"Trailer Wiring Fault" & "Trailer Disconnect"

[stonefly]

I've had a long-standing problem with my travel trailer. I've reviewed many of the threads related to gain insight messages "Trailer Wiring Fault" & "Trailer Disconnect". I'm hoping for some insight from anyone who knows more about F-150s than do I (that should cover just about anyone on the forum).
Below is a summary of the phenomenon.
Additionally see screenshot from Forscan Lite indicating Trailer Brake output "short to ground". Cannot seem to find the date of occurrence anywhere, but highly likely AFTER it was evaluated by local dealer.

		Notes & Questions
Problem:	Message: "Trailer Wiring Fault" upon connection to trailer	Occurs with 7-pin connection on Travel Trailer. No message when connecting 4-pin connector on boat;
Light check		All lights functional
Depress Brake Gain tabs	Message: "Trailer disconnected"	Message received during each trailer use over 1 year; vehicle light check indicated all functional, BRAKES FUNCTIONAL when towing; Trailer D/C is now constant when BC gain activated. TRAILER BRAKES NON-FUNCTIONAL when driving
		Suggests fault in brake controller function
FUSES Checked	42 - Trailer Brake Module	# 42 Continuity Functional; NONE of the fuses were fully seated
Test GND Resistance	Truck power OFF, No Trailer
GND - Frame	0.0 ohms	Just what I'd expect
GND - 12V	328 k ohm	Why do I see these resistance values for 4 pins? Should I not expect to see 'O.L' for all?
GND - BC Output	81 k ohm
GND - R TURN	76 k ohm
GND - L TURN	76 k ohm
GND - Reverse	'O.L'
GND - TAIL/Run	'O.L'
Test Pin Voltage	Truck power ON, No Trailer
GND - 12V	13.3 Volts
GND - TAIL/Run	12.99 Volts
GND - R TURN	100 mV	signals not activated; values expected, no variation in measurment
GND - L TURN	100 mV
GND - BC Output	100 - 350 mV	brakes not activated; constant variance within noted range
	Brake Pedal depressed
GND - BC Output	6.5 Volts	Should I not expect 12 Volts for BOTH?
Test Pin Voltage	Brake Gain adjustment activated
GND - BC Output	8.5 Volts
Other
	Pins on truck and trailer and their general fit	Cleaning THOROUGHLY changed nothing; no intermittent connections noted; assessed multiple times over past year
Uninstall/Reinstall Trailer Profiles	Ineffective
Ford Dealer Assessment	Simulator	all the little lights come on when they are supposed to…

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[chrisO2002]

I also have done a pretty extensive review of the four different forums on this topic. The only "fixes" that I have seen so far is one person had the 7 pin connector replaced and one person rewired their right side rear break light. EVERYONE is searching for answers...

 

[My 2ND Ford]

I've had a long-standing problem with my travel trailer. I've reviewed many of the threads related to gain insight messages "Trailer Wiring Fault" & "Trailer Disconnect". I'm hoping for some insight from anyone who knows more about F-150s than do I (that should cover just about anyone on the forum).
Below is a summary of the phenomenon.
Additionally see screenshot from Forscan Lite indicating Trailer Brake output "short to ground". Cannot seem to find the date of occurrence anywhere, but highly likely AFTER it was evaluated by local dealer.

