Check Engine Light Comes On When Tekonsha P3 Brake Controller is Plugged In But Goes Away When Not

Question:

I just installed a tekonosha p3 on my 15 Ford F-150 and it’s throwing me a check engine light now and i tried to unplug it to see if that fixed it and it’s still throwing me a check engine light what could be causing this

asked by: Dillon W

Expert Reply:

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 Ford), 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). If that doesn't work you need to go to an auto store and get the code run and we can go from there.

expert reply by: Noah E