Technical Boot/trunk latch doesn't works at all!

[anyzunstudios]

Hi, after a year with my lovely GP, I have decided to fix boot/trunk because it does not turns trunk light on when it is open. After reserching on Internet, I have found that when my trunk is open, car Displays at dashboard that trunk is open too, but mine does not do anything. I thought that this car doesn't have that message (and that sounds to me really weird because this car is f*cking always with messages like license plate lights Canbus error because and they are LED with Canbus error removal!) So I think that latch is f...ed. I test it with a multimeter, pin 1 gives always 12v, pin 2 (I think is broken) it gives 0.01v when you press button to open trunk, 3 is negative 12v, and 4 is open trunk latch signal (12v to open).
Trunk open and close, but no light (this really bothers me at night), no messages at Display (sometimes I drive with trunk open because latch doesn't close properly or I don't close at all trunk, and It is a problem if trunk opens).

Any help or idea? Some People say that changing latch doesn't fix the poblem, It might be wire stuff. What do you recomend to me? Can I test manually if problem is latch or wires faking latch sensor? If I can, how can I?

Thanks in advance!

 

[portland_bill]

As far as I understand it, there is a switch in the latch that tells the computer when the trunk is open. As this is just a signal, it may be anything up to 12v, so your 0.01v may be correct. What you need to determine is whether this goes from zero to a voltage when the latch is opened.

With the trunk open, close the latch, as if the trunk is closed. A screwdriver blade or similar will do this. Then attach your meter to the signal connection, and 'open' the latch. See if the voltage changes. If it does not change, the switch on the latch is not working. A dose of contact cleaner may fix it. If it does change, we'd need to know the voltage, and of course, what it is expected to be. Lots of CanBus signals are very low voltages, so the 0.01v may be correct. Putting a higher voltage down that wire to the computer may be a good test, but don't know what a higher voltage might do.

Next need to check whether the voltage is getting through the wires to the computer. Where the wiring passes from door to body is a weak point for cable failure. Find the end inside the car and see if the signal voltage gets through.

 

[aurick86]

Use a power limiting resistor in series with the 12v on the latch put that through the wire with 0.01v, if you get a boot open message then you know the latch has a broken switch... you might be able to fix it by taking it apart. if not just replace it.

The power limiting resistor should prevent anything geting fried if there shouldn't be voltage there.
As to the exact resistor .. not sure maybe 1k ohm 0.5w

 

[DGPunto]

First thing I would do is have a look at the wiring between the body and the hatch. There's a little concertina'd rubber tube at the top right between the two. Usually brake lights and the washer suffer from wires breaking in there.

 

[anyzunstudios]

As far as I understand it, there is a switch in the latch that tells the computer when the trunk is open. As this is just a signal, it may be anything up to 12v, so your 0.01v may be correct. What you need to determine is whether this goes from zero to a voltage when the latch is opened.

With the trunk open, close the latch, as if the trunk is closed. A screwdriver blade or similar will do this. Then attach your meter to the signal connection, and 'open' the latch. See if the voltage changes. If it does not change, the switch on the latch is not working. A dose of contact cleaner may fix it. If it does change, we'd need to know the voltage, and of course, what it is expected to be. Lots of CanBus signals are very low voltages, so the 0.01v may be correct. Putting a higher voltage down that wire to the computer may be a good test, but don't know what a higher voltage might do.

Next need to check whether the voltage is getting through the wires to the computer. Where the wiring passes from door to body is a weak point for cable failure. Find the end inside the car and see if the signal voltage gets through.

I have tested it and It does It, It changes from 0v to 0.01v when trunk opens, but it takes about a second to change to 0v. I don't know if It is due to voltage drop-down when turn signals, instrument cluster, ECU computer, and latch turns at same time, or it might be a result of the crappy materials quality of my cheap chinese multimeter,and sometimes gets wrong values [emoji28]

 

[portland_bill]

This is the text in eLearn (Factory workshop manual) for the Panda.

Functional description
The front courtesy light G010 is supplied by the body computer node M001 (pin 10 connector F). The internal switch A can be turned to three positions:

position 0: the switching on or off of the front courtesy light is managed by the body computer node;
position 1: the front courtesy light is always off;
position 2: the front courtesy light is always on.
The body computer node switches the front courtesy light on automatically in relation to the door signals coming from the door locks N050, N051, N055 and N056 in the following conditions:

if the negative signal (with reference to earth C020 connector B) indicating the left front door opening is received at pin 23 connector H;
if the negative signal (with reference to earth C020 connector B) indicating the right front door opening is received at pin 21 connector H;
if the negative signal (with reference to earth C030) indicating the left rear door opening is received at pin 15 connector G;
if the negative signal (with reference to earth C020 connector A) indicating the right rear door opening is received at pin 4 connector G;
if the negative signal (with reference to earth C020 connector B) indicating the unlocking of the doors (central unlocking) is received at pin 13 connector H;
if the negative signal (with reference to earth C030) indicating the operation of the inertia switch I050 is received at pin 14 connector G.
The connection between the body computer node and the front locks N050 and N051 passes through the door couplings D030 connector A and D031 connector A. Both are housed, in the passenger compartment area, in the lower part of the left or right front pillar (depending on the coupling involved), near the door cable duct. Door coupling D030 is located behind the body computer node.


