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Discussion Starter · #1 ·
We ordered our Acadia with the trailer package. All of the lights on the trailer worked, but I found that when I put the vehicle in reverse the trailer brakes locked up. The trailer has surge brakes, and when the vehicle is place in reverse it should de-activate the brakes on the trailer so it can back-up.

I took the Acadia to a trailer shop, and they checked the wiring and the fuses. They found that the center connector, which is for reverse, had no power. They check the fuses and they were all ok. They advised me to take it to the dealer for repairs.

I took the Acadia to the GMC dealership on Monday. They check everything and and discovered the same thing as the trailer shop. They were not sure what was causing this problem. They Called GM engineering and they didn't know what would cause this problem. GM advised the dealership to replace a some sort of relay module.

They got the part today and installed it. No luck..It's still not working. They called the engineers again and they didn't know how to fix it. The dealership called me tonight to pick up the vehicle and explained that they dont have a fix for it. They also told me that they tested all of the other Acadias on the lot and all of them had the same problem. They had the Acadia for 3 days and they don't know how to fix this wiring problem..I'm mad...I've only had it for 2 week and already in the shop..Not good GMC!!!

Why would GMC install a tow package and not test the wiring???? not a good move...It looks like another recall..
 

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Well, it's not that it wasn't tested and working, it's very likely that in the swtichover to actual buildable units an error arised in the form of either an assembly issue or more likely a defective part from a supplier that's the culprit--just not immediately noticed in build.

That said, if it really is a common thing, it likely will be another recall, but we'll see. Sounds very much like an electronic sensor malfunction of some kind, though one would think the GM engineers that designed it would be able to figure it out pretty quickly...or not.
 

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This isn't news I want to hear. I'm currently on the hunt to purchase a camper that I will need for a trip in July. I don't want to have to deal with trailer wiring issues! *ack* Keep us posted on whether you receive a fix for it or not. Thanks!
 

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Web Raven said:
This isn't news I want to hear. I'm currently on the hunt to purchase a camper that I will need for a trip in July. I don't want to have to deal with trailer wiring issues! *ack* Keep us posted on whether you receive a fix for it or not. Thanks!
Is this only a problem if your trailer has trailer brakes? I tow, but none of the trailers I tow have brakes on them. Does this issue affect the lights in any way?
 

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pete7919 said:
Web Raven said:
This isn't news I want to hear. I'm currently on the hunt to purchase a camper that I will need for a trip in July. I don't want to have to deal with trailer wiring issues! *ack* Keep us posted on whether you receive a fix for it or not. Thanks!
Is this only a problem if your trailer has trailer brakes? I tow, but none of the trailers I tow have brakes on them. Does this issue affect the lights in any way?
From the original poster, it sounds like the lights were all working properly, there was just an issue with the surge brakes on the trailer when backing up.

This obviously won't affect me if I get a camper that doesn't have brakes. *fingers crossed* :)
 

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"With surge brakes, braking is automatic and requires no electrical connection between the tow vehicle and trailer (except for the lights). The surge coupler is mounted on the tongue of the trailer. Inside is a linkage connected to a hydraulic master cylinder. When the tow vehicle applies its brakes, the forward momentum of the trailer pushes on the surge coupler, causing it to slide rearward and apply pressure against the master cylinder piston rod."

Am I under the impression it is a trailer issue not a tow vehicle issue because the lights work fine?
 

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There are newer versions using electronics to engage trailer braking these are being used in campers and higher end trailers, by the look of the boat in the picture I would assume that it has the newer electronic braking system. The older surge brakes did not require any electronics to operate as debates has explained.
 

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Surge brakes have an electrical bypass feature for reverse.....so when you back up, they are deactived. Otherwise, the same force that causes the brakes to activate when moving forward (the trailer pushing on the tow vehicle) will lock up the trailer brakes when pushing the trailer in reverse. I dont have a trailer with these, so I'm not sure how they are wired exactly....I would think its hooked to the reverse lights on the tow vehicle.

Also, most trailers of this type have a pin that can be inserted in the tongue to manually deactivate the brakes for backing up.
 

