When I recently decided to purchase a semi-lightweight travel trailer, I assumed it would be an easy thing to add a hitch with full trailer electrical and brake functions to my 2015 X5 35d. Little did I know I was wading into one of the more controversial and complex aspects of owning an X5...
Is it an abomination to have a visible hitch on a BMW? Should you tow with an X5 in the first place? If you get past these issues, then you're dealing with what hitch is best? OEM? Invisihitch? Something else? And then if the hitch decision wasn't painful enough, you need to figure out what wiring harness is the right choice? OEM? Aftermarket? Active? Passive?
There are nearly as many opinions about what is best as there are options. In one sense, that means there are a lot of good options and what is "right" may come down to exactly what the needs are. For me, my needs drove the decision and I'm very pleased with the end results.
My needs/wants:
After weighing several wiring harness options, I decided to go with the full OEM setup. This meant the OEM harness, the OEM hitch control unit, and the OEM brake controller (Tekonsha head with the proprietary BMW cable).
After calling a local hitch installer and getting quoted over $1700 and 5 weeks for the parts, install and coding, I hung up and decided to do the job myself. Here are the parts used and where they were purchase from:
When the 47 lb package from Curt arrived, I wasn't disappointed. The quality of design, welds and finish on the Curt hitch were all outstanding. I was even more impressed when I realized they had included replacement plastic fasteners for the wheelwell trim - unexpected and truly a great addition to their hitch package. The other items all looked in great shape as well, but I will say the hitch harness raised my eyebrows as I realized I would have to add some pins to some existing vehicle plugs to complete the wiring. I was hoping for a plug-n-play install, but it is slightly more involved than that.
Removing the rear bumper fascia without damaging anything is a PITA, but doable in an hour or so being very careful.
I followed the excellent instructions from invisihitch for most of the job. They truly do a fantastic job walking through every step. I also used the BMW instructions for retrofit of the OEM removable trailer tow hitch. Although these instructions are not for the exact hitch and harness I installed, the harness is substantially similar and these instructions showed how to complete each of the pins into the back of the fuse panel, which is a bit different than for the Invisihitch harness.
The Curt hitch installs onto the factory studs for the rear bumper crash bar (it replaces the bar) and was a perfect fit - slid right on. After torquing the 8 nuts supplied with the hitch, I began the wiring installation. The wiring in the luggage compartment all went without a hitch (no pun intended).
I did have some difficulty finding the vehicle connector for the Body Domain Controller, as it was hidden inside the chassis harness and wrapped in tape. You can see it in the lower right of the image above, after being exposed.
Here is a closer view of the Body Domain Controller connection.
I also had some difficulty reading the pin numbers on the CANBUS terminal plug behind the fuse box. Two of the OEM towing harness wires must be pinned into this connector and figuring out how the connector was numbered required a magnifying glass. Below is a cheat sheet on how the pins are sequenced for anyone trying to do this task (these pinouts are required for almost all active harness designs, not just the OEM harness).
After this, completing the wiring inside the vehicle was mostly straightforward. The finished install is very clean, with the brake control plug easily accessible for whenever I am towing.
The external wiring was a different matter. The Curt hitch tucks in so tightly under the bumper fascia that there is no place to mount a hitch plug bracket on the hitch itself. Hanging the plug on a bracket below the bumper is ugly (my opinion) and also there is the problem of there being no substantial structure in the bottom of the bumper fascia to attach a plug bracket into. For this reason, I designed a bracket which adds some structure to the bottom of the bumper and holds the plug receptacle in a way that is hidden when it is not being used.
This required a curved sheet metal bracket with some welded stiffeners on it to keep lower fascia from flexing when inserting the plug and when carrying the weight of the heavy trailer wiring over rough roads.
This curved sheet bracket was epoxied to the inside of the bumper fascia and was extended far enough outboard to catch the first support screw between the fascia and the chassis insulating panel. It is not pretty when viewed from inside the bumper, but I wanted to corrosion-proof the steel bracket as well as I could, given its location.
The final install looks about as good as I could have hoped, given the fact I now have a permanently visible 2" receiver under my bumper. The Curt design tucks the receiver up exactly to the point where it is nearly touching the bumper and also holds it back under the car about as far as is practical. The Curt hitch does all it can to hide the receiver, short of going to the hidden hitch design.
Finally, even without encoding the control unit to the vehicle or doing any coding, most of the tow functions came alive after install. All trailer lights work and the X5 recognizes when a trailer is attached and disables rear PDC, replacing the radar PDC graphic and alerts with a tow symbol. The camera zoom feature did not activate and I suspect the active suspension features have not activated either. I am getting a "Hitch Wiring Failure" amber warning on the dash which made my heart sink a bit, but when I check the codes the only fault present is that the control unit is not encoded to the vehicle. I will get the box encoded and any needed features activated in the coming week or so and hopefully that will finish the job.
Total cost: $789 + another $100 or so for coding.
Total time: About 7 hours and 2 of those were spent fabricating the hitch plug bracket.
Next report, I will let you know how the 35d pulls the trailer when fully loaded - I expect this will be around 5,000 lbs. I have high expectations from this little diesel, I know. If it feels a bit anemic, I will be working on the ECU next!
Hopefully someone will find this useful and don't hesitate to hit me up with questions.
-PNWX5
Is it an abomination to have a visible hitch on a BMW? Should you tow with an X5 in the first place? If you get past these issues, then you're dealing with what hitch is best? OEM? Invisihitch? Something else? And then if the hitch decision wasn't painful enough, you need to figure out what wiring harness is the right choice? OEM? Aftermarket? Active? Passive?