The body computer node switches the front courtesy light off automatically in the following conditions:

if the door locking signal (with reference to earth C020 connector B) (central locking) is received at pin 12 connector H;
if the negative signal (with reference to earth C030), indicating the reactivation of the inertia switch I050, is no longer received at pin 14 connector G.
The body computer node also manages the switching on/off of the boot courtesy light G040. From connector G, the body computer node:

at pin 18, supplies the bulb housed inside the boot courtesy light G040;
at pin 5, receives the negative signal (with reference to earth C030) indicating the opening of the tailgate, coming from the switch on the exterior handle I033;
at pin 13, receives the signal (with reference to earth C030) indicating the incomplete closing of the tailgate, coming from the exterior handle switch I033.
Earth C020 is fastened to the floor of the passenger compartment and is located near the right front wheel arch (footwell area). Earth C030 is fastened to the left rear wheel arch (passenger compartment interior).


The opening of any of the doors (front or rear) or the tailgate is displayed by the relevant warning light in the instrument panel E050. The command to switch the warning light on is supplied via the CAN by the body computer node See E1050 CAN CONNECTION LINES . The status of the doors is only signalled in the instrument panel when the ignition is on.

Sadly it does not state the voltages.
It looks like the boot switch may well be working fine. So you now need to check the wiring, from the switch to the body, past the hinges (as above, most likely place for a break) and if necessary, identify the pin at the body computer and check for voltage there when the tailgate is opened.

A copy of eLEARN for your car may be helpful.
Here's the results of a UK Ebay search:http://www.ebay.co.uk/sch/i.html?_f...to.TRS0&_nkw=elearn+grande+punto&_sacat=36085

 

[aurick86]

portland_bill

The latch will not have a CAN module on it, it's only a switch. It does not need to communicate any other thing.
No switch will run on a voltage as low as what the OP mentioned. 0.01v is probably just his multimeter acting up.

 

[DGPunto]

@portland_bill

The latch will not have a CAN module on it, it's only a switch. It does not need to communicate any other thing.
No switch will run on a voltage as low as what the OP mentioned. 0.01v is probably just his multimeter acting up.

Agreed. I've not looked at mine but I'd expect 12v across the wiring wouldn't you?

 

[Frosty1961]

Having just repaired the same sort of issue ( my truck light was erratic but the unlocking worked just fine)...its more worthwhile to simply remove the latch assembly and check it out properly than try and delve into the Can Bus signals etc . The signals from the switch to the body computer is just that .. signals, from then on its a whole different matter.


Anyway, didn't take a lot with the latch in hand to see that the soldering to the harness plug was very poor, and a quick going over it with some fresh solder sorted the issue. I have seen a guide which has mention of replacing the microswitch, but I would do the simplest thing first

 

[g8rpi]

A change from 0.0 to 0.1 volts indicates 3 possible faults
1/ Broken wire or connection between switch and body ECU
2/ Stray ground (cut insulation) on wiring between switch and body ECU
3/ Faulty body ECU
You need to unplug the body computer and check the continuity (resistance) between the ECU connector and the switch and resistance to ground.

Robert G8RPI.

 

[portland_bill]

A change from 0.0 to 0.1 volts indicates 3 possible faults
1/ Broken wire or connection between switch and body ECU
2/ Stray ground (cut insulation) on wiring between switch and body ECU
3/ Faulty body ECU
You need to unplug the body computer and check the continuity (resistance) between the ECU connector and the switch and resistance to ground.

Robert G8RPI.

I think this was 0.1v at the switch. Possibly just a dirty switch, or poor connection at the switch wiring. Poor switches seem to be a feature on 500 and Panda, so why not Punto too.

 

[g8rpi]

I think this was 0.1v at the switch. Possibly just a dirty switch, or poor connection at the switch wiring. Poor switches seem to be a feature on 500 and Panda, so why not Punto too.

A switch can provide either a ground or 12V when closed and the opposite when open.Ground closed seems the more common and in this case there is a resistor (or other current soure) in the ECU that "pulls-up" the line to 12V when the switch is open. I've assumed, from voltages measured and lack of a circuit that this is the Punto design. While a dirty switch could give 0V and 0.1V on a switched 12V system the typical resistances make it less likely. The way to tell is to measure the measure the resistance across the switch with at least one end disconnected or measure the voltage to ground at each end of the switch with power on.

