Help me fix my boot sensor-(multimeter and resistor experts)

[1083 Feedbacks]

Wonder if any wise man (or woman) could shed any light on my boot issue.

I have a boot (surprise surprise) that is showing as OPEN on my dash, even when its closed. Checked everything to make sure no water damage, which it isn't.

I noticed under the bottom sill where the boot latch goes into, theres 2 small micro switches.

I have removed this part and have been testing it on a multimeter. So at the moment, with the boot OPEN the micro switch buttons are pressed in.

LEFT/RED MICROSWITCH is showing 000.1ohm (it beeps to indicate a circuit) and if i open the switch (so the button isn't pressed in) it shows 469.4ohm (it doesn't beep to indicate a circuit)

RIGHT/BLUE MICROSWITCH is showing 468.6ohm (it doesn't beep to indicate a circuit) and if i open the switch (so the button isn't pressed in) it shows 000.1ohm (it beeps to indicate a circuit)

So it looks like the readings are opposite each other. I am thinking the right/blue one is faulty? if so... Perhaps I could use a resistor to fool the system? or tape in the button so it always shows a closed connection?

I cannot work out which microswitch is faulty. And Im not sure what I could do to repair this? would a resistor work? if so what spec resistor? I just want the image on my dash to go away and show the boot as closed. I don't care what it shows when its actually open.

Edited by 1083 Feedbacks on Thursday 24th May 18:40

[Elliot2000]

I reckon they are doin what they are supposed to be doing and u may have an issue in the wiring. How many wires are go to the connector? What car is it?

You probably have one redundant microswitch, and one that is supposed to be used. One that is normally open and one normally closed. If u only have two wires goin to the connector - with it disconnected I assume u still have the light on, you can thebnbridge across the two wires - if your light is still on then the problem is definitely either to do with the wiring or the ecu

Edited by Elliot2000 on Thursday 24th May 19:17

[E-bmw]

The easy way to tell if one is incorrect is to operate each in turn & see if the boot open light goes out with one combination or other, if it doesn't then that isn't your problem.

[Penelope Stopit]

Visit here, read all the page and then do a test the same as mentioned in the 05-16-2016, 06:18 PM Post by username - trackfactory

https://www.audiworld.com/forums/q7-discussion-112...

The above user measured the voltages with the micro-switches connected up

Good luck, post back if you're stuck

[GreenV8S]

E-bmw said:

The easy way to tell if one is incorrect is to operate each in turn & see if the boot open light goes out with one combination or other, if it doesn't then that isn't your problem.

I agree. Depending how the switches are mounted, it may be necessary to unmount them (leaving them connected electrically) to test them.

[1083 Feedbacks]

Ah you legends, good advice!.

@ penelope - thats the exact switches I have on my Q7 from that forum link.

[Penelope Stopit]

No problem, glad to be of help
With those switches being on the CAN BUS there is a very good chance that they have built in resistors, and it makes sense that they are using 2 switches of opposite operation 1 x normally open and 1 x normally closed so as to be able to use one switch as a reference against the other and vice versa.......If one switch is showing on the CAN as closed the other should be showing as open......they should always be opposites to one another hence the on CAN control unit will recognise/see a faulty switch if it gets 2 open signals or 2 closed signals at the same time rather than opposites

The problems arise when both switches have failed

[1083 Feedbacks]

Penelope Stopit said:

No problem, glad to be of help
With those switches being on the CAN BUS there is a very good chance that they have built in resistors, and it makes sense that they are using 2 switches of opposite operation 1 x normally open and 1 x normally closed so as to be able to use one switch as a reference against the other and vice versa.......If one switch is showing on the CAN as closed the other should be showing as open......they should always be opposites to one another hence the on CAN control unit will recognise/see a faulty switch if it gets 2 open signals or 2 closed signals at the same time rather than opposites

The problems arise when both switches have failed

I see, so as mine is showing one open and one closed in the same positions, are you saying that is correct?

If so, Its back to the drawing board for me as to why my boot is saying its open still when its not.

[GreenV8S]

If you confirm that the boot warning goes away when you operate both switches, the next step would be to connect a meter up and see whether the switches are actually switching when you close the boot. Typically in my experience these switches are positioned so that the boot has to be fully closed to operate them, and perhaps the boot latch position and/or switch positions need adjusting so that the boot operates the switches properly.

[1083 Feedbacks]

GreenV8S said:

If you confirm that the boot warning goes away when you operate both switches, the next step would be to connect a meter up and see whether the switches are actually switching when you close the boot. Typically in my experience these switches are positioned so that the boot has to be fully closed to operate them, and perhaps the boot latch position and/or switch positions need adjusting so that the boot operates the switches properly.

Just checked, Makes no difference.

The lock latch motor makes a lot of noise though. More than it used to.

[1083 Feedbacks]

Just to add to all this. The tail lights randomly stop working too!. At the moment, they're working though.

[GreenV8S]

1083 Feedbacks said:

Just checked, Makes no difference.

Checked what?

[Penelope Stopit]

1083 Feedbacks said:

Just to add to all this. The tail lights randomly stop working too!. At the moment, they're working though.

Have you downloaded and read these PDF files from the website I linked you to?

https://www.audiworld.com/forums/attachment.php?at...

https://www.audiworld.com/forums/attachment.php?at...

There seems to be a 4 year or 50,000 miles warranty on some of this work

[1083 Feedbacks]

GreenV8S said:

Checked what?

The microswitches one by one to see if the boot open warning light goes away.

Makes no difference.

[1083 Feedbacks]

Penelope Stopit said:

Have you downloaded and read these PDF files from the website I linked you to?

https://www.audiworld.com/forums/attachment.php?at...

https://www.audiworld.com/forums/attachment.php?at...

There seems to be a 4 year or 50,000 miles warranty on some of this work

I read those, but I don't get any error on the dash about the lights being malfunctioned.

The specific error code also isn't present in the mentioned modules.

I have VCDS and have various scans of the car today.

[GreenV8S]

1083 Feedbacks said:

The microswitches one by one to see if the boot open warning light goes away.

Makes no difference.

The behaviour of the switches seems reasonable. The car doesn't seem to be recognising the switch positions correctly.

If that was me, my next step would be to investigate how they're connected. I suspect normal operation would be for each switch to have some voltage across it in the high resistance position and for that to drop to roughly zero when the switch is in the low resistance position. The voltages in the high resistance position ought to be similar for both switches.

[Penelope Stopit]

Ok, Do you get the same voltage readings as in the test over at that website, the readings of 6.4 something and 6.5 something volts ( I can't remember the exact voltages)
I reckon that if those or close to those voltages are found it proves the wiring to the control unit is good
I appreciate you measured resistances earlier but what about voltages with the switches in the circuit and tested as over at that website

[1083 Feedbacks]

I managed to fix it.

It was the motor that draws the boot into its locked position that was the problem.

£49 for the part and 10 minute job to replace it.