non usual alarm fault question?

my brother has a 1998 2.5 dse, everytime he puts the key in it says "alarm fault" (not unusual)
i swapped the sensor from his into mine ( no messages) and vice versa.
his still says "alarm fault" with mine in there,
mine has no warning message with his in there.so it cant be the ultrasonic sensor.
what else is there in the circuit? bad earth? bad connector somewhere?
is the bit underneath the clock anything to do with it? cant find any reference to it on rave.
your assistance would be most appreciated.
alan

My defender would sound its alarm when turning the ignition key, after starting it stopped sounding. Was doing it on the first start up of the day but not subsequent starts, until next day. The car battery was failing and the fault stopped after fitting a new battery. What I am getting round to is, check the battery voltage. Might be as simple as that?

brother fitted new battery when he got the car a couple of weeks ago, its the right one, ive checked
also alarm doesn't make any noises, the dashboard says "alarm fault" and interior beeper sounds, every time you put the key into the ignition.

Could be the wiring to the sensor.....

You'll probably need to get some diagnostic kit on it. The alarm/immobiliser setup on these is very complicated. Without knowing what the "alarm fault" code is, you're piddling in the wind.
It could be a bad connection at the BECM I guess, especially if you've had issues with the heater orings.

unfortunately i dont know the history of his car, all i know was that it had a lot of problems with the door locks when he got it.

If you're both planning to keep p38 for a while I'd strongly suggest buying a nanocom between you. It'll save you a fortune.

i've had mine for 17 years and only twice needed to plug into diagnostics

al-one-arm said:

i've had mine for 17 years and only twice needed to plug into diagnostics

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You've been damned lucky then!!

i broke the habit of a lifetime. never buy the first of a new model, wait till they have fixed all the teething problems then buy one, mine was 5 years old, gas converted, new engine, 112k miles. now its 191k a few advisories on mot's but nothing much gone wrong since.

I think the bit under the clock is for the HEVAC.

I'd be thinking wiring connector somewhere or maybe it thinks the door locks have been tampered with? If he's had door lock issues I'd be thinking RF interference, especially if he's had a flattened battery. Need the gen 3 receiver if there are any wireless weather stations or similar or maybe some wifi hotspots nearby.

on brothers car the door locks were having fun. firstly the passenger front door would not unlock or lock with remote or key, but would when button was pressed or lifted. changed outstation and lock( bought from ebay) still wouldn't work. then drivers door microswitch would not operate properly, kept saying door open unless you pulled it closed, changed the drivers door lock(again from ebay) that fixed that problem, tested passenger side lock by putting 12v to pink/black and ground to orange/black. no good.took the motor from the old drivers lock fitted it into passenger lock, that fixed the problems with the passenger door, it also made the puddle light work

I fixed one the other day that had ALARM FAULT on the dash - one of the pins in the connector was corroded, so removed it and replaced the connector pin.. Fault went away after that...
Diagnostics won't help a lot, as the BECM doesn't store fault codes - but it's usually either sensor or wiring from memory - and if your sensor is OK, then i'd inspect the plug/wiring.

I've also heard that the wrong setting under the alarm sounder (Klaxson vs BBUS) can cause Alarm Fault - but if nothing has been changed in the BECM diagnostically, then points back towards the ultrasonic sensor/wiring..

Bit under the clock is, as Grrrrr says to do with the HEVAC - it's the aspirator (in car) temp sensor. Has a little fan in there to draw air over the sensor. Well known for getting crudded up with dust etc.

Interesting to read this, mine does the exact same thing. Found the siren in the engine bay had been disconnected, plugged it back in and nothing, still 'ALARM FAULT' on the dash. Lights don't flash on either lock or unlock.

martyuk said:

I fixed one the other day that had ALARM FAULT on the dash - one of the pins in the connector was corroded, so removed it and replaced the connector pin.. Fault went away after that...
Diagnostics won't help a lot, as the BECM doesn't store fault codes - but it's usually either sensor or wiring from memory - and if your sensor is OK, then i'd inspect the plug/wiring.

I've also heard that the wrong setting under the alarm sounder (Klaxson vs BBUS) can cause Alarm Fault - but if nothing has been changed in the BECM diagnostically, then points back towards the ultrasonic sensor/wiring..

Bit under the clock is, as Grrrrr says to do with the HEVAC - it's the aspirator (in car) temp sensor. Has a little fan in there to draw air over the sensor. Well known for getting crudded up with dust etc.

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Marty, should it be klaxson?

P38Penguin said:

Interesting to read this, mine does the exact same thing. Found the siren in the engine bay had been disconnected, plugged it back in and nothing, still 'ALARM FAULT' on the dash. Lights don't flash on either lock or unlock.

Marty, should it be klaxson?

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Lights flashing can be switched off in BECM. Switched mine off as I disabled lazy immobiliser etc.

If you don't have the BBUS (Battery Back-Up Sounder) then as far as I'm aware, it should be set to Klaxson, yes. I'm not sure if disconnecting it will have any effect on the BECM detecting an alarm fault or not to be honest. I haven't had the chance to play around with what effects each setting have.

I would take a close look at the pins on the ultrasonic sensor though, as it's a common culprit I imagine after the sensor itself actually failing.

As Grrrr says, you can turn off the alarm arm/disarm light flash - but if you have Alarm Fault showing the dash, I am also not sure that you will get a flash from the lights (even if the option is turned on) as they are for Arm'Disarm indication - if the alarm isn't arming because it thinks there's a fault, then you probably won't get a visual indication.

even with the "alarm fault" coming up when you put the key into the ignition.when you lock the car the indicators flash and the red light in middle of dash still flashes fast for a while then slow down as normal.

Handy to know - so it does set the alarm still - which implies if it does that, then it is related to the ultrasonics - as they are only activated if you are brave enough to superlock it!!

I've had this for about 2 years changed sensor and all door locks but still comes up with alarm fault msg on dash and if I try and superlock it ,it will superlock and then beeps it's horn at me and takes superlock off. Still haven't found the problem.

i have found out from rave that the earth for the ultrasonic sensor is in the left hand side luggage compartment and the other 2 wires come from a 16 way connector righthand side of ecm under drivers seat, gotta wait till i see brother again to be able to test his out.