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On my boat, backing down a ramp, no problem. Backing uphill, like to the garage, surge brakes kick in. I just take the safety chain hooks, stick them in the gap the surge mechanism works in, back uphill with no problems. This could be a temporary fix for your Acadia, I would definitely raise heck until the dealer or GM fixed the problem.
 

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Discussion Starter · #10 ·
The trailer was tested and the problem was found to be with the Acadia. I thought it was interesting that when the dealership test the other Acadias on the lot with the tow package ...they found that none of them were working...This was not the same dealership where I purchased the vehicle. I called the dealership where I purchased the Acadia and they are going to test their vehicles today. I'm also callin GM on this for some sort of answer..
 

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I'd have to agree that it sounds like a trailer problem to me. My experience with surge brakes is that they are a purely mechanical system, the only wiring is for lighting (4 pin flat). The 7 lug connector that comes on the car is not completely active if you do not have an aftermarket brake controller mounted inside the car. That is what the extra wire that came in the glove box is for- you hook up a device (not included with the car) to control the electrical trailer brakes. Without the controller, I wouldn't expect there to be a brake signal at the 7 lug connector. What kind of connector is on the trailer now- 4 pin flat, 7 lug round, something else?
 

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Discussion Starter · #12 ·
The GMC dealership called today and the Acadia will be back in the shop tomarrow. I was advised that the engineers tested the wiring and found the same problem, they told the dealership that they found a fix which involves running a by-pass wire. I not sure what that mean, but I will be happy once its work correctly. I'll post an update tomarrow.
 

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Discussion Starter · #13 ·
Its not a trailer problem as confirmed with the GMC engineers. My surge brakes have an electrical. When the vehicle is placed in reverse it should activate the cylinder which allows the trailer to back up and apply the brakes. My wiring from the trailer has a 5 flat connector whith a round adapter. The extra wiring provided in the Acadia is for electric trailer brakes only, dosn't apply to this problem.
 

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Please let me know what they come up with for you. I am asking people in our quality department if they are aware of this issue.

Thanks
 

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Hi, Crash 286
I have a electronic background and have also installed trailer wiring from scratch in several vehicles.
The factory installed trailer wiring harness was never intended for deactivating trailer brakes. The only function of the brake wire in the harness is to activate electric brakes on trailers if the brake wire in your harness is connected to a brake controller in your vehicle. The electric deactivated surge brakes is a newer technology and the vehicle manufacturer has not incorporated this in the factory installed wiring harness. There is a way to do this however, a separate wire has to be spliced to your vehicle backup light circuit and attached to your surge brake deactivating solenoid. As you put the vehicle in reverse, the solenoid on your surge brakes is energized when the backup lights are energized. Hope this helps.
 

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I did a little research last night. Not sure if I have this problem but I will check later today with a voltmeter. I have used the lights on my trailer with a 4 pin adapter and had no problem, so the issue appears to be with the other 3 lugs.

According to the owner's manual, the lt green wire is supposed to be a backup wire. It is wired to the central lug and it appears it is supposed to be used for exactly what he wants- deactivating a surge brake provided with an electrical solenoid. The industry standard just calls the center post on the 7 lug RV connector "auxiliary"- it can be used for anything you want with no particular standard. The book also talks about the other 12V and brake lugs-"The fuses for these two circuits are installed in the underhood electrical center, but the wires are not connected. They should be connected by your dealer/retailer or a qualified service center." Since these two are not connected at the factory maybe the backup circuit is also not connected. Should be an easy fix though.
 

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crash2864 said:
My wiring from the trailer has a 5 flat connector whith a round adapter.
Did you check the voltage at the 7 lug on the car or on your flat 5 pin connector?

Here is a description of a 7 lug to 5 pin converter... "7-WAY TO 5 WAY CONNECTOR ADAPTER Converts 7-way Blade Connector Socket to a 5- way Molded Connector. Allows one vehicle to tow campers or boat trailers with electric brakes."

Based on this description, the 5th pin is connected to the brake line (which we know is not connected) and not the center "backup" lug.

