C3 Phase I random starting issues

[ozvtr]

The only key I have is a simple key which is a copy of the original Citroen key (the two originals were lost or stolen). In the last few months I've been getting the message "anti theft fault" but not always, and the car will not ignite. It seems I cannot turn off the car and restart it immediately, but I have to remove the key and wait, as mentioned in the other thread as well.

Unless the stop/start fails EVERY TIME you get the anti theft fault, I would say you have two faults. One in the key and one in the stop/start.
As I said, if the engine ECU does not get the correct code from the key, the engine will never start!! Or in this case "turn over". So I would suspect the RFID chip in the key. Being a "copy" it could be a bit dodgy.

Something to try: next time the engine fails to "turn over" AND you get the anti theft message, see if the interior light turns on when you remove the key. Trust me on this one.

[frenchc3]

The only key I have is a simple key which is a copy of the original Citroen key (the two originals were lost or stolen). In the last few months I've been getting the message "anti theft fault" but not always, and the car will not ignite. It seems I cannot turn off the car and restart it immediately, but I have to remove the key and wait, as mentioned in the other thread as well.

Unless the stop/start fails EVERY TIME you get the anti theft fault, I would say you have two faults. One in the key and one in the stop/start.
As I said, if the engine ECU does not get the correct code from the key, the engine will never start!! Or in this case "turn over". So I would suspect the RFID chip in the key. Being a "copy" it could be a bit dodgy.

Something to try: next time the engine fails to "turn over" AND you get the anti theft message, see if the interior light turns on when you remove the key. Trust me on this one.

The star/stop fails message comes on every time, it's the anti theft that only comes on occasionally. I just tried what you suggested, the internal light doesn't turn on when I get the anti theft message and I remove the key. It seems also that once I get the anti theft message I have to wait a bit to try again.

Another strange thing I noticed, I was able to start the car once without keeping the brake pedal pressed, that's very strange as usually you get a message if you don't have the car in N and the brake pressed and the car won't even attempt to start. I also noticed that if I can start the car if I do it quickly before the anti-theft message comes on. I wonder if the "energy saving mode" also has anything to do with it. It seems it comes on too quickly.

Is the starter/alternator the culprit? I looked it up and it's very expensive, I don't really have the money for it. Should I start by changing the battery? What can I do?

[PaulC5]

When it does not start if you leave the key in the ignition switch and open the driver's door do you get a warning message ? Most cars do this provided the key is being recognised by the immobiliser.

[ozvtr]

I just tried what you suggested, the internal light doesn't turn on when I get the anti theft message and I remove the key. It seems also that once I get the anti theft message I have to wait a bit to try again.

OK. When you turn the ignition off, the car activates the transponder reader around the ignition barrel. While it gets a "ping" from the transponder in the key, the car knows that the key is still in the lock. When the key is removed, the "pings" stop, and the car knows the key has been removed, and so it turns the interior light on. BUT if it "thinks" that there never was a key in the lock in the first place, it wont turn the interior light on. So the car was NOT getting "pings" from your key, at any point in time! So I postulate that the transponder in the key is dodgy. That's causing your "anti theft" fault and the engine not starting, UNDER THOSE CIRCUMSTANCES!

Another strange thing I noticed, I was able to start the car once without keeping the brake pedal pressed, that's very strange as usually you get a message if you don't have the car in N and the brake pressed and the car won't even attempt to start.

The brake switch has two sets of contacts. One set actually turns the brake lights on and off. The Other "auxiliary" contacts are used to both check the position of the brake light contacts AND signal to other systems that you have put the brakes on. The engine, the auto gearbox and other systems (stop/start in this case) use the data of whether you are using the brakes or not. These contacts are known to cause trouble. Sticking on or sticking off! A classic fault is not being able to get the automatic shifter to come out of PARK because it wont unlock when you put your foot on the brake pedal. So I'm not surprised.

I also noticed that if I can start the car if I do it quickly before the anti-theft message comes on. I wonder if the "energy saving mode" also has anything to do with it. It seems it comes on too quickly.

I think this is to do with the bad transponder chip in the key more than anything.

Is the starter/alternator the culprit? I looked it up and it's very expensive, I don't really have the money for it. Should I start by changing the battery? What can I do?

I'm sorry but I don't know. There isn't enough information.
I would recommend finding someone with a LEXIA or a scan tool that can read the fault codes stored in the stop/start ECU. That should give you a clue as to where the fault lies. Those little OBDII scanners wont do it!
The fault is most likely in the stop/start alternator, the stop/start ECU or the wiring and electrical connections. Replacing things willy-nilly could prove fruitless and expensive.

[ozvtr]

Should I start by changing the battery?

No. I was a bit premature in my first post. That auxiliary battery has nothing to do with your current problem.
If you started loosing the time or the dash flickers when the stop/start restarts the engine, then maybe think about it. But considering that you are turning off the stop/start...I wouldn't worry about it all.

[frenchc3]

I'm sorry but I don't know. There isn't enough information.
I would recommend finding someone with a LEXIA or a scan tool that can read the fault codes stored in the stop/start ECU. That should give you a clue as to where the fault lies. Those little OBDII scanners wont do it!
The fault is most likely in the stop/start alternator, the stop/start ECU or the wiring and electrical connections. Replacing things willy-nilly could prove fruitless and expensive.

Thanks a lot, this is very useful information, and I think we can conclude there are two separate issues here that both relate to starting the car. I will try to get a new key as well and get a complete scan of the codes.

[frenchc3]

Should I start by changing the battery?

No. I was a bit premature in my first post. That auxiliary battery has nothing to do with your current problem.
If you started loosing the time or the dash flickers when the stop/start restarts the engine, then maybe think about it. But considering that you are turning off the stop/start...I wouldn't worry about it all.

I agree on the aux battery, I was thinking more about replacing the main battery. I am pretty sure it's not the problem, but I guess I will have to replace it sooner or later.