nor did I know if the problem was in the truck or trailer. I went about troubleshooting and here is what I learned.

Brake Controller Operation​

In the rest of this post, I will refer to the two warning messages and accompanying indicators/audibles as CTBW and TBD.

• CTBW: Check Trailer Brake Wiring – white text, no audible ding, the trailer disconnected icon is not lit
• TBD: Trailer Brake Disconnected – white text with red background, a single audible ding, trailer disconnected icon is lit (red trailer with slash through it in the upper right portion of the dash)

TLDR: A very intermittent short (less than half a second) may never trigger a message. If CTBW comes on, a short has existed for at least a second. If you get a CTBW/TBD cycle every 5 seconds, it’s been shorted all that time. This will stop as soon as the short is resolved. A continuous TBD is an open circuit.

I started testing with load resistors (6 Ohm 50W) that simulated trailer brakes. With 2-6 ohms, the truck would detect a trailer connected. But when I got down to 1.5 ohms, the CTBW/TBD cycle of errors would begin. So would a dead short.

If a short or high current on the brakes is detected, after 1 second you will see CTBW. If the problem goes away during that time, the message will go away. If the condition exists for another 5 seconds, it goes to TBD. If the problem goes away at this point, this will clear also. But if the condition persists, it will cycle between CTBW and TBD every 5 seconds.

While a short or high current scenario is detected, THE BRAKE CONTROLLER WILL NOT OUTPUT A BRAKE SIGNAL. If the short condition is resolved while already braking, the brakes will come on (I experienced this once – when stopping, there were no trailer brakes to start so I got into the truck brake, then the trailer brakes kicked in and scared the crap out of me). If you are braking when a short is detected, it will continue to brake assuming the short isn't bad enough. But as soon as the brakes are released the short will be detected, and the output disabled.

In contrast, an open connection to the trailer brakes will delay for one second, then you will see TBD. The red no trailer icon will persist as long as the brake wiring shows an open circuit.

Trailer Troubleshooting​

From there I connected the truck to the trailer again, and (luckily) it cycled CTBW/TBD. I cut the brake wiring and only connected the brakes on the front axle of the trailer, and the error went away. The back axle brakes by themselves caused the error. When splitting the back axle in to left/right, the short disappeared entirely, so I suspect the issue is in one of the wires. I’ll be re-wiring the trailer brakes soon to remedy the issue.

Etrailer has some good articles on expected current (amps) and resistance (ohms) for different trailer configurations. That’s a good place to start to troubleshoot the trailer wiring. I won’t rehash that here.

Truck Troubleshooting​

(I didn’t go this far, but this was my plan)
If the trailer had checked out, I was planning to connect a load resistor (6 ohms 50W will do it – just be aware it will get hot when braking) across the ground/brake pins of the connector on the truck and drive around with my “virtual” trailer. If there had been a short or break in the truck wiring, my thought was that it would show up and not have all of the complications of a real trailer to troubleshoot. It would have made troubleshooting with the dealer easier.

Technical Details​

I put a oscilloscope on the trailer wiring so see what it was really doing.
The brake controller uses PWM (pulse width modulation). With no trailer connected, it sends out a 12V DC 1ms pulse 3 times a second. When the trailer is connected this voltage will drop a little but this “sensing” pulse continues to check if the trailer is connected. I can actually hear this in my brakes – there is a slight ticking noise coming from the trailer brakes 3 times a second. When you brake, a 250Hz 12V DC PWM signal comes out, with the duty cycle proportional to your braking, as well as gain and trailer settings. The PWM sensing pulse is there all the time even if there is not a trailer connected. Even with an open circuit, the brake controller will still output a full signal when braking. But if it gets shorted or the braking current (amps) is too high, it will shut off. It still senses 3 times a second when shorted and if the short is resolved, it will begin to output again. I would assume the one second delay earlier is three tries before it gets disabled.

Edit: Be sure to see Part 2 below: https://hdrams.com/forum/index.php?...roubleshooting-technical-info.6004/post-96765

 

[Brutal_HO]

This post is about the brake controller on the 2021 HD Ram. First, my story. Second some reverse engineering and description of the warnings on the dash. Finally, some technical details. I would assume this information would apply to other years in the same generation of truck, but outside of that, I don’t know.

