Andy Thomson has been writing for RV Lifestyle Magazine for more than 25 years. He also owns and operates Can-Am RV Centre located in London, ON.

Every week visitors to the store come in with towing stability concerns that they need correcting. When we road test their rigs, 90 per cent also have a problem with how their brake control has been configured or with the brake control itself.


Electric brakes on the trailer produce more stopping force as the voltage applied to them is increased. By modulating the voltage, you can synchronize the trailer brake force with the tow vehicle. Modulating the voltage is the function of the brake control.


Unfortunately, the most popular brake controls sold are “timer controls”. The way these controls operate is that they start to gradually increase voltage when the brake lights are activated. The longer you hold pressure on your brake pedal, the longer the brake lights remain on and the higher the power output becomes to the trailer brakes. The problem with this system is that in a panic stop you do not want the brakes to come on gradually, you want them full on right now! At the other end of the spectrum, during a long gradual stop the trailer brakes will be on to their maximum setting part way through the stop. This can overheat the trailer brakes causing excessive wear and glazed brake linings on the trailer.


If you suspect you have a timer control, but you are not sure, it is usually simple to tell. Most timer controls have two adjustment knobs or sliding scales. One is the “Gain Setting” that establishes the maximum voltage to the trailer brakes, the other sets how quickly the voltage increases. The display on these controls will read a maximum of 12-13 if it is measuring voltage or 99 if it displays percentage. To test what type you have, turn or slide the “Gain Setting” to maximum. While sitting still with the trailer connected, if the control gradually counts up to its maximum value you have a timer control.


In my opinion, these brake controls should not be used on the highway. Not only are they much less safe and uncomfortable to use, but they also result in excessive brake wear which will be far more costly than the price of a good brake control.


Better brake controls use an accelerometer or inertia sensor to determine how hard the trailer brakes should be applied. However, if these controls are not adjusted properly, they will not work much better than the timer controls. The instructions for these controls don’t make a great deal of sense – it is as if they were written by someone who was worried that too much trailer braking could cause loss of control. We have learned on the test track that you can lock up the trailer brakes many times on different surfaces and it simply never causes an issue. I have done a great deal of towing on ice and snow and I often use the trailer brakes alone for additional control. Even on snow, the trailer won’t lose directional stability with the brakes locked up. Our goal then with the brake control setting is to have maximum braking in a panic stop, but smooth and balanced braking the rest of the time.

The most popular inertia control is a Tekonsha P2. Most other inertia controls have similar controls and function in a similar way. Let’s go over how to adjust the Tekonsha P2, and you can translate the method to another brand.


Brake Control Adjustment


On the P2 control there is a button, a knob, a lever and a display.

1) The Boost button is on the top right corner

2) The Gain Control knob is on the top left

3) The Manual Actuation Lever is on the bottom

4) The Display Screen is in the centre


1) The “Gain Control Knob” is the most critical adjustment. It provides maximum braking when it is pushed all the way forward and no braking at all when rolled all the way back.


Roll the Gain Control Knob all the way forward for maximum braking, then pull the manual lever on the bottom all the way over. The display will read the output voltage to the trailer brakes, between 12 and 14 Volts. This is the power you want going to your trailer brakes in an emergency stop.


If you roll the knob back just one swipe you will notice that the voltage drops off dramatically. 95% of trailers can be operated with the gain control in the full “on” position. So, to start with, leave the gain control full on.


2) The “boost control” button can be confusing. The boost button is used to augment braking with a surge of power as the stoplights come on. Kind of like the timer control, but it is a pre-set not an increasing amount. So, on position B_ the only part of the control supplying brake voltage is the accelerometer. On B1 about 2 volts are directed to the trailer brakes as soon as the lights come on and the accelerometer power is added to it. B2 about 4 volts and B3 about 5.5.


Pushing it repeatedly cycles between four positions B, B1, B2, and B3. A few seconds after selecting one of the four options, the screen reverts back to reading “c” so the only way to know which boost level you are set to, is to cycle through the settings again. Start on position “B_”

3) The “Manual Actuation Lever” allows you to apply the trailer brakes without using the vehicle brakes. The further you pull it across, the harder the trailer brakes are applied.


4) The Display will read “c” when you are towing, which stands for “connected”. This means the control sees a connection to the ground, likely through the brake magnets. If the display shows “NC” it means the trailer is not connected. If you see this stop as soon as it is safe to do so and correct the problem, usually the plug has loosened or come out of the hookup.


Now you are ready to head down the road and check the control settings. To start, we set the control to maximum gain and zero boost. As you start moving, pull the manual actuation lever over and confirm that you have working trailer brakes. Next, on a quiet road, try braking firmly from about 60 MPH. You should feel the trailer brakes help to stop the car slightly. About 80% of combinations work very well at this setting.


If you get the sensation that the trailer is pushing on the car, then adjust the Boost switch to “B1” and try again, it is rare to need “B2” but not a problem if that is what it takes. Needing “B3” is very rare.


Often, a new trailer will need B1 or 2 but after towing for a few hundred kilometres the brakes will become too aggressive. Don’t turn the gain knob down, instead lower the boost setting.


Starting from the position with full gain and the boost on b_ you find the trailer brakes are too aggressive. Then you need to back off the gain adjustment slightly – you can do this while holding the brake lever on the bottom over, so you can see what voltage you are adjusting to. Try backing off to 11 volts and see how the braking performs, it is rare to need to go below 10 volts.


You may find that the setting that gives you good braking at highway speed becomes a little aggressive at low speeds. This is normal, as the control does not know how fast you are going. To make a smoother stop, try letting up on the brake pedal most of the way when you are at about 40-50 KPH, this will reduce the deceleration, and the trailer brakes should back off and give you a smoother stop.


Have your brake control settings mysteriously changed? What we have found is that parking lot attendants, oil change mechanics, etc. love to play with that box under the dash. So, they might push the boost or wind the gain control, but they don’t know what they did, so they can’t put it back to the original settings, even if they were inclined to make an attempt to do this.


The mistake we see on many brake control units is that people have it set on B2 or B3, but have the gain turned way down, so the brakes feel OK in an average stop, but the most power they will ever send to the brakes is about 5 volts, so they have no extra braking in a panic stop.


I have one little trick that I do with the Boost button if I am driving in snow – I set it for B2 and then if I want just the trailer brakes on for additional control, I can just touch the brake pedal enough to activate the brake lights. This does not apply the car brakes, but it puts the trailer brakes on to keep you in a straight line, and it is easier than taking your hand off the wheel to manually apply the control. (If you have a diesel with an exhaust brake, you can just turn the exhaust brake off in ice or snow.)


Another reason your brake control may need changing is that as trailer brakes work in, they become more aggressive. If you find they become even more aggressive at low speed but no stronger at high speeds, then the trailer brakes themselves may need adjusting. The self-adjusting brakes on some trailers sometimes need one manual adjustment to get them started, and then they are usually fine after that.


The third type of brake control is the vehicle sensing variety. This plugs into the data port under your dash. These brake controls have the advantage of knowing how fast you are going, so they are smoother at low speeds. Built-in factory controls on new trucks often use these systems.


Brakes are very important – so never hesitate to call with any questions about your controls and settings!

Read Andy’s last column here.

For a full archive of Hitch Hints, click here.

Andy Thomson owns and operates Can-Am RV Centre in London, Ontario.

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