2018 CX-9 Power Liftgate won't respond

[Rich G]

Power liftgate won't respond to dash, gate or key fob buttons. The fuse in driver-side foot bay fuse box is fine and I tried the reset button on lift gate that beeps, but none of that fixed the problem. The only thing that I did differently was had U-haul install a trailer hitch with wiring to the vehicle about a week before so that I could tow one of their trailers over 2 days. The tailgate worked while loading the CX9, but didn't work when I got to destination ~ 1,400 miles down Rt 95 from PA to FL. One other thing, when I had the trailer hooked up to the wire harness overnight before trip, the battery drained and I had to jump start the CX9 so for caution, I disconnected the wire harness from the trailer when we stopped for an overnight. The next morning, the CX9 started right up and I reconnected the wire harness to the trailer.

Any ideas to test motor(s)/electric? I am not a mechanic, but am not afraid to get grease on my hands....

Thanks

 

[sm1ke]

What happens when you use any of the buttons to open the liftgate? Does it just beep 3 times? Have you tried to open it manually from the inside of the car?

Have you tried disconnecting the negative terminal on the battery, then pressing and holding the brake pedal down to drain electricity from the system, and then reconnecting the negative terminal and starting the car?

 

[youri]

What type of trailer connector did you get installed? (4 pins, 7 pins ? ). I am wondering if they messed up your wiring when they did the installation. Do you have a list of parts they used that shows the part number of the wiring harness? Normally a four pin harness to the cx-9 does not require any splicing and is just a quick connect in an empty connector, but they could have “hand made” it and spliced into the tailgate wiring.

If you battery drains when the trailer is plugged in with a four pin flat connector and your car lights turned off then i would think that something is up with the wiring. This may or may not be related with the tailgate, but it is possible.

 

[200955]

You'll have to open the gate from the inside and lift the panel fully slowly - it will need to be supported as I doubt it will stay up on it's own. Running along the outside of the gate are two pinch prevention strips that stop the gate immediately if something gets between the gate and the body. Bet you didn't know these existed. Examine both closely for damage - deformed or collapsed or possibly ripped. They are towards the top and often mistaken for weather strip. If they look OK the next step will be to determine if power is actually reaching the motors. The top panel of the gate can easily be removed by removing the push pins and just pulling it off. Connectors for both are in plain sight. Unplug them and using a VOM meter check the supply side of the connector for voltage while someone else activates the switch. Both connectors have to be DISCONNECTED so both motors are disabled. If no power is found at these connectors best you reassemble everything and head back to U-Haul as it is probably something they did. If they used a welder to install the hitch that's not good.
Let them figure it out. Once reassembled, lift the hatch as high as it will go then lower it to latch and then try activation button.

 

[Rich G]

Thank you for the feedback, I do suspect that the installer of the 4 Pin wire harness didn't do it properly. I'll start there and then proceed to the negative battery disconnect and other suggestions if needed.
In the meantime, I've been crawling into the back to manually open the lift gate by pressing the emergency release lever. Makes me wonder why Mazda doesn't provide an external access like they do to open the doors with a Key in the key fob.