Alarm sounds every time car is locked

[KDM]

Hi.

I just bought a C4 Picasso from a dealership. I'd given it a test run and, some seconds after locking it, the alarm sounded. The dealer assured me it was probably just the trade plates interfering with the volumetric sensors.

Unfortunately, I took him at his word and promptly forgot about it. Drove the car home and sure enough, a minute after locking it, it alarmed. Went out, disarmed it, locked it and it went off again.

Back to the dealer. They kept it for nearly 2 weeks (difficulties booking it into a Citroen garage apparently) and it's come back fine. (Well, I say "fine" but how do I test if the alarm is working?)

The dealer said that the Citroen people said that it needed a software upgrade. This is my query: I don't think it's possible for something to have "gone wrong" with the software. The software in these devices tends to be a very fixed entity, unlike mechanical things, which can wear out and fall off. So, is someone at Citroen, or at the dealership talking rubbish, or dumbing something down for me?

Other history: I recall that the dealer had claimed to have changed the battery.

Any thoughts, please? It smells a bit off to me.

[GiveMeABreak]

Hi and welcome.

Software updates to ECUs are indeed applied where required as a result of known issues whilst a car is out in the 'real world' conditions. So that is plausible, however there are several other possibilities to consider:

1) The volumetric sensors are triggered by movement in air volume, so any vents left open where the outside is a bit windy, can result in air being channelled into the vehicle cabin and causing the sensors to trigger the alarm.

One way to test if it is the internal volumetric sensors is to temporarily disable them. Check your manual, but you normally, when turning off the ignition, press and hold the alarm button until the LED remains on, then exit the vehicle and lock it. The alarm engages after about 30 seconds.

If this stops the alarm going off, then you either have air blowing about in the cabin from somewhere like a vent, or an object being blow about in the vehicle causing it to trigger. If none of these things, then you have a faulty volumetric sensor (2) most likely.

2) The other cause is the alarm siren module itself that has an internal battery. This is to provide siren power if the vehicle had its alarm wiring cut in an attempted theft. When the battery has reached end of life it can't be recharged fully, so as it drains below a certain level, it's enough to trigger the alarm. Replacing the siren module usually sorts this out. I've had this happen before.

3) A weak vehicle battery can also be the cause if it is over 5 years old, as the vehicle has a lot of electronic systems and does drain the battery slowly when the vehicle is not being used. If it is over 5 years old, I would recommend a new battery.

[KDM]

Software updates to ECUs are indeed applied where required as a result of known issues whilst a car is out in the 'real world' conditions. So that is plausible,

It sounded right ropey to me: software can't "break". It didn't make sense to me that it should happen to this car, but not all the other cars with this software. Maybe it did and I just didn't hear about it, I suppose.

One way to test if it is the internal volumetric sensors is to temporarily disable them. Check your manual, but you normally, when turning off the ignition, press and hold the alarm button until the LED remains on, then exit the vehicle and lock it. The alarm engages after about 30 seconds.

I had tried that. Not for the reasons given, but just to try and isolate tot hat portion of the alarm. No joy.

2) The other cause is the alarm siren module itself that has an internal battery. This is to provide siren power if the vehicle had its alarm wiring cut in an attempted theft. When the battery has reached end of life it can't be recharged fully, so as it drains below a certain level, it's enough to trigger the alarm. Replacing the siren module usually sorts this out. I've had this happen before.

Noted. Thank you.

A weak vehicle battery can also be the cause if it is over 5 years old,

See, that's annoying me now because the vendor did say they'd replaced the battery, but I can't remember if that was before or after the alarm was demonstrated as faulty.

Meh. It seems fine now. I was just curious....

[GiveMeABreak]

Software doesn't 'break' of course, but can be updated at a later update if there are issues detected with a previous version or the default version installed at factory. The engineers often write a software update to correct the issues. It happens all the time, especially with the BSI and the Engine ECU - sometimes the dealer will do if it is being serviced at a main dealers without advising you if it is required. On other occasions if the car is taken into a main dealer with a specific issue, they may check for a technical service bulletin to find that a software update is required and then they'll action it.

