Can someone point me in the direction of a circuit diagram for a Discovery 300 Tdi OEM alarm please.

My Haynes doesn't cover this item. Many thanks.

What aspect of the alarm are you wanting to look at in particular, I have no plans but can help with some problems with the alarm/immobilser problems as have had to deal with these myself.

Hi, Thanks for your response.

I have some problems with my Daughters 300Tdi which I have traced to the alarm.

Someone at sometime has by-passed the diesel shut-off valve by connecting it up to the ignition supply direct.

There was a fault on the locking also and that I traced back to the drivers door motor.

Having fixed that, the original shut off valve wiring was operating again and whilst I was running the engine to warm up to test the temp Gauge after replacing a thermostat, the engine cut out after 20 mins and I cant get it started again.

I am sure that this can be attributed to the alarm module, which I now intend to remove and replace with a Clifford alarm.

I am a trained auto electrician and would no doubt be able to work it out but a wiring diagram would be a big help and time saver.

Regards,
Brian.

Hi, the alarm and immobilisor are two different units. The immobilisor is operated by the main ECU and can be turned on or off by a LR dealer. If it's switched on which it sounds like it is then it operates automatically every time the ignition is turned off and the fob removed from near the proximity sensor. It needs the fob to be next to the sensor to disarm it so if it was not working before this might explain why the circuit was by-passed. The immobilisor circuit can easily be worked out from the Haynes manual as I used it to work out my system however it doesn't show the circuits inside the ECU. If you haven't got a working fob for the ignition them you either need to get one and have it coded (about £75) or have the circuit disarmed by a dealer (again about £75). Note: The sensor coil is fitted behind the ignition key bezel.

Hi Don,

Thanks for that.

I managed to find the cause of the problem. Dry solder joints on the unit under the radio and fixed to the top of the heater casing. I have seen this described as the "spider" This is in fact the immobilser.

I had to remove the whole center dash section to get to it so I assume this is why the stealer's charge is £75 for fitting the shorting plug that by-passes it.

Having repaired the PCB and got it working again, I moved the unit to a more accessible location next to the steering column (the wires are long enough to do this) so when I need to get to it again I wont have to disassemble the dash.

I also found a fault on the alarm module (located under the glove box) which now works again.

I was somewhat confused as to how the reader on the ignition lock worked as most cars use a passive RFID transponder fixed in the key whereas this appears to be a powered device inside the remote control, and uses its battery.

The receiver for the remote control is contained within the alarm module. So presumably if you loose a remote the need to have both the alarm and the immobilser module recoded is the reason for the high cost involved.

Phase ii of this will be to remove the whole lot and replace it with a Clifford alarm with 3 point immobilser. The existing wires in both the alarm and the immobilser make this relatively simple.

That however, is for another day.

Thanks for your help.

Hi,
I have problems with my Disco and have had the car at landrover for three months and they cannot help me. I would like to ask you the question directly.My Email is desavigny at gmail.com
I would appreciate if you ahve time to respond.

abutoma said:

Hi,
I have problems with my Disco and have had the car at landrover for three months and they cannot help me. I would like to ask you the question directly.My Email is desavigny at gmail.com
I would appreciate if you ahve time to respond.

Click to expand...

Good Lord, 3 months ? and they have access to the circuit diagrams. It took me 3 hours to sort it out without any diagrams. Its not really that complicated once you understand how the tree key elements are integrated.

I would have thought that given the fact it can only be one of two modules and the remote control that are defective, they must be able to substitute proven units to find the problem.

All systems after the modules are straight forward wiring, goodness knows what they would do if they had to deal with can-bus.

I would be happy to help if I can but I am a busy person at the moment.

Where are you in the country ?

Unfortunately I am in Norway!
I know electronics and electrotechnics (certified)
The symptoms are that if the central locking system is working then everything is OK. But if the remote fails to open the door then I cannot start the engine (the blocking is working) This fault is intermittent.
To me it sounds like it is the receiver for the remote radio signal is not reaching or not been "developed" by the central locking system.
They say they have tried to exchange the spider unit etc, but nothing works.

