Early C3 transponder key fob parts (plip) fix

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Model: C3 2002-2005, Original shape model
Year: 2002 (52)
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Fuel Type: Diesel
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The 2 button transponder - '6554RE' (transmitter/responder) keys remote unlock/lock security is controlled by a Motorola 75078020 - 510164 in TQFP32 style package with a surface mount crystal resonator at 13.560MHz in the fob. The unlock/lock security is based on a rolling code that changes with each press of the button on the fob. The theory is that the car and fob are 'married' and the car knows the next code the fob will send, if the code is as expected the car unlocks/locks. There is a margin that the car will accept from the fob in the window of 256 codes in advance. This cures the problem of the fob button being pressed out of range of the car, incrementing the rolling code with the car unaware that the code has stepped forward. If the a fob button is pressed more that 256 times out of range of the car, the car will no longer accept the fobs code when in range. 256 sounds like a lot, but a faulty switch may cause 100s of increments. The solution is to re-synchronise the key to the car - follow these fob re-syncing instructions.

The immobiliser feature of the car utilises a transponder ring around the ignition barrel which communicates with the transponder - an 'ID46' '(Crypto II)' 'HITAG2' (available here) found in the fob. The transponder code in the PCF7936AS is known by the car and only disengages the immobiliser when the transponder codes match. The transponders location is arrowed in the picture of the fob, below.
PCF7836AS in Citroen C3 fob
PCF7836AS in Citroen C3 fob

a closer view of the transponder chip - an 'ID46' 'Crypto II' or 'HITAG2' - PCF7936AS (This one by Philips, later ones by NXP - a company founded by Philips, but they all do the same thing).
PCF7936AS 'ID46' Transponder chip
PCF7936AS 'ID46' Transponder chip

and the transponder ring around the ignition barrel is pictured below. The ring communicates with the 'ID46' PCF7936AS chip in the key to disable the immobiliser.
Transponder ring location around the ignition barrel on a Citroen C3
Transponder ring location around the ignition barrel on a Citroen C3

Common faults with the early C3 key fob include worn out plastic parts on the lock or unlock buttons.
If your switch still works, but the plastic has become detached or worn out, the solution is to replace the plastic parts from one these listings for new parts (click) on eBay - match the picture on ebay to your style of key including the blade shape and the number of buttons.

broken plip transponder repair
broken plip transponder repair
To open the case firstly remove the screw
the case screw
the case screw

Then lever open the clamshell case with a coin
lever open the clamshell with a coin
lever open the clamshell with a coin

Remove the circuit board, key blade and the small transponder part (red arrow below) and transfer these to the new parts fob you purchased from here.
C3 key transponder fob repair arrowed
C3 key transponder fob repair arrowed

If your problem is more serious where pressing one of the buttons doesn't work, for example the car locks remotely, but not unlocks or unlocks remotely but won't lock then the switch on the circuit board may be faulty. The easiest (if you can find someone that can solder) is to replace the faulty switch from one of these listings on ebay for new switches match the style of switch you have with one in the listings. By fitting a new switch or switches you avoid the need for any reprogramming.
The two switches responsible for locking and unlocking the car are arrowed in the picture below.

the fob switches are arrowed
the fob switches are arrowed

These repair switch kits require some soldering skills to remove and fit switches but its not too difficult if you have those skills.

If your fob appears dead, its worth trying a new battery in the fob, a CR2016 battery (here) or a DL1620 battery (here)

The battery fits to the electronic board in the fob plastics, its very tight to remove but does pull out eventually.
The fob battery goes in here
The fob battery goes in here
Later batteries fit to the plastic case and can make a poor contact with the electronics.


If you find the central remote locking doesn't work the next morning and you have fitted a new radio/cd recently - check your wiring on the power plug of the radio/cd install because pins 4 and 7 on the C3 are reversed to the ISO specification.

If your key unlocks/locks the car, but won't start it, then you have a problem with the transponder. Its missing or not configured to the car correctly.

If your key won't lock/unlock remotely but it does start the car, then there is a problem with the synchronisation, flat 2016 battery in the remote, faulty switches or damaged circuit board in the fob.


The later cars have a different style remote locking key which take a Duracell 1620 Battery


Upgrading or converting the key style found above into the flip style where the blade retracts into the body can be done by following the video instructions here convert C3 fob to flip (click).
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My Name: eastonch

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Model: C3 2002-2005, Original shape model
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Thanks, fixed one of my fobs just buy opening it up and positioning everything, think the button had 'slipped' works fine after a battery replacement too.
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Model: C3 2002-2005, Original shape model
Year: 2002 (02)
Engine Size: 1.4 (16v)
Fuel Type: Diesel
Mileage: 140000
Trim Level: Exclusive
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: RHD (UK)
Engine name: DV4 16-valve diesel (90 PS)
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Broken keyfob switches repair, much cheaper than a new fob and programming by the dealer ;)

The rubber buttons had fallen off a while ago exposing the switches which ultimately led to their demise leading to a useless remote locking fob.
buttons missing from C3 fob fix
buttons missing from C3 fob fix
How to:
Disassemble, remove the battery, unsolder the broken switches, solder in the new switches, refit the battery, re-assemble with a new case, test.

Parts:
A pair of switches from eBay
A new plastic case from ebay
If you have a different style fob, the parts are also available, just match your with the pictures in the parts listings

Broken
Broken switches on a Citroen C3 key fob
Broken switches on a Citroen C3 key fob
Remove the damaged switches by unsoldering
Remove the damaged switch by unsoldering
Remove the damaged switch by unsoldering
Both switches removed
Both switches removed
Both switches removed
New switches
new switches to be fitted
new switches to be fitted
Fit new switches in place of the old broken ones
fit new switches in place of the broken ones
fit new switches in place of the broken ones
2 new switches fitted
2 new switches fitted
2 new switches fitted
Refit the battery, reassemble the board into the new case, not forgetting the hidden immo chip. Test remote central locking and engine starting :)
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