There are nearly as many opinions about what is best as there are options. In one sense, that means there are a lot of good options and what is "right" may come down to exactly what the needs are. For me, my needs drove the decision and I'm very pleased with the end results.
My needs/wants:
- Trailer dry weight - 4,000 lbs
- Tongue weight - 500 lbs
- Trailer braking - Yes
- Preferred brake controller - Active hardwired (not an inertial bluetooth unit)
- Chassis or bumper modifications - No
- Preferred hitch ball - 2-5/16 inch
- Preferred hitch features - Load-leveling and anti-sway
- Car integration - to the greatest degree possible, but willing to compromise
After weighing several wiring harness options, I decided to go with the full OEM setup. This meant the OEM harness, the OEM hitch control unit, and the OEM brake controller (Tekonsha head with the proprietary BMW cable).
After calling a local hitch installer and getting quoted over $1700 and 5 weeks for the parts, install and coding, I hung up and decided to do the job myself. Here are the parts used and where they were purchase from:
- Curt hitch - Part# 13077 - $193 through Amazon
- OEM tow hitch wiring harness - Part# 82-71-2-349-500 - $216 through Irvine BMW
- OEM trailer hitch control unit - Part# 71-60-6-884-357 - $85 from a wrecking yard
- OEM brake controller and cable - Part# 82-11-0-420-082 - $210 through Suburban Auto Parts
When the 47 lb package from Curt arrived, I wasn't disappointed. The quality of design, welds and finish on the Curt hitch were all outstanding. I was even more impressed when I realized they had included replacement plastic fasteners for the wheelwell trim - unexpected and truly a great addition to their hitch package. The other items all looked in great shape as well, but I will say the hitch harness raised my eyebrows as I realized I would have to add some pins to some existing vehicle plugs to complete the wiring. I was hoping for a plug-n-play install, but it is slightly more involved than that.
Removing the rear bumper fascia without damaging anything is a PITA, but doable in an hour or so being very careful.
I followed the excellent instructions from invisihitch for most of the job. They truly do a fantastic job walking through every step. I also used the BMW instructions for retrofit of the OEM removable trailer tow hitch. Although these instructions are not for the exact hitch and harness I installed, the harness is substantially similar and these instructions showed how to complete each of the pins into the back of the fuse panel, which is a bit different than for the Invisihitch harness.
The Curt hitch installs onto the factory studs for the rear bumper crash bar (it replaces the bar) and was a perfect fit - slid right on. After torquing the 8 nuts supplied with the hitch, I began the wiring installation. The wiring in the luggage compartment all went without a hitch (no pun intended).
I did have some difficulty finding the vehicle connector for the Body Domain Controller, as it was hidden inside the chassis harness and wrapped in tape. You can see it in the lower right of the image above, after being exposed.
Here is a closer view of the Body Domain Controller connection.
I also had some difficulty reading the pin numbers on the CANBUS terminal plug behind the fuse box. Two of the OEM towing harness wires must be pinned into this connector and figuring out how the connector was numbered required a magnifying glass. Below is a cheat sheet on how the pins are sequenced for anyone trying to do this task (these pinouts are required for almost all active harness designs, not just the OEM harness).
After this, completing the wiring inside the vehicle was mostly straightforward. The finished install is very clean, with the brake control plug easily accessible for whenever I am towing.
The external wiring was a different matter. The Curt hitch tucks in so tightly under the bumper fascia that there is no place to mount a hitch plug bracket on the hitch itself. Hanging the plug on a bracket below the bumper is ugly (my opinion) and also there is the problem of there being no substantial structure in the bottom of the bumper fascia to attach a plug bracket into. For this reason, I designed a bracket which adds some structure to the bottom of the bumper and holds the plug receptacle in a way that is hidden when it is not being used.
This required a curved sheet metal bracket with some welded stiffeners on it to keep lower fascia from flexing when inserting the plug and when carrying the weight of the heavy trailer wiring over rough roads.
This curved sheet bracket was epoxied to the inside of the bumper fascia and was extended far enough outboard to catch the first support screw between the fascia and the chassis insulating panel. It is not pretty when viewed from inside the bumper, but I wanted to corrosion-proof the steel bracket as well as I could, given its location.
The final install looks about as good as I could have hoped, given the fact I now have a permanently visible 2" receiver under my bumper. The Curt design tucks the receiver up exactly to the point where it is nearly touching the bumper and also holds it back under the car about as far as is practical. The Curt hitch does all it can to hide the receiver, short of going to the hidden hitch design.
Finally, even without encoding the control unit to the vehicle or doing any coding, most of the tow functions came alive after install. All trailer lights work and the X5 recognizes when a trailer is attached and disables rear PDC, replacing the radar PDC graphic and alerts with a tow symbol. The camera zoom feature did not activate and I suspect the active suspension features have not activated either. I am getting a "Hitch Wiring Failure" amber warning on the dash which made my heart sink a bit, but when I check the codes the only fault present is that the control unit is not encoded to the vehicle. I will get the box encoded and any needed features activated in the coming week or so and hopefully that will finish the job.
Total cost: $789 + another $100 or so for coding.
Total time: About 7 hours and 2 of those were spent fabricating the hitch plug bracket.
Next report, I will let you know how the 35d pulls the trailer when fully loaded - I expect this will be around 5,000 lbs. I have high expectations from this little diesel, I know. If it feels a bit anemic, I will be working on the ECU next!
Hopefully someone will find this useful and don't hesitate to hit me up with questions.
-PNWX5