Hi Friends,

After searching around here for some time, I don't believe anyone has posted about this particular one in a way I can find it.

This is my 2002 VDP, 105k miles. Suddenly the door locks lost power and the trunk latch will not operate by power. (I can get into the trunk via the mechanical key.) Cabin trunk release button does not work; door lock button in the center console does nothing - everything is in manual operation at the moment.
Thinking first of fuses, I checked the door lock actuator fuse (number 2) in the RH rear seat foot well and found it to be intact. Then I moved to the Security Locking and Control module fuses in the trunk. I found that fuse #10 (10 amp) was blown. After replacing, I heard power locks click and then power was out again - fuse blown again. I repeated replacing it one more time with the battery disconnected, in case the immediate power surge to the module may have been at fault, but again the fuse blew immediately.
According to the handbook, Fuse #10 in the trunk is officially labeled "Security and locking control module (luggage compartment release, caravan/trailer direction indicators, fuel filler flap relay)." Doesn't mention the door locks.

So it seems to me that the SCM is working since I get that initial moment of life the moment the fuse is replaced. Does anyone know where to begin troubleshooting this circuit and what to do?

Thank you as always for the time you selflessly put in to help me,
Garrison

 

I would start at the SCLM. Remove it and clean the connector plug and the module connections. Use electronic cleaner and a brass type brush.
The SCLM is mounted beneath the fuse box in the boot right next to the battery. Before doing in disconnecting make sure the battery is disconnected.
While you are in there check the battery vent tub and make sure it is (a) connected, (b) has no breaks and (c) extends thru the exterior of the boot.
A poorly vented battery can cause all kinds of corrosion to things in the boot.

 

The power supply to the SLCM comes from the fuse #10 that you said is blowing. There are three outputs from the SLCM: one to the Fuel Flap lock relay, one to the Fuel Flap unlock relay and one to the Trunk Release Actuator. it is possible that one of these is faulty causing the fuse to blow.

Fuel Flap control - there are two small relays next to the trunk fuse box; take them out and try again with a new 10A fuse; if it blows again:

The fault may be in the trunk release actuator or a short in the wiring to it. To check the wiring, remove the plastic cover along the RH trunk lid arm (U shaped) and inspect the wiring inside. It is not uncommon that some of the wires there get damaged or completely broken. If you don't find any damaged wires, disconnect the trunk release actuator (under the inner trunk lid cover, next to the trunk locking latch) and then do one more try with a new 10A fuse.

Otherwise, even though the door locks are not directly operated by the SLCM, the SLCM is linked to the driver and passenger door lock actuators so, when the fuse blows (SLCM inactive) it probably also disables the door locks operation.

 

These are extremely helpful suggestions, thank you very much. I'll write back in with results.

 

I was able to test the theory about the two fuel flap relays last night, and that was not the issue - fuse still blew and in addition to that I got a small puff of smoke rising from the actual SLCM underneath the fuse box. Car still runs, thank God! I should be able to mess with the harness tonight, but before I do I will take out the module and examine the circuit board and let you know if I find anything notable.

 

In that case, the fault is in the SLCM itself but check the wiring along the right boot lid arm anyway. You will probably have to replace the SLCM and have it programmed to your car.

I once had a look inside my spare SLCM - there are 5 power components that, if any one fails, could cause the fuse to blow up. These components look like power transistors but they are actually something else. One is marked MRC71025SE and the other four MRC71024SE. They don't seem to be available and I couldn't even find their datasheets. Post a picture of the internals of your SLCM showing what has burned (if obvious).

 

Okay I will definitely post a pic when I can get it out. Last two nights have been solid thunderstorms up here after I have gotten out of work, and now I won't get another chance to pull her apart till Sunday night! Thank you so much for the detailed advice.

 

Alright sorry for the delay, it took some time to get the weather and my time to align for this project.

First, I read somewhere on the forum that the VCATS sticker from the trunk is required to find the correct replacement board. I took pictures of everything that seemed relevant to help find a replacement.

However... a couple years back I had to replace one of the little chips that controlled the right side brake light, someone on the forum had an extra and was kind enough to ship it to me. Today's burnt piece appears to be the one next to it in the middle of the three.
Do you think replacing the middle one might be all I need? I don't know that chip's part number since I didn't order it last time, so if someone knows the number it would save me from digging around. Also, I'm hesitant to think that will be my solution, because the symptoms were completely different when the other one needed to be replaced. All I was dealing with was an inoperable brake light and a cluster message "Check Rear Lights" on every brake pedal press.

Please enjoy all my pictures and let me know what you think. I'm happy to replace the entire module with the correct one if you recommend it. Thank you!


VCATS sticker from inside the trunk

The LNG2600HB seems to be the part number referenced when eBay sellers list these

FCC numbers

Burnout. The one to the right in the pic was replaced (by me) a few years ago.


Sticker on the back of the main PCB

The daughterboard

Printing on the main PCB

The tyco part numbers I think were referenced in the thread, but they do not appear to be burnt out.

