Peugeot AEC400
Ignition CDI and Immobilizer System


This page shows how to replace the AEC400 CDI+immobilizer of an old Pergeout Speedfight or Trekker with a basic CDI unit. This will only work for (very) old scooters because newer models use the ACI100 immobilizer system which is harder to disable. This information can be misused - but the machines that it applies to are held together by duct-tape and rust-paint, not something that a thief will waste time on. This page is made to help the do-it-your-selfers who are too stubborn to give up when bad electronics get in the way of a working engine.



In 2006 my Peugeot Speedfight 100cc scooter had a problem that almost forced me to dump it. The immobilizer system was causing problems - I had to turn ignition on/off a few times before the engine would be able to start. The link between the key and the immobilizer was unstable and decaying fast, after some time it stopped working completely - the immobilizer indicator would light up constantly: "No way you will be allowed to start this machine."

Getting replacement parts for the immobilizer system was NOT cheap and it had to installed by an authorized Peugeot repair shop. I would end up paying about as much as I had paid for the scooter (I got it second hand for about 6500 dkr). Spending this amount of money was not an option.

I found an internet page about a similar problem with the ACI100 system, based on that and the Haynes "Peugeot Speedfight Service and Repair Manual" I compiled the information that presented here.


Before You Start

After writing this page I have been informed that the AEC400 is very sensitive to low battery. Running out of power or even a weak battery will cause the immobilizer to forget the keys. Try charging/replacing the battery and see if this fix the problem.

With a fully charged battery you can always start the scooter with the red key (unless the immobilizer is completely broken). If the scooter starts with the red key then use the following sequence to "learn" black keys. Make sure you only have one key near the ignition at any time.

a) With red key, turn on ignition but do not start the engine, wait 5 seconds, then remove the key.

b) For each black key, turn on ignition but do not start the engine, wait 5 seconds, then remove the key.

c) Reinsert red key, turn on ignition but do not start the engine, wait 5 seconds, then remove the key.

The immobilizer is now re-encoded and will recognize all of the back keys. If you use the red key again the immobilizer will forget all previously encoded black keys, and you have to repeat the encoding process. If you happen to lose a black key then use the above sequence to "disable" the misplaced key by re-learning the keys that are still in your possession.

Thanks to Bert for providing these useful suggestions.


Identifying an AEC400 system

Peugeot used different immobilizers on their scooters. Take off the body-panels and check the electronic system; an AEC400 system has separate immobilizer and CDI units, while the later ACI100 system has one combined immobilizer+CDI. Also, the label on the CDI box on my Speedfight said AEC400.

The Haynes manual describes the procedure for removing body-panels. The control boxes are located near the battery.


Replacement Parts

You need a CDI for a Speedfight 50 moped without immobilizer. If you have a Speedfight 100 motorcycle (which I do) then make sure that you get one without RPM-limiter. I bought a 'Malossi 558132' CDI from You have to attach wires to the new CDI unit, and because you do not have a plug that fit the new CDI connector you will need some cable-shoes. The CDI connectors will accept standard 220V cable-shoes. You need silicone and shrink tubing or electrical tape to isolate the cable shoes so they do not short-circuit inside the CDI socket.


Background Information

This section provides you with some useless background information that you do not really need to know, you can skip to the "getting down to it" section if you just want to get your hands dirty.

The following figures shows how a CDI hooks into the electrical components of the scooter. Figure 1 shows the basic hookup (that I am making). Since we are replacing the immobilizer, you can add a "secret switch" for manually disabling the engine - Figure 2 shows how to connect such a switch if you want to.

Figure 1

Figure 2

All the wires to/from the AEC400 CDI and immobilizer are black so they are not easy to distinguish. Figure 3 shows the AEC400 CDI seen from the side and what the wires actually are.

Figure 3


Getting down to it

Remove the battery to avoid short circuits. Remove the plastic panels around the battery section of the scooter. On the Speedfight this requires stripping the entire front-end of the scooter. The Haynes manual describes this process nicely - so I will not repeat that here.

The AEC400 CDI has two connectors, eight wires in total - you need four of them. Find some way of marking the four wires before starting to cut anything, tape and a pen will do just fine. Figure 4 below shows the wires that you need. The picture shows the real thing.

Figure 4

Cut the labeled wires and fit cable-shoes. Use shrink tubing (or electrical tape) to isolate the cable shoes to stop them from bending and touching each other when mounted inside the CDI socket. The following pictures show "before and after" for the wires. Cable-shoes have been fitted and then insulated using shrink tube.



Connect the labeled wires to the new CDI unit, hookup is shown in figure 5 and the picture.

Figure 5

Now verify that it works before putting everything back together. Take the spark plug and secure it to the frame somewhere with good connection to avoid damaging the CDI (use a wrench or similar).

Use the kick-starter and check that there is a visible spark - if there is no spark then check that you have turned on the ignition :-) then recheck your connections. If you still cannot see a spark then your problem might not have been the immobilizer to start with; get the Haynes manual and start debugging. If it works: Congratulations you have just gotten rid of your defective immobilizer.

Now that you have seen it work, you need to make sure that it keeps working. Use silicone to fill up the plug of the new CDI unit. The silicone will keep out moist and keep the wires in place when the ride gets rough.

Remove the old AEC400 CDI and immobilizer. When the silicone has hardened place the CDI in the "CDI-holder" next to the battery. Tape up the unused connectors so that they do not accidentally short something. Put back the plastic panels and you are good to go.


Follow Up (2008)

It's been two years since I replaced the CDI and I am very pleased with how the scooter runs. I've had no trouble starting/running the engine at all. Additionally, the Malossi CDI has a slightly more aggressive ignition timing than the AEC400 CDI, this has improved the low and mid-range acceleration a bit.

On the downside, the advanced ignition timing requires high octane fuel, I am now mostly running the engine on octane 98. Without high octane fuel the engine has a tendency to do detonation when it gets hot. To mitigate this, I have changed to a "colder" sparkplug, I am now using a NGK BR9ES which is one step colder than the original NGK BR8ES.

Detonation is a condition where the fuel-mixture in the cylinder chamber is ignited by heat and compression instead of the spark-plug. This ignition happens earlier than it is supposed to and causes an abrupt increase in pressure and engine temperature - in the long run detonation will cause piston and bearings to fail, and it is certainly undesirable.

Then how do you know if detonation occurs in your engine? The pressure spikes beat the engine as if striking it with a hammer - and that is exact sound to listen for. Some people describe the sound as tapping a glass bottle with a screwdriver. Short high-pitch metallic clangs, if you hear that while driving - well that's bad. Detonation depends on your climate, the length of your trips, carburetor setup, and so on. If your scooter is suffering from detonation, try switching to a high-octane fuel, increasing the size of the carburetor main jet, or switching to a colder spark plug.


Follow Up (2010)

Well... it turns out that immobilizers serve a purpose. Some kids stole the scooter, dragged it 500 meters and hit it in an ally. I got It back, but it never really worked well after that - I'm not sure what they did, it does not give a proper spark but I have not looked much into it. I have now acquired a larger Yamaha motorcycle that I use instead. The Peugeot was inexpensive, though maintenance heavy, transportation while it lasted...


Follow Up (2012)

Thanks to Dimitry and Colin for trying out my 2011 request for "alternative" disable of immobilzer - the suggested approach did not work. Also, I have changed "ACE" to "AEC" in the text, for some reason I spelled that wrong from the get-go - figures was not updated.


Follow Up (2018)

Cleaned up wording and language. English is a second language to me and it still shows (though less than before :-)

 < Go Home

Copyright © 2018 - Asger Stenberg