		Notes & Questions
Problem:	Message: "Trailer Wiring Fault" upon connection to trailer	Occurs with 7-pin connection on Travel Trailer. No message when connecting 4-pin connector on boat;
Light check		All lights functional
Depress Brake Gain tabs	Message: "Trailer disconnected"	Message received during each trailer use over 1 year; vehicle light check indicated all functional, BRAKES FUNCTIONAL when towing; Trailer D/C is now constant when BC gain activated. TRAILER BRAKES NON-FUNCTIONAL when driving
		Suggests fault in brake controller function
FUSES Checked	42 - Trailer Brake Module	# 42 Continuity Functional; NONE of the fuses were fully seated
Test GND Resistance	Truck power OFF, No Trailer
GND - Frame	0.0 ohms	Just what I'd expect
GND - 12V	328 k ohm	Why do I see these resistance values for 4 pins? Should I not expect to see 'O.L' for all?
GND - BC Output	81 k ohm
GND - R TURN	76 k ohm
GND - L TURN	76 k ohm
GND - Reverse	'O.L'
GND - TAIL/Run	'O.L'
Test Pin Voltage	Truck power ON, No Trailer
GND - 12V	13.3 Volts
GND - TAIL/Run	12.99 Volts
GND - R TURN	100 mV	signals not activated; values expected, no variation in measurment
GND - L TURN	100 mV
GND - BC Output	100 - 350 mV	brakes not activated; constant variance within noted range
	Brake Pedal depressed
GND - BC Output	6.5 Volts	Should I not expect 12 Volts for BOTH?
Test Pin Voltage	Brake Gain adjustment activated
GND - BC Output	8.5 Volts
Other
	Pins on truck and trailer and their general fit	Cleaning THOROUGHLY changed nothing; no intermittent connections noted; assessed multiple times over past year
Uninstall/Reinstall Trailer Profiles	Ineffective
Ford Dealer Assessment	Simulator	all the little lights come on when they are supposed to…

Is your fault intermittent? Have you noticed that the fault occurs only when you turn a certain direction? I ask because this because when my brother in law and me were trailering north to go snowmobiling we were getting an intermittent message when we would turn a corner, can't remember which way, that the trailer was disconnected . We finally determined that the plug was partially pulling out . We solved it temporarily by using a bungee to secure it into place. It was the trailer plug that was worn and not fitting tightly. Hope this helps.

 

[stonefly]

I have not observed that it occurs AFTER getting underway; occurs immediately following connection.
The new thing is that in addition to "trailer wiring fault" (upon connection) I see "trailer disconnected" when pressing the BC tabs. "TWF" with functional brakes was the behavior until recently.


I will be taking my truck back to dealer tomorrow with the data gathered so as to get them focused on a potential solution.
The service tech notes from first visit indicated no related DTCs and that without assessing my trailer as well there was no means of diagnosing the fault... No way possible to get my trailer into their service area, also ignoring that there are expected outputs that can be evaluated to determine fault location.
Second visit (next day, due to dissatisfaction with another issue) shop foreman used a simulator and the lights come on as they should.
Given the low voltage when brake pedal and BC tabs are activated, it suggests the simulator is an insufficient diagnostic tool.
Given the B148A: 11-08 code I'll suggest they replace the connector.

I'll post more about any corrections. Your help is appreciated...

 

[stonefly]

Posting updated data to make the best case when I take truck back to dealer tomorrow.
GIven it was not clear if the fault was truck v. trailer, I had to start writing down my own diagnostic approach.
Happy reading; will post results soon that may help everyone.