To me it is a problem of not daring to use the Disco since I may be stranded wherever I am parking. (In a parking lot that could be expensive)
So I want to route the +12 to the solenoid to crank the engine and to the diesel pump through an auxiliary switch for use in "emergencies" But they said they did not know how to do this.
I have got the Disco home now but it is snow and cold being outside trying to find the way to do it.
So I just wonder if that can be done from the alarm unit's relays in the footwell or if I have to rip out the mid console to the spider.
They have even, thy said, ordered this "shortcircuit" plug in for the spider, but have not received it.
I am exhausted.'
Any hint for the auxilliary switch arrangement?

From what you say, it sound to me like a break down in the RF link between the remote transmitter and the alarm module.

I have noticed that the remote transmitter is very sensitive to low battery voltage. Anything less than 3v on load and the range drops off significantly.

Because the transmitter has a rolling code generator, you can get the situation where you press once, which generates a valid signal but this is not received by the alarm unit because it is too weak or you are too far away from the receiver, then the next press is out of sequence with the rolling code generated.

As it takes 3 presses to re-establish the sequence, as you become frustrated, the problem is compounded.

Thus your description "But if the remote fails to open the door then I cannot start the engine (the blocking is working) This fault is intermittent."

The remote operates the alarm, the alarm operates the locking module and the locking module powers up the tag reader in the steering column and if the correct tag is present the immobilser (spider) is released and you can start the car.


If your car is the standard Diesel arrangement as opposed to the electronic EDC version, then you will have to pull the spider out even if you intend to "hot wire" the circuits.

My advice would be to check the key fob, especially the battery contacts for dry joints, re-solder them anyway, and fit a fresh CR2032 battery cell.

Check the cell voltage before inserting it, it should be at least 3.3 volts off load.

Re-establish the rolling code sequence by standing as close the alarm module as you can (not sure where it is on LHD cars) and pressing the lock button three times, that should re set it.

If the locking has got out of sequence with all this messing about, simply use the key to re-synchronize it.

As another thought, make sure the cars battery is fully charged as this can have an effect on the RF receiver board inside the alarm module.

If your car has EDC, sorry I haven't figured that out yet.

Good luck, if you lived in Spain or Portugal I would offer to come and sort it out for you, but Norway is a bit too cold for me.

Thanks for a quick response. Yes, I agree it looks like the Rf receiver in the car is not receiving the fob signal. I have got a replacement instruction for the antenna on the alarm module. It seems to be a rather simple thing so I will try that. But still the anxiety being afraid of being stranded prevents me from using the car.
Somebody on the Internet gave me an instruction on which terminal on the alarm module that could be earthed and that would enable me to start the engine. At that time I just threw it away as I trusted that Landrover would fix the problem for me. Now of course I cannot find back to the advice.
It would be working because the tag reader can read my fob.
Any idea?

Yes, I understand the temperature concern. But this summer it will be nice and I am afraid the car will still be just standing there.

I would be interested in reading what they have recommended in the replacement antenna service document, could you possible post it up please.

I don't know off hand which pin on the alarm will give the desired result, thats why I started this thread in order to find a circuit diagram.

If you can get the system to work, you could use the key to lock and unlock when you use the car if you are concerned about getting stranded.

The Technical Information sheet does not say much.
The replacement antenna is AMR2034A-96 MY Antenna, Alarm System
Instruction for replacement:
Remove yellow wire and terminal fromC225, cavity#26
The antenna to be place between the glass and the dashboard and reconnected to C225
The bare ends of the yellow wire does not need to be insulated.
I have the block diagram for the theft alarm but not the circuit diagram. This is the one they have at Landrover.

-------
Yes, if I only could fool the theft alarm the key would do it

If you are interested I can scan and send you the lot. There are 25 pages

abutoma said:

If you are interested I can scan and send you the lot. There are 25 pages

Click to expand...

If thats not too much to ask, I would be very grateful, thanks.