I was greeted with Check Trailer Brake Wiring/Trailer Brake Disconnected on our first trip out with our 2021 2500 and travel trailer combo. The same trailer on our 2018 1500 had no issues earlier in the year. At first it happened after a few hours. Sometimes it would just say Check Trailer Brake Wiring, and other times it would ding and say Trailer Brake Disconnected. I read this related post: Trailer Brake Disconnected. I found I had the “old” style 7 pin connector, and I needed to extend mine anyway – so I ordered a Hopkins HM20048 and put that on. The first time I plugged it in, I had no brakes and no left turn signal on the trailer. I bent the pins a little and got them working. Unfortunately, after a short while on the next trip, the error returned.

What bothered me is the error wasn’t real helpful. I wasn’t sure if I had a short, break, or something intermittent. Nor did I know if the problem was in the truck or trailer. I went about troubleshooting and here is what I learned.

Brake Controller Operation​

In the rest of this post, I will refer to the two warning messages and accompanying indicators/audibles as CTBW and TBD.

• CTBW: Check Trailer Brake Wiring – white text, no audible ding, the trailer disconnected icon is not lit
• TBD: Trailer Brake Disconnected – white text with red background, a single audible ding, trailer disconnected icon is lit (red trailer with slash through it in the upper right portion of the dash)

TLDR: A very intermittent short (less than half a second) may never trigger a message. If CTBW comes on, a short has existed for at least a second. If you get a CTBW/TBD cycle every 5 seconds, it’s been shorted all that time. This will stop as soon as the short is resolved. A continuous TBD is an open circuit.

I started testing with load resistors (6 Ohm 50W) that simulated trailer brakes. With 2-6 ohms, the truck would detect a trailer connected. But when I got down to 1.5 ohms, the CTBW/TBD cycle of errors would begin. So would a dead short.

If a short or high current on the brakes is detected, after 1 second you will see CTBW. If the problem goes away during that time, the message will go away. If the condition exists for another 5 seconds, it goes to TBD. If the problem goes away at this point, this will clear also. But if the condition persists, it will cycle between CTBW and TBD every 5 seconds.

While a short or high current scenario is detected, THE BRAKE CONTROLLER WILL NOT OUTPUT A BRAKE SIGNAL. If the short condition is resolved while already braking, the brakes will come on (I experienced this once – when stopping, there were no trailer brakes to start so I got into the truck brake, then the trailer brakes kicked in and scared the crap out of me). If you are braking when a short is detected, it will continue to brake assuming the short isn't bad enough. But as soon as the brakes are released the short will be detected, and the output disabled.

In contrast, an open connection to the trailer brakes will delay for one second, then you will see TBD. The red no trailer icon will persist as long as the brake wiring shows an open circuit.

Trailer Troubleshooting​

From there I connected the truck to the trailer again, and (luckily) it cycled CTBW/TBD. I cut the brake wiring and only connected the brakes on the front axle of the trailer, and the error went away. The back axle brakes by themselves caused the error. When splitting the back axle in to left/right, the short disappeared entirely, so I suspect the issue is in one of the wires. I’ll be re-wiring the trailer brakes soon to remedy the issue.

Etrailer has some good articles on expected current (amps) and resistance (ohms) for different trailer configurations. That’s a good place to start to troubleshoot the trailer wiring. I won’t rehash that here.

Truck Troubleshooting​

(I didn’t go this far, but this was my plan)
If the trailer had checked out, I was planning to connect a load resistor (6 ohms 50W will do it – just be aware it will get hot when braking) across the ground/brake pins of the connector on the truck and drive around with my “virtual” trailer. If there had been a short or break in the truck wiring, my thought was that it would show up and not have all of the complications of a real trailer to troubleshoot. It would have made troubleshooting with the dealer easier.

Technical Details​

I put a oscilloscope on the trailer wiring so see what it was really doing.
The brake controller uses PWM (pulse width modulation). With no trailer connected, it sends out a 12V DC 1ms pulse 3 times a second. When the trailer is connected this voltage will drop a little but this “sensing” pulse continues to check if the trailer is connected. I can actually hear this in my brakes – there is a slight ticking noise coming from the trailer brakes 3 times a second. When you brake, a 250Hz 12V DC PWM signal comes out, with the duty cycle proportional to your braking, as well as gain and trailer settings. The PWM sensing pulse is there all the time even if there is not a trailer connected. Even with an open circuit, the brake controller will still output a full signal when braking. But if it gets shorted or the braking current (amps) is too high, it will shut off. It still senses 3 times a second when shorted and if the short is resolved, it will begin to output again. I would assume the one second delay earlier is three tries before it gets disabled.

