Central locking issue

Hi Chaps,

Got a problem with the central locking. Occationally, when I open the car using the squeaker, I get the indicator flash but the doors don't unlock. The back door will open but the solenoids to mechanically unlock the side doors don't even click. If I unlock the drivers door with the key, then switch on the ignition, then close the drivers door then the other doors unlock. This only happens occationally but has occurred twice in as many days recently.

So I'm looking into the circuit design in Haynes and I note that the CCU controls central locking but on the L series it doesn't handle security. The indicator flash is controlled by the hazard relay which is part of the CCU. Therefore the security system is talking to the CCU.

So why don't the doors unlock?

So, I got round to doing something I've been meaning to do for a long time. I download the Rave manual. This was even more bizzare as it doesn't show the security system at all, not even the RF receiver.

I have had a couple of low squeaker battery alarms recently so I'll get a new battery fitted and see if that improves the situation.

In the meantime, has anyone else had this or know where the problem might be?

Cheers,

Dave

Well, last night it took the next step. Now it won't unlock whatever I do.

So this morning an investigation began. Results. It is clear that the CCU is generating the unlock signal because the relays inside the CCU are clicking. However, no doors unlock. This is significant because of the option that the drivers door can be opened first (switch off on mine) so there are two unlock circuits, one for the drivers door and the other for the other three side doors.

I intercepted one of these circuits and there is no voltage on it when the relay operates.

Now, the power supply to the CCU to unlock the doors is via Fuse 15. This fuse is intacted. I even changed it anyway. I knew I was clutching at straws as there is one significant flaw in the power supply plan and that is the lock signal does work.

So I have two relays that don't appear to be switching any power, yet the power feed is present to the CCU. Therefore the problem is inside the CCU.

SO, out came the CCU and with four screw drivers, off came the cover. Great, custom electronic packages and non-standard relays. All back together, jst on the off chance this had fixed the problem, but no.

Oh well, looks like a new CCU then, and thats a stealer job to set it up.

This is going to be one of those

:violent: FREELANDER

days.

Well, I'm talking to myself and I feel this is because no one really knows the answer to this one. Earlier, a very depressed Darmain made his way to the recycling centre (not to recycle the Hippo, well not yet anyway) and driving along I found time for thought.

Donning my professional hat of electronis system engineering I considered what the problem was with this extremely annoying CCU and what I could do that didn't involve spending something like £300 on a new one and another £200 from the programming at the Stealers. After all, all the other functions are operating okay.

So, heres my plan, as it will stand, or fall. My options are:

1. Repair current CCU.
2. Rig an unlock switch on dashboard to release other three doors, after using key to get into drivers door.
3. New CCU.

Then another thought occurred to me. This problem wasn't new at all, it had always been there. I have always had problems with random doors not unlocking and requiring a second squeeze of the squeaker to get full access, this included the drivers door. I had assumed this was due to mechanical drag. However, recently I had a problem with one rear door that refused to unlock, even though it could be heard to do so. This turned out to be a lubrication problem. With that fixed, this door still suffered with an unreliability to unlock.

So discounting mechnical drag now what could be left? The answer is too low a voltage on the unlock signal.

I considered the design of the CCU as if I was designing it. Now if the job was done properley there would be overcurrent protection on the solenoid circuits, built within the CCU. The 20A fuse is the last line of defence really. Of course a normal rupture fuse is totally impractical in this design as it would be buried deep in a black box and not accessable. The alternative is a self healing fuse, which is better known as a thermistor. Basically the device carries the current to the load. If the current gets too great then the device self heats, this increases it internal resistance and this reduces the current flow. If this device breaks down then it will assume a higher resistance permenantly. This will reduce the voltage available to the lock solenoids which will slow their operation time. This failure mode will cause the device to overheat, accelerating its failure, until eventually it goes open circuit and no unlock.

This theory fits for a number of reasons -

1. The main fuse is intact.
2. The lock signal works (Different device)
3. Both the drivers door and other doors failed at the same time, which means two relays are affected, the chances of a double relay failure at the same time seems highly unlikely.
4. The unlock signal gets used many more times than the lock signal. This is because of the cars annoying habit to signal unlock when the ignition is switched on, or when the drivers door is shut with the ignition turned on. Therefore greater chance of failure.

I reacon that CCU is come out again for a bit of a closer inspection and test. The question is can I drive the car without it???? Reacon I can, if the imobiliser doesn't fail safe.......

More, I suspect to follow. Its a rambling but it might be useful to someone else.

Posting just to let you know your not talking to yourself. I haven't a clue whether your reasoning will turn into a fix but I wish you luck.

Thanks Chaser. The unit it still in the car while I pluck up courage to brave the freezing nights air to go and get it out.

Well, further investigations. The connector into the side of the CCU can see the lock solenoids and they are all alive and well. So far the theory is proving itself. Now I am bloody cold and tired and the next step can wait until tomorrow.

its a funny thing is central locking and i'm having trouble with mine. I can push the knob down on top of the door and it will close all though the back one doesnt. I have no key fob and only one key. Any body got any suggestions or am i dealing with the same problem as you Darmain.

Right, CCU out of the car and on the table. Covers are off.

First news is that the car doesn't run without this box. The imobiliser has failed safe. better not blow this thing up then!

Second news is the locks do not work as I suspected. There are two solenoids in each lock, but one is for lock / unlock and the second is for superlocking. Thats knocked my theory on the head, except for the fact that the CCU is at fault and I definately know the locks are okay now as they do lock.

The unit uses a cheeky NEC, dual relay component, so on initial inspection it looked like three relays where is is infact six. One of them is configured as a change over switch, so I'm guessing thats the lock / unlock selector.