VIN: 1FTFW1ED8NFA16722
		Notes & Questions
Problem:	Message: "Trailer Wiring Fault" upon connection to trailer	Occurs with 7-pin connection on Travel Trailer. No message when connecting 4-pin connector on boat;
Vehicle Light check		All stop/turn/reverse lights functional
Depress Brake Gain tabs	Message: "Trailer disconnected"	Message received during each trailer use over 1 year; vehicle light check indicated all functional, BRAKES FUNCTIONAL when towing; Trailer D/C is now constant when BC gain activated. TRAILER BRAKES NON-FUNCTIONAL when driving
Suggests fault in brake controller function
Cleaning/Fitment	Spray electronics cleaner on male/female aspects followed by deep insertion cleaning with thin blade/cloth and light spray with CorrosionX protectant.	Cleaning truck and trailer connectors THOROUGHLY on multiple occasions changed nothing; no intermittent connections noted over course of 1 year. TWF ALWAYS occurred upon trailer connection. Cleaning connectors and manipulating connection NEVER corrected the TWF message even temporarily.
Uninstall/Reinstall Trailer Profiles	Ineffective
Ford Dealer Assessment 1	No related DTC; DTC log cleared. Simulator	All the little lights come on when they are supposed to… What is the voltage threshold for the lights to turn on? If < 6.5 Volts, simulator is insufficient diagnostic tool.
FUSES Checked	42 - Trailer Brake Module	# 42 Continuity Functional; NONE of the fuses were fully seated. Removal/reseating fuses reportedly has cleared message "Trailer Brake Module… faults. No apparent faults from DTC
Test GND Resistance	Truck power OFF, No Trailer
GND - Frame	0.0 ohms	Just what I'd expect
GND - 12V	328 k ohm	Why do I see these resistance values for 4 pins? Should I not expect to see O.L for all?
GND - BC Output	81 k ohm
GND - R TURN	76 k ohm
GND - L TURN	76 k ohm
GND - Reverse	'O.L"
GND - TAIL/Run	'O.L"
Test Pin Voltage	Truck power ON, No Trailer
GND - 12V	13.3 V
GND - TAIL/Run	12.99 V
GND - R TURN	100 mV	Turn signals not activated; values not unexpected but less-than-ideal, no variation in measurement
GND - L TURN	100 mV
GND - BC Output	100 - 350 mV	Brakes pedal not depressed; continuous variance within noted range; can be reasonably interpreted as shorting to GND consistent with B148A:11-08 Circuit Short to GND noted in Forscan error log (occurred AFTER simulator assessment noted above)
	Brake Pedal depressed	Expected Value = 12 Volts
GND - BC Output	6.5 Volts
	Brake Gain adjustment activated
GND - BC Output	8.5 Volts
Other
Ford Dealer Assessment 2	Pending; Provided relevant Forscan log screenshots to Eddie Ruiz	B148A:11-08 Circuit Short to GND; "Miles since DTCs cleared = 57" Trailer has not been connected to truck in several thousand miles, thus trailer did not cause the logged fault
		Preventive replacement of fuse 42 diagnose location of short and replace appropriate components

 

[uk_brewer]

Have you had any success getting this diagnosed yet? I’m taking mine in for the same issue on Monday.
I get the same “trailer disconnected” error message when first connected. I can see the side marker lights are still on, my rear view camera is still functional. Will slow down and test trailer brakes manually and Those are still operational.

 

[stonefly]

The dealer replaced the connector, P/N HU5Z-14489-B "SLEEVE-WIRIN" [truncated on svc record]
Service advisor thanked me for diagnosing the fault on their behalf.

I am concluding that the lowly service tech doing the job relies heavily on TSB, SSM and WSM for actions to be taken. Recorded notes suggest restricted thinking. I would imagine that rather than ask the question "what would have to be true for this reported event to occur?" the tech simply followed the path, so to speak and since no DTC, no problem existed and couldn't be diagnosed without the trailer attached...
Not to mention the half-dozen other cars he's being asked to fix simultaneously...
My opinion is the tech should have measured resistance and voltage as I did on the first visit. I would imagine the high-resistance connection with the POWER OFF would have suggested a fault if they were thinking out-of-the-box.

Interestingly, there was also a fault in the trailer wiring (which the truck appears to have detected [Trailer Wiring Fault], but the waters were muddied by the truck fault).

Pulling the breakaway pin out, the brake wires smoked due to dead short. Short caused by the undercover panel screwed through into the wiring harness; cover has not been removed previously. Took it a year to fully short out, apparently causing the "Trailer Disconnected" message. $1200 repair.
Getting trailer back today and leaving on a 25-day trip Monday. I will post more if anything noteworthy appears.

 

[uk_brewer]

Looks like they replaced the trailer tow wiring harness. I’ll be sure to let the service department know.
Thanks.

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