Obviously for those that don't use a main dealer then of course you won't be made aware of this. That's one benefit of going to the dealers and another reason why countless members here have found that there are after sales campaigns (not safety recalls) that are well overdue on their vehicles that they were never aware of as they don't have it main-dealer serviced and third party mechanics or garages ore outside the dealer network so have no access to the bulletins or recalls unless they pay significant sums for access.

Members here have had significant no-cost or reduced cost interventions for issues once we notified them of an outstanding campaign on their vehicle.

[KDM]

Software doesn't 'break' of course, but can be updated at a later update if there are issues detected with a previous version or the default version installed at factory.

Yes, of course. I completely get this. So my question is: how come mine "broke" and not all the other 6 year old C4s with 74k on the clock?

The engineers often write a software update to correct the issues.

Please don't take this the wrong way. You are again 100% correct. What "issues"? The "alarm goes off when you lock the car" bug? Why my car? Why after 74K miles?

It happens all the time, especially with the BSI and the Engine ECU - sometimes the dealer will do if it is being serviced at a main dealers without advising you if it is required. On other occasions if the car is taken into a main dealer with a specific issue, they may check for a technical service bulletin to find that a software update is required and then they'll action it.

Sorry, again, 100% correct: if a software update is required, then a software update is required. My question is still solid: Why is a software update required on my wiper blades or on my foglights, or on my traction control? Did the wiper blades on a specific vehicle, or the foglights on a specific vehicle, etc. fail? Did they craft a specific version of software just for my car? There's nothing special about my car. Why did MY car alarm prompt a software update?

Obviously for those that don't use a main dealer then of course you won't be made aware of this. That's one benefit of going to the dealers and another reason why countless members here have found that there are after sales campaigns (not safety recalls) that are well overdue on their vehicles that they were never aware of as they don't have it main-dealer serviced and third party mechanics or garages ore outside the dealer network so have no access to the bulletins or recalls unless they pay significant sums for access.

Now, THIS is starting to compute. I'm clumsily hobbling towards the same page. I'm thinking previous owner didn't want to pay £75 just to find the problem... repeatedly locked with the blade until they could shift the car onto some other poor sap.

Members here have had significant no-cost or reduced cost interventions for issues once we notified them of an outstanding campaign on their vehicle.

"You" are superstars. I respect that every beggar needs a car and that not every sod can afford to go to a main dealer.
Thanks again.

[GiveMeABreak]

• I was just stating the reasons for software updates. Not every car is driven the same, no do they always have the same exact part numbers as these can be modified in production and some vehicles in a run are supplied with an updated part - this is extremely common. Where this is the case for an ECU it may have a different software version. This is why the same model over the production cycle can have updated parts and software.
• Some cars can go for years without an issue occurring, or the circumstances why an issue occurs may not be the same for all vehicles.
• Another reason is if one ECU is updated, it may require the software for another ECU to be updated. We have seen this lots of times where the BSI has been updated and where this is undertaken, the technician may be directed to ensure the Engine ECU has a software version of at least a certain level as an example top avoid other problems.
• Lastly, because of the reasons I mentioned, not all owners get their cars dealer-serviced so naturally may be missing out on software updates that other owners will have. The dealers do not have addresses of owners after a vehicle has been sold on. They can only advise current owners and get their details for actual 'safety recalls'.
• But back to your alarm issue. I am not aware of any software update fixes for the alarm module. It tends to be a replacement module or sensor that resolves the issue.

[wheeler]

I'll give you an example about the software thing when talking about a car with 75k miles & how come its now needing an update?

Early C3's had a software bug in the BSI where the wipers would freeze & completely stop working until you carried out a reset procedure. What triggered this issue was turning the ignition off on the car just as the wipers came to the rest position. There was a very specific timing of this so this means that 2 different owners with identical cars with identical software and each had the car for 10 years one of them may never ever experience this fault but the other one could have it happen to them 20 times. Anything could have triggered the alarm issue. Leaving the ignition on & letting it drain the battery? anything really.
Also when i update my iphone it usually gives a list this update fixes this issue & that issue. When i read them i dont think i have ever seen one of the issues that it is meant to fix but there are millions & millions of people running the same software as me.

[wheeler]

Out of curiosity when you locked it did the alarm go off at the exact same timing after locking or could it vary?