Just a thought. Hope they figure it out.
 

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Hopefully, your dealer got it figured out today.

I checked my center post and found it is also not energized with the car in reverse. I did find that the 12 volt terminal was live, which according to the book, is not supposed to be hooked up. Maybe it's just a typo in the manual and the backup and brake lines need to be connected at the fuse box and not the brake and 12V lines.

I still would be very careful that the 7 way to 5 way connector you have is correct. You may solve the vehicle problem and still not get the brake solenoid working because it's powered off the wrong pin.
 

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Discussion Starter · #19 ·
Took the Acadia to the dealership today..They did some sort of wire by-pass, as recommended by the GM engineers. Took it home and every thing worked great!! Thank god....The dealership advised me that the engineers were waiting to hear back from them to to confirm the problem in the wiring harness is fixed.. they will sending out a memo to the dealerships on the fix. They said that this was the first they had seen, and after it was brought to their attention and after testing other Acadias it was an oversight in the trailer wiring.

All lights and signal worked, and when I put it in reverse the trailer brakes were de-activated and I was able to back the trailer up..So I would strongly advise checking your wiring prior to hooking up a trailer..I'm still every impressed with the Acadia..and glad I traded my Denali for it..Its a great vehicle!!
 

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Would this new TSB help you?

Subject: Supplemental Information on Recreational Vehicle and Trailer Towing and Trailer Wiring Accommodation for Non-V92 Equipped Vehicles #07-00-89-021A - (06/27/2007)

Models: 2008 Buick Enclave

2007 GMC Acadia

2007 Saturn OUTLOOK

This bulletin is being revised to add models and revise dinghy towing procedures. Please discard Corporate Bulletin Number 07-00-89-021 (Section 00 - General Information).

The purpose of this bulletin is to inform dealers of special procedures necessary when towing a trailer or when towing the vehicle behind a recreational vehicle.
Towing a Trailer

Trailer Weight Information
The following chart shows how much the trailer can weigh, based on the vehicle powertrain combination. Retailers should refer customers to the appropriate Owner Manual for important trailering tips, vehicle maintenance, and safety rules before towing a trailer.
Vehicle Maximum Trailer Weight
3.6L V6 (LY7) Engine with Front-Wheel Drive and 6-Speed Automatic Transaxle (MY9) with Trailer Provisions (V92) 4,500 lb. (2,041 kg)
3.6L V6 (LY7) Engine with Front-Wheel Drive and 6-Speed Automatic Transaxle (MY9), NO Trailer Provisions 2,000 lb. (907 kg)
3.6L V6 (LY7) Engine with All-Wheel Drive and 6-Speed Automatic Transaxle (MH6) with Trailer Provisions (V92) 4,500 lbs. (2,041 kg)
3.6L V6 (LY7) Engine with All-Wheel Drive and 6-Speed Automatic Transaxle (MH6), NO Trailer Provisions 2,000 lb. (907 kg)
Towing a Trailer with a Vehicle NOT Equipped with Trailer Provisions
2008 Buick Enclave, 2007 GMC Acadia and 2007 Saturn OUTLOOK vehicles that are not equipped with trailer provisions (RPO V92) must be modified with a new underhood bussed electrical center (UBEC) to provide full functionality for 4 circuits: ground, tail lamps, RH and LH stop/turn lamps. Refer to the Parts Information section in this bulletin for the correct part numbers. To find the original part number, remove the UBEC and look at the side of the UBEC.
This UBEC replacement should only be performed for customers who perform trailer towing. UBEC replacement for trailer towing is only covered under warranty for 2007 model year GMC Acadia and Saturn OUTLOOK vehicles, and 2008 Buick Enclave vehicles.
Towing a Trailer with a Vehicle with Trailer Provisions (RPO V92)
The following procedure may need to be performed to the backup lamp circuit. Perform this procedure only if the customer will be using the vehicle to tow.
1. Disconnect the X7 connector from the Body Control Module (BCM).
2. Remove the terminal for pin 3 from the BCM X7 connector. The wire to this terminal is dark blue and is the 38 circuit.
3. Re-connect the X7 connector to the BCM.
4. Cut the terminal off the end of this wire and strip the end of the wire.
5. Splice this wire into the 24 circuit wire that goes into BCM connector X6, pin 2. The 24 circuit is light green.
Recreational Vehicle Towing (Dinghy Towing)

