Tekonsha Prodigy P3 Trailer Brake Controller - Issue noted after installation

klenger

This may sound somewhat like a broken record (if you remember what a record is), but after the issues I noted in the thread labeled "Tekonsha Prodigy RF Wireless Trailer Brake Controller - Issue noted when towing" I decided to remove the RF wireless brake controller and install a Tekonsha Prodigy P3 hard-wired brake controller.  I order the P3 and Jeep adapter cable P/N 3014-P from Amazon and installed the system with no serious problems.  

Before I ever got around to connecting the T@B to my tow vehicle and testing the P3, I was driving my Jeep around town (without the T@B) and operated the manual brake control lever on the P3.  To my amazement, I immediately got a CHECK ENGINE LIGHT and another light on the dash.  It turns out the light was a traction control failure light, which triggered the CHECK ENGINE LIGHT.  Shutting down the tow vehicle cleared the lights, but they would reappear anytime I activated the manual brake control lever AND with the transmission in gear (stationary or moving).  I had a pretty good idea what the issue was, but spent the evening googling the interweb looking for answers.  I did find a few hits, the most helpful on a Toyota website describing a similar issue.  

Here's an explanation and cause of the problem:

When the brake controller manual lever is activated, a switch or relay is activated in the brake controller that connects +12 VDC battery power to the tow vehicle brake light circuit. This activates the tow vehicle and trailer brake lights for safety proposes.  In newer vehicles, with many attached computerized systems (traction control in the case of the Jeep), the tow vehicle's computer may sense this un-commanded brake light activation as a system failure and illuminate the CHECK ENGINE LIGHT, and possibly disable the affected systems. By adding the diode in the brake light circuit (polarity is important), the brake light signal is prevented from back-feeding into the tow vehicle's electrical system and therefore, avoids the CHECK ENGINE LIGHT faults.  NOTE Current flows from anode to cathode in a conventional junction diode, but not in the reverse direction from cathode to anode (one way).  See attached picture for more information.

I believe this issue could be "fixed" by Tekonsha by adding a programmable setting to the controller to disable the brake signal back-feed to the tow vehicle for newer vehicles that have issues like this, but it seems that once a manufacture brings a product like this to the market, they just don't go back and make design changes. 

Note for Jeep Wrangler JL owners: If you are looking for a brake control adapter cable for your vehicle, the Tekonsha 4105-P IS the correct part for the Jeep JL, even though it is only marked for the Jeep Cherokee.  Simply add an inline diode as shown in the drawing below.   I hope this helps anyone who has had this issue and wondered how to fix it.  I suspect that this issue will occur with most any brake control system that has the manual activation lever or button. 

tabiphile

Or....don't play with the brake controller when you aren't towing? I usually disconnect and remove my P3 from the TV when I'm not travelling and towing.

klenger

^^ The same issue happens when I was towing.  I just happened to notice it the first time while not towing.

BrianZ

Great discovery & fix, @klenger!
So, does this mean your original issue was not due to the wireless device?  And could the diode fix be used in the wireless system?

klenger

No, two entirely different problems.  This issue is totally fixed by the addition of the diode and the P3 seems to work great, but I've only towed locally with it so far.   Also note that this issue is only relevant to some newer vehicles which see the uncommanded (brake pedal not pressed) brake light signal as a fault. 

JEB

klenger said:

No, two entirely different problems.  This issue is totally fixed by the addition of the diode and the P3 seems to work great, but I've only towed locally with it so far.   Also note that this issue is only relevant to some newer vehicles which see the uncommanded (brake pedal not pressed) brake light signal as a fault. 

I have not seen this issue with my brake controller.  I have a Jeep as well.  Did you by chance hook an OBD II scanner up to see specifically which fault code was triggering the check engine light?  I'd be curious to see if the brake controller was causative or the CEL was coincidence.

klenger

The CEL is triggered by the traction control light being illuminated by the brake light circuit from the brake controller.  I could reproduce the incident every time.  Note my Wrangler is a 2019 JL model which may be quite different than the older Jeep models.

JEB

klenger said:

The CEL is triggered by the traction control light being illuminated by the brake light circuit from the brake controller.  I could reproduce the incident every time.  Note my Wrangler is a 2019 JL model which may be quite different than the older Jeep models.

I know what you said but an OBDII scanner would identify the exact fault code and store the event.  Did you scan?

klenger

I did not.  

JEB

That’s too bad.  I know a lot of people who tow with Jeeps and I have never heard of a brake controller throwing a fault code.  But it is interesting. I’d be curious to know specifically what system the brake controller is fooling.  Triggering the traction control would not normally cause a fault code.  Otherwise, you’d light the CEL every time you hit a slick spot. 

Michigan_Mike

I received a “trailer wiring disconnected” message and audible bell sound on my 2016 Silverado whenever I’d hit a bump or occasionally on turns (vehicle has the towing package) while towing my former T@B 320.  I had to go through and check all the connections and grounds in the 320 and during this process the problem eventually went away.  

These anomalies are annoying and very frustrating for sure.  I never experienced any issues with the Tekonsha wireless controller and enjoyed owning and using it for the time I had it.  You would think that the manufacturer would address the issues experienced by others (as noted) and further enhance and develop their product, but sometimes this process requires contacting the manufacturers tech department (if possible) and discussing the issue and creating an awareness.