RRS - Upper Tailgate Unlocking on Start

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Originally Posted by garrycol

the pulse to run the motor is coming from somewhere but not sure if this is a result of the relevant computer not getting getting correct signal back or is just a stray pulse being generated by the system

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The power to the motor is switched using a FET within the BCU. It uses a very simple electrical setup so something is telling the BCU to open the glass (most likely the switch wire) - it wont be a stray pulse.

In pulling the rear door trim off, I noted that unlike just about all other panels on these cars you just do not pull it off - some manipulation is required - I just pulled it off so bits of broken plastic went flying everywhere :(.

I did find a sub woofer in the back door - I have the mid range radio and I did not think it had a sub woofer which I thought was only in the top range radio. If I do have a sub woofer, do I have a amp to drive it or is it just driven by the radio.

Garry

Garry you're keen at this time of night!

I have no idea about your speakers but vibration from the engine starting and idling could be causing the switch wire with worn-through insulation to momentarily touch the bodywork, perhaps at the spots where the wiring exits the door frame or enters the body. Even just manipulating the rubber shroud might cause it to continually operate the motor or fix it for the moment.

Thanks Graeme - while I do not think that is the issue I will check it out. Interestingly when the doors are locked I do not have the issue. I will also take the unlock function out of the main key fob as I assume it changes the programming in the relevant section of the computer - again I don't think it will fix anything but is worth a try.

No fault codes are now showing up.

If the issue is still there next week I will do just what the dealer will do and start replacing parts.:(

Thanks to everyone for your input - looks like no one has had this locally and the one in the UK was fixed by replacing the latch switch which I don't believe is my issue.

Thanks

Garry

If there is an intermitant short in the wiring between the switch and the bcu then connecting a voltmeter across the switch terminals with the engine idling should show the voltage (either 5V or 12V) momentarily dropping to zero.

Thanks Graeme - I will put the multimeter on it tomorrow and see what it does.

Oh - the fault code is back. B1C42 - Tailgate Release Switch 2 - Signal Failure - Signal Stays Low.

Does anyone have detailed information on this.

cheers

GARRY

Signal staying low is indicating a connection to ground somewhere, as though someone is holding the switch for an excessive time. The signal is "high" when at its 5V or 12V (whichever is used) then pulled low to earth by operating the switch.

Well I will be ..........

After a week with this problem I went out to the car to do the checks suggested by Graeme and to trace some cables to see if there was anywhere where they may have been chaffed and creating shorts.

I started the car and there was no unlocking of the rear tailgate - I switched off and restarted 10 times and no issue - so I went for a drive and no opening of the rear tailgate :confused:.

I am not going to put the trim back just yet but it would seem that after a week the problem has just gone away.

I am beginning to think that these cars have a mind all of their own:(.

Edit - could this issue be caused by low voltage in the battery?? The only reason I raise this is that the radio did show low power a couple of times, the cables to the switches etc in the tailgate are very small and and at the far end of the car and the fault codes did show voltage low. The radio is no longer showing low power so the battery must be back up.

Garry

Garry,
I do not think that low battery will have an effect on the tail gate opening. It needs to be switched. Otherwise there would be tail gates opening everywhere in winter!

Just by removing the trim may have relieved the pressure on a wire shorting to earth.

Check all the wires in the tailgate, it is time consuming but worth it.
Also check & see the wiring in the roof at the rear, there are a bunch of multiplugs just above the roof lining & one could be under pressure.

Cheers & Good luck.

Sent from my iPad using Forum Runner

I agree symptoms do seem the be related to something shorting or leaking voltage somewhere.

I am now thinking water in the system somewhere. When the problem started it had been raining for a few days and the car had been parked outside, now that the weather has stopped raining and the humidity low the issue has gone leading me to think that some crucial spot got a little damp. The switch was damp but with it disconnected the problem still continued.

Power for the system comes from the Central Junction Box and may be the culprit if it can be exposed to moisture. So where is this CJB so I check it for corrosion/moisture.

Thanks

Garry