Another intermittent Central Locking fault

Every now and then, my central locking doesn't work, and the engine is immobilised. When this happens, it has the following symptoms:

• The drivers door unlocks manually with the key or pulling the interior lock tab up.
• The central locking doesn't fire on any of the other 3 doors when you unlock the drivers door with the key or the interior lock tab.
• The remote keyfob doesn't work
• The engine won't start ("Engine Disabled - press remote Keyfob")
• With the drivers door open, turning the key in the lock registers the key turn (beeps, and dash warns that the door is open), but doesn't fire the central locking

Usually when this happens, I slam the door a couple of times, lock and unlock using the key repeatedly until I hear the central locking fire, then everything is ok again until next time.


Very occasionally, when it's really playing up, I just sit in the car, and every now and then move the lock latch on the drivers door - at some point it will randomly spring in to life, fire the central locking, after which point I can press the keyfob and start the engine.


Also the locks "bounce" occasionally when I'm driving - I had always assumed this was the RF receiver, but I've recently changed it for the latest version (vast improvement!), but still occasionally have the locks randomly lock and unlock themselves when I'm driving.


Does this sound like a BECM issue? Seems to me like there could be some dry joint, or a cracked track on a PCB somewhere, but I'm not sure where to start looking.


It's been one of these things that I've been meaning to take a proper look at for ages, but the other day I was stuck in Tesco car park for 40 minutes, and even resorted to calling the AA. Naturally, the minute they turned up, everything decided to work again, but that was the first time it's stopped working for that length of time, so I want to get to the bottom of it rather than become stranded again!


Any ideas gratefully received.

Bad connection on lock multiplug, broken wire, or duff microswitchs in lock mechanism by the sounds of it.

tony2 said:

Bad connection on lock multiplug, broken wire, or duff microswitchs in lock mechanism by the sounds of it.

Click to expand...

+1 on that and the tailgate can cause lock bounce and other strange happenings.

Why would a dodgy lock multiplug stop the RF working, or stop the central locking from working altogether and immobilise the engine, rather than just affect one door - bearing in mind the lock microswitches register, even when the central locking doesn't and the engine is immobilised?

I vaguely remember someone posting a circuit diagram of the locking system on here a while back, but I couldn't find it when I tried searching.

Endeleus said:

Why would a dodgy lock multiplug stop the RF working, or stop the central locking from working altogether, rather that just on one door, bearing in mind the lock microswitches register, even when the central locking doesn't and the engine is immobilised?

I vaguely remember someone posting a circuit diagram of the locking system on here a while back, but I couldn't find it when I tried searching.

Click to expand...

If the drivers door does not unlock neither will the tailgate from memory. The problem will be with the actuator motor on the drivers door lock or, slightly less likely a broken wire where the loom flexes between the A post and the door or a connection problem at the outstation in the door.

Datatek said:

If the drivers door does not unlock neither will the tailgate from memory. The problem will be with the actuator motor on the drivers door lock or, slightly less likely a broken wire where the loom flexes between the A post and the door or a connection problem at the outstation in the door.

Click to expand...

I can follow the logic there - but even if the doors don't physically unlock, why would the keyfob stop working and the engine be imobilised at the same time?

It's probably worth noting that I don't usually lock the car overnight as it's in a secure place, so the alarm / imobiliser aren't generally set when I have this issue.

I'll see if I can find that thread with the diagram of the locking system electrics.

Endeleus said:

I can follow the logic there - but even if the doors don't physically unlock, why would the keyfob stop working and the engine be imobilised at the same time?

It's probably worth noting that I don't usually lock the car overnight as it's in a secure place, so the alarm / imobiliser aren't generally set when I have this issue.

I'll see if I can find that thread with the diagram of the locking system electrics.

Click to expand...

If you lock with the FOB and unlock on the key it only unlocks the drivers door. You can lock and unlock with the key and it should work.

Ok, this is my understanding of how the security system works.
When you press the unlock button on the key fob the RF Receiver sends a signal to the BeCM, if the signal is good the BeCM sends a signal to the Drivers door lock (which controls the Central Locking) telling it to unlock the vehicle. If a unlocked signal is sent back to the BeCM it turns off the immobiliser allowing the vehicle to start.

So, your fob is probably working but the unlock signal from the BeCM is not getting to the door lock, therefor the BeCM doesn't get it's unlocked signal back and the immobiliser stays active. As far as the security system is concerned, the car is still locked so it ain't going nowhere.
Once you get the central locking to work, by playing with the sill button etc, the BeCM receives a unlocked signal and allows you to remove the immobiliser with the remote.
Hope this is of some use to you my friend.

As said, this is my understanding of the system and if I am wrong I am happy to stand corrected and learn.

I've ordered a replacement latch assy from Island today, but I'm still not convinced that could give the symptoms I'm getting.

Does anyone have a circuit diagram for the BECM?

Endeleus said:

I've ordered a replacement latch assy from Island today, but I'm still not convinced that could give the symptoms I'm getting.

Does anyone have a circuit diagram for the BECM?

Click to expand...

For the internals? No, but as it's all controlled by software and a micro processor I doubt it would help you. Things like that are rarely the BECM, usually RF receiver, door locks, out station wiring etc.
The way to fault find it is with diagnostic kit where you can force functions to check them.

Changed the door latch assembly today, so will see how that works out.

I did notice something interesting that I'd never noticed before though...

If you lock with the keyfob, but unlock with the key, you get all the symptoms I described earlier with the exception of the immobiliser:

• The drivers door unlocks manually with the key or pulling the interior lock tab up.
• The central locking doesn't fire on any of the other 3 doors when you unlock the drivers door with the key or the interior lock tab.
• The remote keyfob doesn't work

I'd probably never noticed that before, because the only time I would ever unlock with the key is when the keyfob doesn't work, so assumed that was all part of the same fault. My heart sank when the central locking didn't work, but then I started the engine with the key no problems, and the keyfob unlocked all the doors and fired the central locking.


Will be interesting to see whether swapping the door latch out has made any difference, or if I should be looking more at the RF receiver / BECM.


Shortly after I'd finished, the door locks bounced all on their own, but I convinced myself that I'd somehow bumped the keyfob in my pocket. Time will tell!