trailer brake controller issues
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trailer brake controller issues
Hey guys new to the forum but needing some help. My 2004 5.4 f250 has a weird issue that I can not seem to pin point. The computer throws a p0720 and p0722 code but only when I put the truck in drive with a trailer with trailer brakes hooked up. With my foot on the break the speedometer will jump to about 15 mph and on my Scan tool the vss shows the truck is moving even when I'm just sitting in drive with my foot on the brake. If I unplug my trailer brake controller from under the dash all of the lights on the trailer work fine I just can seem to have a trailer brake controller hooked up. Ive tried the trailer on my fathers 2003 7.3 truck with the same controller with no issues. Its got me lost. I hate pulling a trailer without the brake controller hooked up.
Fleet Mechanic
Joined: Nov 2011
Posts: 1,825
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From: Land of Taxes
So the problem does NOT exist when the trailer is NOT connected to the truck, correct? If this is true it's likely the trailer inducing a fault...but read on...
http://www.ford-trucks.com/forums/15...t-working.html
Look at the post I just posted in the above link.^^^^^
What made you disconnect the alternator? Is the alternator charging the system properly, (13.8-14.2 VDC, running, at hot loaded idle)? Is the charge voltage low? If so a bad bridge diode can back feed AC power which can create electrical “noise” that can confuse electronic modules and digital communications. I don't ever recommend disconnecting the alternator while the engine is running. If the alt. is in question have it and the battery load tested.
Next step after verifying the alternator is good: Verify grounds...all of them.
You are likely missing a ground somewhere(an open ground circuit). Sounds like something could be seeking a ground through the path of least resistance. Could be either the truck or the trailer if the problem exists regardless of the trailer being hooked up or not.
If both truck and trailer are rusty then both are suspect. On the truck start with all the grounds you can find especially the main starting circuit negative connections all the way down to the starter + connections. Then work your way back from this secondary system( the large battery wires) to the primary ground wires (the smaller 12gauge wires seen throughout the truck).
Try hooking a clean temporary ground between the truck frame and the trailer frame.
You could try pulling the fuses one by one until the problem stops. This will help zero in on which circuit is the problem.
http://www.ford-trucks.com/forums/15...t-working.html
Look at the post I just posted in the above link.^^^^^
What made you disconnect the alternator? Is the alternator charging the system properly, (13.8-14.2 VDC, running, at hot loaded idle)? Is the charge voltage low? If so a bad bridge diode can back feed AC power which can create electrical “noise” that can confuse electronic modules and digital communications. I don't ever recommend disconnecting the alternator while the engine is running. If the alt. is in question have it and the battery load tested.
Next step after verifying the alternator is good: Verify grounds...all of them.
You are likely missing a ground somewhere(an open ground circuit). Sounds like something could be seeking a ground through the path of least resistance. Could be either the truck or the trailer if the problem exists regardless of the trailer being hooked up or not.
If both truck and trailer are rusty then both are suspect. On the truck start with all the grounds you can find especially the main starting circuit negative connections all the way down to the starter + connections. Then work your way back from this secondary system( the large battery wires) to the primary ground wires (the smaller 12gauge wires seen throughout the truck).
Try hooking a clean temporary ground between the truck frame and the trailer frame.
You could try pulling the fuses one by one until the problem stops. This will help zero in on which circuit is the problem.
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DGMFORD
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Sep 30, 2020 08:59 PM