Great writeup.

Assuming you did much of the static testing stationary? That seems to dispel the rumor that the brake power is reduced at low speeds, or was changed at some point? Did you measure the actual current as well?

 

[H3LZSN1P3R]

I have gotten this a few times with the molded plug on campers i have since just bent the pins drastically so it can be a pain to plug in but no more issues, this is after going through my old trailer and testing all the magnets and wiring

 

[Tom2531]

Assuming you did much of the static testing stationary? That seems to dispel the rumor that the brake power is reduced at low speeds, or was changed at some point? Did you measure the actual current as well?

All testing was done while not moving. The truck was "on", but not running. I did notice that the PWM signal never got to 100% duty cycle, even when I pulled the manual control all the way. I wasn't sure if that was related to the trailer profile (light electric) or not. It's possible that the PWM is reduced as a function of speed (especially at 0 mph) to limit current draw. Is the rumor just that as you slow down that the brake signal is reduced, given the same amount of brake applied? That would be tricky to test, but not impossible.

I did not measure the current going to the brakes from the brake controller. I only did that once with using the emergency brake switch just to get a baseline of actual current draw. I could measure current to the trailer but thats a little trickier.

 

[Brutal_HO]

I don't recall the specific details, and haven't really noticed any issue myself when setting brake levels around 25MPH. My controller will lock the wheels on 3.5-4.0 on my 12K fifth wheel set on heavy electric.

I've seen others say they measured lower voltage when stationary or below 30. I think in every case those were simple V-DC measurements done with a basic MM.

 

[Tom2531]

I've seen others say they measured lower voltage when stationary or below 30. I think in every case those were simple V-DC measurements done with a basic MM.

I can confirm that at 10MPH and above, 97% duty cycle on PWM is available - basically all the braking possible. From 10MPH to 0MPH it does lower the trailer brake max from 97% to 57%, linearly, as measured at the PWM output. This is on light electric with 10.0 gain. The other profiles may be a little different. The dash still says 100% whether using the manual override, or braking enough to get to 100% as indicated on the dash. So there is some truth to the rumor, but 10MPH seems to be the threshold. A lower gain also basically limits the max output. So the only way someone would see a full 12V is with a gain of 10.0, the truck moving faster than 10MPH, and with 100% braking as indicated on the dash.

I gathered some other data on the different profiles, so I hope to make that into something useful tonight.

 

[Brutal_HO]

I can confirm that at 10MPH and above, 97% duty cycle on PWM is available - basically all the braking possible. From 10MPH to 0MPH it does lower the trailer brake max from 97% to 57%, linearly, as measured at the PWM output. This is on light electric with 10.0 gain. The other profiles may be a little different. The dash still says 100% whether using the manual override, or braking enough to get to 100% as indicated on the dash. So there is some truth to the rumor, but 10MPH seems to be the threshold. A lower gain also basically limits the max output. So the only way someone would see a full 12V is with a gain of 10.0, the truck moving faster than 10MPH, and with 100% braking as indicated on the dash.

I gathered some other data on the different profiles, so I hope to make that into something useful tonight.

Awesome info, would make a great sticky.

 

[Tom2531]

Part 2:

I did some more tests. After gathering data with the scope, I tried to see what was available via OBDII. Luckily, you can query the PIDS on the ITBM (Integrated Trailer Brake Module). I have a OBDLink MX+ and I needed to use the FCA extended diagnostics add-on to get to them. This helped, as there is a PWM % PID and I could abandon the scope. I also found braking is in relation to the “Brake Pedal Status – Primary Circuit Pressure” in the ABS module. That combined with some manual readings, I was able to make the following observations.

All trailer modes will output 100% PWM above 10MPH with a gain of 10.0 when the dash indicates 100% brake. At speeds below 10MPH down to 0MPH, it gets reduced linearly to somewhere between 50% and 70% depending on the trailer type selected.