But I am not sure that it is a good idea to put in on the Inet
Do you have a private account?

abutoma said:

But I am not sure that it is a good idea to put in on the Inet
Do you have a private account?

Click to expand...

Sure, I will PM it to you.

Thanks very much for the schematics.

I think I have got the full picture now.

This would appear to be how the system should work on the
Discovery 300 TDi. (Non-EDC version)

The petrol engine variants and the automatic are very slightly different as is the EDC equipped Tdi

There are only 4 modules for the security system, Main alarm processor, Immobilser, Siren and Code reader ring.

The alarm processor is located under the glove box on the RHD models, and contains the central locking control, the code reader decoder, and a crash switch. (Diesel only)

The siren is battery backed up and is located under the bonnet.
The immobilser (spider) is under the radio behind the dash.
The code reader is next to the ignition key lock.

Assuming everything is working and starting with a locked and alarmed vehicle.

Pressing the unlock button on the remote signals the alarm to switch off and the central locking to open. The turn indicators flash to confirm.

Placing the key in the ignition will allow the code reader ring to interrogate the transponder inside the remote. This in turn signals the spider to allow supply to flow to the diesel stop valve and the starter relay. (On the petrol models it’s the fuel pump and 15+ terminal on the coil) the engine will now crank and start.

When the ignition is turned off the spider will power down and the alarm will remain in standby mode for as long as the keys are in the ignition.

When the keys are removed and the remote is out of range of the code reader, the spider times out and locks up.

When exiting the vehicle and pressing the lock button on the remote, the alarm is set, the locks are closed and the indicator flash to confirm.

There is a crash switch inside the alarm control module which is designed to activate in the event of a crash, it signals the door locks to open, and triggers the spider to shut off the diesel stop valve (it also inhibits the starter relay) and activates the hazard lights.
NOTE: the petrol engine vehicles have an external crash switch which is mounted under the bonnet behind the washer bottle and shuts off the high pressure fuel pump as well as opening the locks and activating the hazard lights)

All of the above is obvious to anyone who owns or has used a Disco but I thought it was worth going over it before looking at the problems that can occur.

The things that seem to fail are, the remote control, [low battery, broken contacts, dry joints.]

The alarm module can also suffer from dry joints and water ingress. The spider seems to be very prone to dry joints and burn outs (imho the PCB and relays are not rated correctly for the job)

The siren module can also be subject to water ingress.

The steering lock code reader simply a copper wire coil and shouldn’t fail in normal use.

If you can’t unlock the car with the remote, you are in trouble as everything else depends on this.

It is relatively easy to by-pass the spider once you get to it.

The wires are all black but the terminals are numbered. 1 – 10
There are 2 live feeds both from fuse 3 in the satellite1 fuse box under the driver’s side dash. On the Tdi this should be rated at 30 amps. (The MFI and V8, 10amps.)

Only 7 of the 10 terminals are used on this unit.

It is relatively easy to by-pass this module but its probably unwise to say how on an open forum. Land Rover can supply a shorting plug, I don’t know the part No. or price.

What I have learned is, that it would be a very simple job to rip out the alarm module and replace it with an aftermarket alarm, which can be hooked up to the existing wires at the OEM alarm module and at the spider to provide the immobilser function.
This is exactly what I intend to do with my Daughters 300Tdi

I have decided to fit a Clifford alarm which has a 3 point immobilser 2 radio keys and will work with the |Discos central locking, dash LED and connect to the spiders wiring…the price…. £55. Twenty quid cheaper than a single unprogrammed remote control from LR

The only thing that wont work is the central locking from the key in the driver’s door, but I can fix that with two Bosch 5 pin relays at a cost of £3.

I will work up a coloured wire for wire connection chart while I am fitting it and if anyone wants a copy I can PM it. But please wait till I’ve done the job.

Abutoma, I will PM the shorting instructions for the spider then you can drive your car again.

This is the Landrover by-pass plug. £5.24 inc. VAT

Thank you for all assistance.
I have not yet been able to try things out since the outside temperature is still hovering around 7-10 minus degrees, and we have 10-15 com snow on the ground.
Will keep you informed