I am continuing to reverse engineer the design and will report later.

landy93 said:

its a funny thing is central locking and i'm having trouble with mine. I can push the knob down on top of the door and it will close all though the back one doesnt. I have no key fob and only one key. Any body got any suggestions or am i dealing with the same problem as you Darmain.

Click to expand...

If all doors lock and unlock on the key in the drivers door then all is well with this aspect of the CCU.

Okay, update time.

Here is said CCU unit.



Got the back off using four screwdrivers as before.



and revealed the component side.



Trying to reverse enginer the design got a bit difficult without depopulating the PCB, and I wasn't going to do that. So I rigged up a power supply of 6VDC, which is what the relays are driven by and went round each coil, while testing for the operation. One didn't operate, RL2.

So, fired up the soldering iron and out it came.



Here's the little begger.



Now I've got to find another, which is proving a bit of a problem as I can find no distributor for NEC components who is likely to be interested in a single quantity sale and nor can I find an alternative with the same footprint.

Now I happen to know this guy at work whos rather good at this sort of challenge.....

Now for the final update of today. Having got the relay out I was able to determine the function that the two segemnts of this component performed. It seems the faulty side is reponsible for switching the Ground connection of the solenoids to either Positive or Negitive, depending on the action required. It obviuosly couldn't change state, which resulted in a total loss of the unlock function. The other side of the component handled the superlock control.

Then a devious plan hatched in my mind. If I could swap the functions then I could lock and unlock but no superlock (no big deal).

The easy way was to fit the relay back into the card backwards. A great plan but the pin out was not completely symmetric, so that wasn't going to work.

So, take said relay, bend the asymmetric pins and solder on a bit of wire to each.



Now two layers of insulation tape over them.



Now thake the card and mask the two asymmetric barrels, also with two layers of insulation tape.



Now fit relay but not tight to the board. Tack solder the pins, as I want to get this out when I get a new relay. Now bring the two wires over from the component side and solder them to the empty barrels, remembering to cross them.



Please escuse my soldering, I didn't want to get the board too hot as I will need to get this out again and too much heat will damage the PCB.

Put it back in the box, then fit it to the car. Cross fingers and reconnect the battery.

Guess what, it worked!! Yippeeeee!!!!

But as they say, every silver lining has a cloud.

One thing I read on RAVE was that the internal lock control switch was inhibited by the operation of the inertia switch. My internal switch has never worked, so while in the engine bay I saw the switch and playfully pressed it.

CLICK!!!

WTF!!

So, what exactly happened to trip my crash sensor, before I owned the car!!!?????

Oh well, works even better now.

:5bparty:

:beer2:

Well done thet man!!
The inertia switches are a law unto themselves. Have a Rover K series that was going all right and I read about the inertia switch and just had to have a push. Bout a week later at 60 down the dual carriagway it cut out. Pulled over reset it and it's not done it again in 3 years? Try not to hit anything hard enough to test it properly.
Now you have found the problem relay - can you source a DEAD CCU - chances are that one of the three relays will be a good un'.

Electronic engineer methinks, handy to know - do you ever look at the Range Rover forum?

hippolover said:

Electronic engineer methinks, handy to know - do you ever look at the Range Rover forum?

Click to expand...

Can't say I do look at the Rangy forum, would you be referring to the P38 per chance? I went to the Motor show at the NEC the year the P38 was lanched. During the presentation, which had a vehical being assembled in front of our eyes, so we could see the transmission, they mentioned that the switch panel on the drivers door was so complex that if you had descete wired it then the door would never move due to the thickness of the wire loom. As a result they had used a telemetry interface, which I assume was CANBUS. plenty to keep the techies scratching their heads.

I am an Electronics system engineer and work in the railway industry. Our systems also use CANBUS because it is very rugidised in electrically noisy enviroments, such as next to a sparking catinery. Last week I got hold of a new CANAlyser, which allows you to view, control and diagnose CAN systems using a PC. This kit cost the company 7 grand, glad I didn't have to pay for it. Most of that was for the sofware license.

P38, got it in one.

Some good, some bad, all fickle - kind of a cross between a three year old child and a constipated elephant. One wants or doesn't want to do as it pleases for the sake of it and the other just simply doesn't go!!

We have two here (P38s) plus a Classic and a Freelander.

Well done Darmain, not many people would have the b******s to try such an intrusive fix.

I think the nec is a 'H' bridge relay. If so the
IMO EN2B3N1S is an equivalent and looks like the pin configuration is the same.
Picker PC566 is a 'H' bridge but with a different pin out.
Tyco also make them.
So far I can't find anyone who sells them though!!!!!.

try Mark5 - Obsolete electronic components - Relays

Kin Ell!
Least it's the 3L1ST @ £17 not the 3L1S @ £28!
Even at £17 I'd have the top off and see if the contacts can be fixed, the armature must work if it still functions with your swap round?
Best of luck.

Well, I have to say that I haven't investigated any further into finding a replacement as to yet. mainly because works been nuts and my little girls been quite poorly this last week and Hippo's been behaving himself.

However, I see some of you have. Thanks for that chaps. Do we have other electronics engineers here or just a healthy interest?

TD John, you mention prices. Where did you find these?

As to getting the top off, it did cross my mind, but as the relay is a sealed design I would have to attack it with the dremmal (Its potted so I'd have to slice the top off). the risk was a totally knacked relay and as I don't have a replacement yet...

Of course another solution is to bread board a functionally equivalent design using two generic class C relays, mount it on the back of the case and then link it to the mainboard using link wires. It may come to that if it fails again and I haven't sourced a direct replacement component.

Many thanks,

Dave