The manual lever doesn’t output PWM the same way the brake pedal does. 50% as indicated on the dash with the brake pedal uses the braking curves (a later chart) to determine what to output. The manual lever is proportional to the PWM output, taking into consideration the gain and vehicle speed.

It’s worth noting that the dash brake % isn’t the same for different trailer types. It’s pretty linear as compared to brake pressure, but there are some subtle differences between the trailer types. LE=Light Electric, HE=Heavy Electric, LEOH=Light Electric Over Hydraulic, HEOH=Heavy Electric Over Hydraulic.



800 inHg is what I could call “medium” brake pressure. 1500 inHg is what I could call “high” brake pressure. The braking curves below kind of follow these lines, but there are some nuances, so I generally ignore the dash percentage from here on and use inHg as my measured data for brake pressure. I posted this chart merely for reference.



The chart above shows the braking pressure vs the PWM output. The chart doesn’t go higher than 62% because the truck was stopped. That’s the whole 0-10MPH mentioned earlier. Let’s look at each trailer type. LE comes on slow at first, then goes up to the max with medium brake pressure. HE also comes on slow at first, but gets up to the max with a lighter brake pressure. LEOH stays on flat at about 4% PWM at first. Then it takes a high braking pressure to get to full output. HEOH comes on flat at about 8% PWM at first, and comes up to full output a little faster.

Lowering the gain has two effects. You can see this by looking at LE 10.0 and LE 5.0 in the chart. First, it delays the brakes coming on by increasing the pressure needed to first get them to activate. Second, it drops the maximum output down proportionally. A 5.0 gain will never output more than 50% PWM (above 10MPH). For hydraulic brakes at lower gains, they still have that low PWM when the brake is initially depressed – that doesn’t change. But the point at which it will ramp up is effectively delayed, as is the max output.

I wanted to know what this looked like while moving. Armed with the data logger, I came up with this chart:



The solid lines are the same LE and HE data from the previous chart done at 0MPH at 100 inHg intervals. The dashed lines are data recorded while moving above 10MPH. The data isn’t perfect because it would only poll at 500ms intervals, so I had to brake and accelerate at the same time over a 10-15 second period to get enough data. Generally, it looks scaled up as I would expect while moving, although HE seems a little more aggressive at first. Based on this, I would expect the braking curve to scale down between 10 and 0 MPH. It’s too hard to hold the truck at 5MPH and brake between 0 and 100% to determine if that is the case. I just wanted to do a test while moving and compare results.

Hopefully this helps someone, or at least you find it interesting.

 

[Brutal_HO]

Awesome report. Definitely makes me rethink using LE as the HE seems to come on too hard, too quick.

 

[ColoMan]

Great write up, thanks for doing this. I have the same issue with my 2021 with 5th wheel package. Trailer is 2021 and has no issues with my friends 2016 Ram only when hooked to mine. It’s very dangerous and intermittent, can go 300 miles no issues then no brakes for 10 minutes.

 

[BULLSANDBUCKSHUNTER]

My truck has same "disconnected" warnings and no brakes all the time. Lights on trailer stay on whole time so i know it aint, but that dam dinging and warning get annoying. Always happens first time on bumpy roads or off road and have to turn off truck to reset it once on smooth highway. Been playing with pins hopeful to help as one was clearly bent. I need to do some brake adjustment work on trailer side so aint stressed it yet. Thanks for great right up!

 

[Nd79]

I periodically wrap one layer of wire harness tape around my 7 pin trailer plug to keep it from jostling loose. My trailer gets pretty bumpy and I'll get the check trailer wiring message and I know it's time to re-wrap the trailer plug. One layer and it fits really snug, to the point its a pain to plug in for the first few times.

 

[Brutal_HO]

Does your trailer 7-pin have the right connector?

https://www.ramtrucks.com/BodyBuilder/service/Image?imageId=MtQrP%2FFqLY5r%2Fest8MtGjGgHzAHGUTU0WB3rWuqSY7YmQ2vEhuBWBBw100AuApmZ%0A

The old style is problematic and the first thing to check.