Important: To avoid battery rundown while towing, remove the 50 amp BATT1 fuse in the UBEC. Refer to the dinghy towing procedure in this bulletin.
Recreational Vehicle Towing Information
Important: Vehicles with a 6-speed automatic transmission that are "dinghy towed" must be started at the beginning of each day and at each fuel stop for a minimum of five minutes.
Recreational vehicle towing means towing the vehicle behind another vehicle -- such as behind a motorhome. The two most common types of recreational vehicle towing are known as "dinghy towing" (towing the vehicle with all four wheels on the ground) and "dolly towing" (towing the vehicle with two wheels on the ground and two wheels up on a device known as a "dolly"). With the proper preparation and equipment, many vehicles can be towed in these ways. Refer to the appropriate model/model year Owner Manual for towing preparation guidelines and dolly and dinghy towing procedures. The Towing Chart below summarizes powertrain combination compatibility with dolly and dinghy towing methods.
2008 Buick Enclave, 2007 GMC Acadia, 2007 Saturn OUTLOOK Recreational Vehicle Towing Chart

Powertrain Combination and Towing Method Rear Wheels on a Tow Dolly Front Wheels on a Tow Dolly All Four Wheels on the Ground (Dinghy)
3.6L V6 (LY7) Engine with Front-Wheel Drive and 6T75 Six-Speed Automatic Transaxle (MY9) No Yes Yes*
3.6L V6 (LY7) Engine with All-Wheel Drive and 6T75 Six-Speed Automatic Transaxle (MH6) No No Yes*
*Notice: If the vehicle is equipped with a 6T75 six-speed automatic transmission, it can be dinghy towed from the front for unlimited miles at 65 mph (105 km/h). To avoid vehicle damage, never exceed 65 mph (105 km/h) while towing Buick Enclave, GMC Acadia and Saturn OUTLOOK vehicles. The repairs would not be covered by the warranty.
Dinghy Towing Procedure
Notice: If you tow your vehicle without performing each of the steps listed under "Dinghy Towing," you could damage the automatic transmission. Be sure to follow all steps of the dinghy towing procedure prior to and after towing your vehicle.
Notice: Don't tow a vehicle with the front drive wheels on the ground if one of the front tires is a compact spare tire. Towing with two different tire sizes on the front of the vehicle can cause severe damage to the transmission.
Important: Buick Enclave, GMC Acadia and Saturn OUTLOOK vehicles may only be dinghy towed from the front, with all four wheels on the ground.
1. Position the vehicle to tow and then secure it.
2. Shift transmission to PARK (P) and turn the ignition to OFF.
3. Set the parking brake.
4. Turn the ignition to ACCESSORY.
5. Shift your transmission to NEUTRAL (N).
6. To prevent your battery from draining while the vehicle is being towed, remove the 50 amp BATT1 fuse in the UBEC, and store in a safe location.
7. Release the parking brake.
Once you have reached your destination, do the following steps:
1. Set the parking brake.
2. Reinstall the BATT1 fuse.
3. Shift the transmission to PARK (P), turn the ignition key to OFF and remove the key from the ignition.
4. Release the parking brake.
Parts Information

Part Number Description
25784721 Underhood Bussed Electrical Center
(replaces 25784722)
25784723 Underhood Bussed Electrical Center
(replaces 25784726)
25784725 Underhood Bussed Electrical Center (replaces 25784724)
Warranty Information

For vehicles repaired under warranty, use:
Labor Operation Description Labor Time
N1730 Block Assembly, Wiring Harness Junction - Engine - Replace 0.3 hr

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

© Copyright General Motors Corporation. All Rights Reserved.

" name=forward Document ID# 1993341
 
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