 

The three "chips" are most probably all the same and they are BTS409L (as seen on one of them). It's a simple component called "Power Switch" - something like a solid state relay. It is certainly worth trying with replacing the burnt one (or all three of them). They are easily available on Ebay (BTS409L1 which is the same). Just make sure you get the version in SMD housing, like the one on the pic:

 

Ordered one tonight - thank you! I'll keep posting with results.

 

After removing my BTS409L1 to replace it, I believe I need an entirely new module. See the attached pics; part of the chip was still fused to the board when the solder came up, and when that silicon was scraped away, part of the burnt board came with it. You can see a divet in the board, and in the pic of the old chip next to the new, you can see a strip of silicon missing. The board itself had some copper strips peeling up and apparently not connected to anything - I think they had smoked the green stuff out of the board when burning up. So much for the fuse protecting the components, right?
So I did try installing the new chip, hoping for the best. You can see the pics of the new chip in place. The part that grounds to the board was correctly soldered in place even though the chip set a little higher than the original. I installed in the car and again got smoke when the fuse was installed. Fuel lock switches were clicking and the fuse instantly blew. When I pulled the module again to take a look inside, the heat from that event made the chip melt the solder perfectly and it was set right down to the board like new - funny.
At this point I tried installing it again while the board was out of its plastic box, so I could look to see anything smoking. I did not install another fuse at this point... nothing bad happened but I had already come to the conclusion that this board had had it. I still have no brake lights along with the original symptoms on locks and stuff.

Now I know that by using the pictures I posted above - especially the sticker inside the spare wheel area - someone can tell me which replacement SCLM I can buy of the variety that are available... or maybe someone has the correct one in their stash that they'd like to sell me? Please let me know if any of you can point me in the right direction. Thank you!


Part of the board is melted away - it was like black sand that crumbled away


Old chip missing some of its silicon casing

New chip in place

Sits a little high but is fully soldered in place

 

Did you check the wiring to the trunk release actuator under the plastic cover along the RH trunk lid arm? If the wiring inside is all good (no breaks or shorts), I suggest that you unplug the trunk release actuator and the two small relays for the fuel flap then try with a new fuse again. If it blows, it will confirm that the problem in the SLCM itself.

 

I did try unplugging the fuel flap relays - that was the first time I saw smoke come up from the SLCM case. I didn't mess with the trunk actuator or the lid wiring yet, but I will do that tomorrow evening and report back.
I did order an LNG2600HB from a car with a /008 code sticker, because I don't trust my board with a big chunk of silicon burnt out of it. I hope you agree with that decision. I didn't get any replies about the other contents of the trunk wheel sticker, so I didn't ask the seller about any of the other numbers.
Thank you for your continued help!

 

SOLVED thanks to your help.

I believe I did fry my SLCM with the fuel flap relays. Here's the deal:
- I checked my trunk lid wiring and it all looked and felt like new.
- Plugged in my eBay SLCM, left everything else as-is, and reconnected the battery. A new fuse 10 was still not installed. No smoke from the new SLCM (yay).
- Disconnected the battery again and added in Fuse 10. Connected battery and the fuse immediately blew.
- Disconnected the battery, unplugged the trunk latch module and took out the fuel flap relays (again).
- Connected the battery, added the fuse, and it did not blow.
- Reconnected the trunk latch module and the fuse still did not blow.

At this point, I have brake lights, trunk lid, everything except the fuel flap lock so I decided to leave well enough alone. A fuel flap lock seems like an idea left over from the 70's oil embargo to me. I'd love to take a poll of the forum to see how many people have had gas stolen by siphon in their lifetime!

Here's a tiny tidbit that others might learn from: I knew the new SCLM would require key fob reprogramming. When inside the SLCM box soldering chips, I noticed that the RF receiver is a daughterboard attached by ribbon cable to the motherboard, screwed into the lid of the SLCM box. I thought, "If I end up needing a new SLCM, maybe I can use this RF board with the new motherboard to keep from having to reprogram the fob." So I did swap them on the new module - but it did not prevent reprogramming. I guess that board handles RF reception but is not where the RF code is stored. So if you get the same idea, no need to waste your time trying it.

Thank you to all for your time and very helpful advice!

 

Great news. I don't think it matters if your fuel flap stays unlocked as nobody will know it is unlocked. If you wish to check the relays, you can either check the resistance between the pins marked with red lines on the picture (a good relay will read ~100 Ohm) or you can connect 12V to these two pins (polarity doesn't matter) and listen for the relay clicks. As there may be a short in one of the relays, connect the 12V via a car bulb (min. 5W) to avoid sparking. If the bulb does not light and the relay clicks, it is a good relay; if the bulb lights-up and the relay does not click, it is a bad relay. If the bulb does not light-up on any of the relays (irrespective of whether the relay clicks or not), then do the following test:

Connect one lead from the battery to one of the marked pins and touch each of the 3 unmarked pins with the other lead from the battery via the bulb. Then do the same with one lead from the battery connected to the other marked pin. The bulb should not light-up in any case. If it does, that relay is bad.

 

It is always great to have someone close out the issue letting us know what worked.