Old style:



New Style:

 

[fuchsroehre]

Took me a while to figure that out:
My 7k lbs intech trailer would never be able to lock the tires witch the hand slider fully engaged.
I had to drive with gain 10 to get a reasonable amount of brake force from the trailer but even then the empty trailer would not lock tires even when streets are wet.
My idea is that you set the gain to lock the tire at 100% hand lever actuation and then dial the gain back 1-2 points until it is not locking tires.
At gain 10 the truck trailer were very jerky, no fun to drive.
A loaded trailer always made me worry to crash into something due to poor brake performance.
Finally, after 6k miles and many trips with the trailer I tried to switch from light electric to heavy electric and that did the trick.
Brakes awesome now. Gain is at 2 empty and 3 loaded. Still a little jerky at times but that seems to be mostly at slow speeds around 10mph.

 

[steve49]

I'm glad I found this forum post! I just installed new self-adjusting brakes on my trailer and could faintly hear the ticking sound (PWM) as described above, thought I had screwed something up. Never heard it before with the old brakes, but it's not really noticeable till your down low near the wheels. Tom2531 thanks for the write up!

 

[b1lanc]

Thanks Tom2531 - Pulled our 5th Wheel for a first short trip last week - not happy with the brake gain settings yet and the trailer pads are probably not bedded completely. Set to HEOH and started with gain at 4.5 bumping it up to 5.5. Still felt like too much of a delay and then had to release pedal pressure once trailer brakes kicked in. Looking at some of the other RV forums, the RAM settings seem to be about 7.5-8.5 for Alliance as an example. I'm not sure I totally understand relationship between gain and pedal pressure but ideally, I'd like the response to be quicker and the pedal pressure to not change the trailer braking over time/speed which is what I experienced.

 

[BigRyanG]

Thanks very much @Tom2531 for all the effort and time in researching this and taking the time to put it all together here. Very helpful, and very interesting.

One query for you - would you think the Trailer detection for features such as trailer blind spot monitoring (and the additional length of the trailer) would also come from this trailer lights harness? As in it detects a specific resistance on the trailer lights plug and as such then triggers the "Blind Spot Alert with Trailer On" feature? or would this be triggered from some other signal?

My RAM 2500 is showing this alert even when no trailer is connected and trying to diagnose

 

[Brutal_HO]

Thanks very much @Tom2531 for all the effort and time in researching this and taking the time to put it all together here. Very helpful, and very interesting.

One query for you - would you think the Trailer detection for features such as trailer blind spot monitoring (and the additional length of the trailer) would also come from this trailer lights harness? As in it detects a specific resistance on the trailer lights plug and as such then triggers the "Blind Spot Alert with Trailer On" feature? or would this be triggered from some other signal?

My RAM 2500 is showing this alert even when no trailer is connected and trying to diagnose

OP hasn't logged on in about a year, maybe try sending a PM.

Now, as to the trailer BSM, it's simply plugging in the trailer (either 7-pin or 4-pin) that triggers this and the length is detected from the BSM radar in the taillight housing (or can be set to max). When I connect my 5th, I actually lie to it and select conventional. I get *some* extended BSM but due to the 5th wheel interfering with the BSM sensors, don't trust it completely.

I'd be looking at a short in your 7-pin or 4-pin wiring somewhere.

 

[BigRyanG]

OP hasn't logged on in about a year, maybe try sending a PM.

Now, as to the trailer BSM, it's simply plugging in the trailer (either 7-pin or 4-pin) that triggers this and the length is detected from the BSM radar in the taillight housing (or can be set to max). When I connect my 5th, I actually lie to it and select conventional. I get *some* extended BSM but due to the 5th wheel interfering with the BSM sensors, don't trust it completely.

I'd be looking at a short in your 7-pin or 4-pin wiring somewhere.

Legend - thanks for the quick reply. I figured it might be related. I have an aftermarket tray (or bed) and canopy fitted, so thinking its the wiring and how the lights have been picked up, perhaps off the trailer circuit. Will do some testing. Thanks again!

 

[UPSguy1994]

Legend - thanks for the quick reply. I figured it might be related. I have an aftermarket tray (or bed) and canopy fitted, so thinking its the wiring and how the lights have been picked up, perhaps off the trailer circuit. Will do some testing. Thanks again!

I had same issue but my truck was even turning on blind spot when I had no trailer even attached dealership found my trailer brake module was lock on the the on position haven't had the new one put in waiting for part but I will come back with updates.