Robert G8RPI.

 

[anyzunstudios]

A change from 0.0 to 0.1 volts indicates 3 possible faults
1/ Broken wire or connection between switch and body ECU
2/ Stray ground (cut insulation) on wiring between switch and body ECU
3/ Faulty body ECU
You need to unplug the body computer and check the continuity (resistance) between the ECU connector and the switch and resistance to ground.

Robert G8RPI.

How can I do that? I mean, disconnect body computer and test it? Do I need an OBDII Adapter for Body Computer testing? Thanks!

 

[g8rpi]

How can I do that? I mean, disconnect body computer and test it? Do I need an OBDII Adapter for Body Computer testing? Thanks!

Hi,
No nothing complicated, or OBD, Just unplug the body ECU and do some tests on the wiring, not the ECU.
You will have to look at the wiring daigrams to see which pin is connected to the door latch switch. Firsteasy check is to measure resistence between ground and athe pin on th ECU connector (wiring side) with the door open and closed. It shouls read low resistance (< 2 ohms) in one state and high resistance (>10 kilohms) in the other. If it is perminantly low you have a broken switch or short to ground on the cable. If it's perminantly high you have a bad connection or broken switch.
If it's working you may have a faulty ECU.

Robert G8RPI

 

[anyzunstudios]

Hi,
No nothing complicated, or OBD, Just unplug the body ECU and do some tests on the wiring, not the ECU.
You will have to look at the wiring daigrams to see which pin is connected to the door latch switch. Firsteasy check is to measure resistence between ground and athe pin on th ECU connector (wiring side) with the door open and closed. It shouls read low resistance (< 2 ohms) in one state and high resistance (>10 kilohms) in the other. If it is perminantly low you have a broken switch or short to ground on the cable. If it's perminantly high you have a bad connection or broken switch.
If it's working you may have a faulty ECU.

Robert G8RPI

Ok Thank you a lot! But, where is the body ECU? It is inside the hood? If It is, It has a few plugs, what plug/node is it? Thanks in advance!

 

[portland_bill]

Body ECU is most likely to be under the dash, behind the fuse box.
Ideally, get a copy of eLearn to identify which pin goes where, and location of ECU. Without that, there's a lot of guesswork, which we need to avoid.

 

[anyzunstudios]

Body ECU is most likely to be under the dash, behind the fuse box.
Ideally, get a copy of eLearn to identify which pin goes where, and location of ECU. Without that, there's a lot of guesswork, which we need to avoid.

Ok Thanks a lot! I have a copy of eLearn, so tomorrow I will check it out!

 

[anyzunstudios]

Body ECU is most likely to be under the dash, behind the fuse box.
Ideally, get a copy of eLearn to identify which pin goes where, and location of ECU. Without that, there's a lot of guesswork, which we need to avoid.

After few months, finally I got my trunk working. The problem was in lock switch, I replaced it with other lock from a crashed Fiat EVO and now works like charm, and lock is even smoother when closes and opens than previous one! hahaha Thanks!

 

[swedgrande]

Hello folks,
I am going to add my wee story of non working boot latch and see if anyone can help.
One day the mechanism didn't work , so I bought a second hand one and it still didn‘t operate , I did notice though that the boot light would fade if I moved the rubber protective cable housing so I removed it and it looked like a rat had eaten its way through the cabling. The black and yellow(thin) wire was cut and the thick wires were on their way to failure. I fixed them all and still the locking mechanism didn't work. So now it was time for some voltmeter work. The 4 pin plug to the boot latch has four cables going to it. A white , black, yellow and black and yellow and gray. The yellow and black one is the cable for the boot light . The yellow and gray cable is the signal cable from the ECU (I assume) to activate the solenoid.
Without pressing the boot lease button the voltage between the G&Y cable and ground varies a little over time from 0.15 to 0.25 volts and once the boot release switch is activated , the voltage rises between 5 and 7.8 volts for a period then drops back to the initial voltage. The solenoid requires 12 volts to operate. (I connected the boot latch outlets 2 & 4 to 12 volts and it worked).
I have checked this signal voltage a two places in the circuit, one at the boot to body rubber grommet and then after removing the trim and at around the back passengers seat . Same voltages there too.

My question is , why the signal is low and not reaching 12 volts ? I have had the same issue with a signal of approx 7 volts in the passenger elec window so it couldn't be used ......

Has anyone solved this problem before ? Any help is appreciated

 

[Bernievarian]

Hej do,

looks like a resistance in the circuit for both case... I'd suspect a bad grounding.

MvH, Bernie