[Rassettaja]

Hi! Throwing this as a last resort if some1 has any insight to what my problem could be. Picked up a 2007 scenic for grandpa after his old one decided to lose compression. So the problem is when you press the starter you can hear 1 relay clicking but no power comes to the dashboard and the thing wont crank. OBD port is dead as in nothing wont connect to it(CLIP or general scanners). I've identified it to be the a large red one right under the dash that has a large red wire and a large yellow wire that appears to feed the passenger compartment fuse box. The car was missing the uch when I got it so I fitted one that we had laying around, this brought life to the interior electronics as expected and the central locking when using the key that was programmed to the car which the uch came from. I've checked every fuse and relay that I can find(UCP(except the relays soldered to the board), interior fuse box, battery fuses, large fuses under the ucp and the ones under the drivers seat) and everything is in working order and has power. Haven't done the light bulb test yet to see if there is a short somewhere. I've inspected pretty much every wire I can find under the dash and in the engine compartment and none of those seem damaged or melted. I've got a full set of electronics from an older model(ucp with black cover plastic where as this one is white) with all the modules and wiring harness so I could swap those in and make it run with them but Id rather not go through that whole process 😅. Any tips are appreciated!

 

[ours2012]

Sorry not understanding here
You have fitted a second hand UCH, and you are expecting the car to start with the donor UCH and donor key card
If this works It will be a first

This is an analogy of how the system works
Lots more involved
You insert key card, key card sends a signal to UCH,,,, UCH then sends a signal to the steering lock, steering lock then sends a signal, back to the UCH, Uch then sends a signal back to the steering lock, to unlock the steering
The steering lock then sends a signal back to the UCH, the UCH then sends a signal to the UPC, if this is happy with this signal ( IMMO code ) It then unlocks the UPC, and this sends a signal to the ECU to allow starting

You need a full ECU kit
As in UCH ecu and steering lock plus at least 1 working key card, all off the same car

 

[Rassettaja]

Im not expecting the car to start, just to get the "ignition"(power to the dash, can bus etc) on. Also when you fit a 2nd hand unvirginized box (ucp uch steering lock ecu etc) it will let the car start up once. I can prove this if u really want. I've worked on these a bunch before(3 megane 2's and 3 scenic 2's) all with electrical issues thus i've done quite a bit of experimenting. The first megane 2 that we got came from a shop that had for whatever reason mix matched the ecu's and they told us they got it started once. After figuring out what piece belonged to which set it turned out to be a bad steering lock that functioned when ever it wanted. After prying that open I figured out that if u remove the small motor in it u can "emulate" the locking and unlocking of the wheel by turning the white part with a magnet on it from 1 side to the other. Actually drove that thing like that for quite a while. I tested the same donor uch with the donor keycard on the other scenic with no compression and it cranked once (no start obv) and i got the dash to come on and the can bus was working so that i could connect my scanner. I could also take the key out, turn the power off and on again with the same donor uch, but it wouldn't crank again. I don't see a reason to get a kit before i know whats wrong since if there is a short there is a good chance one of the control units is fried and it would just do the same to the new parts. Any other ideas?

 

[ours2012]

You dont have power to the UCH is this what your saying
Am lost here
This red and yellow wired plug, what does this go to,

 

[Rassettaja]

I dont have power to the dash and can bus. The red and yellow wired plug has a relay(the one that's clicking when you press the start button). The red wire has +12v constantly and the yellow wire goes back into the wiring harness. This appears to feed the relays and some fuses in the passenger compartment fuse box. I currently have power to all the other interior electronics. Locks, horn, interior lights, power windows, the middle console(the locking mechanism idk what to call it), ac & rear window heater indicator and the radio. Maybe heated seats haven't tested them yet. Nothing else that I know of. Can bus and dash are dead. Found a few threads online with similar issues and they both had an issue with the large red power wire in the grey connector under the drivers seat. I have +12v there and the wire on the other side of the connector looks fine, its not shorted to ground either.

 

[ours2012]

Sure dash is not dead here ?
Yours must have the black and white fuse box under the bonnet lid then

Throw your oval [plate on, will get the wiring diagram up

This wire ( Red and Yellow ) its coming from under the bonnet and going in the car ( Or the loom that this is inside is )

 

[Rassettaja]

Throw your oval [plate on, will get the wiring diagram up

Wdym by this?
Yes the red and yellow wire come from the loom that come from the engine bay.
Not 100% on the dash can test tomorrow. Immobilizer led is blinking.

 

[ours2012]

Sticker that you see when you open the drivers door, on the B pillar

 

[Rassettaja]

Dash confirmed working on other car, here is the sticker

 

[ours2012]

K4M766 is your engine code
Bet your wondering why I have put this

 

[Rassettaja]

Update! Car is started! 😊 Problem was blown elecetronic ebrake module! Got new ecu set for the car -> no change in behavior. Did some googling on how to reset my lagunas ebrake and by chance found someone who tried to reset theirs and it killed their scenic, same exact issue as we have. -> Found blown fuse for "automatic parking brake" under drivers seat -> replaced it -> blows immediately -> unplug ebrake module -> replace fuse -> car starts. Hopefully this can help someone else. Absolutely stupid imo that something labeled "Fuse for automatic parking brake" can immobilize the whole car.