Repair car remote key - Page 1
Forum section: electronics / repair

author: sandro
author_rank: Newbie
timestamp: March 31, 2025, 08:19:42 am
content: Hello everyone, I'm trying to repair my car key. The problem is it open/close doors only if it's really close to the car ignition switch. I changed the battery, the antenna transponder but it's still not working. I tested che capacitors pointing the tester to negative and positive on each side of the capacitors, those not circled buzz on one side, circled red no buzzing. I also tested pointing the tester on both side of the capacitors to see if there is a short and the only one buzzing is the one circled yellow. Since I'm no expert maybe I'm just wrong all the way.

author: Kwakerman
author_rank: Regular Contributor
timestamp: March 31, 2025, 08:32:48 am
content: If they are decoupling capacitors I would suspect their values to be around 0.1uF. Unlikely they will cause your issue, I think the yellow capacitor on the second picture is probably a reservoir capacitor for the battery to help keep the battery voltage up when transmitting so may be worth looking at that.Keys can often have dry joints on the pcb as they are often dropped, have a look under a good microscope.I assume you have tried your spare keys to confirm it isn't an issue with the car's receiver?

author: darkspr1te
author_rank: Frequent Contributor
timestamp: March 31, 2025, 08:46:04 am
content: you should also check the voltage of the battery under load, I often get a new cr2032 out to find it's flat already, showing 3.3v but moment you put under load it's down to below 2v .darkspr1te

author: sandro
author_rank: Newbie
timestamp: March 31, 2025, 08:51:57 am
content: Thanks for your replay, the spare doesn't have the remote, Just the Key. I'll try the change the Yellow capacitore but i don't have a microscope. The mechanic tested the Key with a tool and told me the Key wasn't transmitting the signal. I'll check also the battery under load

author: coromonadalix
author_rank: Super Contributor
timestamp: March 31, 2025, 09:46:15 am
content: the yellow would be an inductor, do not touch that, and you have the ones who goes the the big pcb trace who act as an antennai think you should calm down, no pun intended, because you're playing in the antenna section, you may affect it's gain or it's balancegeneral checksnormally all signal length is related to the battery power, have you tried others ones, but a better brand no cheap ones, i did had some problems with cheap / low cost onesnormally check if you dont have any corrosion, liquids traces or the small tact switch who got defectivesand you did not invert the battery position, and maybe sometimes the yellow capacitor who is a tantalum may have a problem, you can check if it is shorted out with an ohm meterand yes as other said, check if the cell drain too fast, that would be a sign but it could be the mcu who could have friedor in the last you could have bad solder / cold joints on one of the ic's pads ?? one is the main processor and the other must be the rf head / emitter, maybe some one with flux and hot hair station could help you, but not overheat the parts

author: ondraN
author_rank: Regular Contributor
timestamp: March 31, 2025, 09:49:36 am
content: Quite often, crystals are defective. Especially when they are exposed to shocks, which is quite common here. It is the brown prism in the second picture and it has the number 13.560 on it. It would take an oscilloscope to believe whether it oscillates (13.56MHz). It is frequency source for transmitter.

author: Psi
author_rank: Super Contributor
timestamp: March 31, 2025, 09:56:05 am
content: Yep, broken/dry solder joints are common,XTAL failure, or detune, from being droppedIf the range is bad but the battery voltage is good under load it's probably either a break in the RF section between the chip output to antenna somewhere, or the xtal.If its a break it could be pcb track/solder crack or a component cracked in half. eg cap.I guess it could also be a cracked ceramic cap that is shorting the battery, but if its that you would expect the battery to be dead within a few days with a short large enough to drop the voltage down enough to limit the range.Some PCB corrosion is also a possibility if its in the RF section, they tend to have a hard life getting wet and the like.But I don't see any in your pic.Lastly it could be the battery terminal. They can corrode and have a high resistance which drops voltage when it tries to transmit. Try pushing down on the battery holder while pushing the button and see if the range is normal again.

author: sandro
author_rank: Newbie
timestamp: March 31, 2025, 10:22:10 am
content: I've tried different batteries, last one is a duracell but I'll check the voltage under load. I'll test the components as you described but I don't have an oscilloscope and in my area they don't make this type of reparations. I don't see corrosion but can't tell if there is some bad solder.

author: faraday
author_rank: Regular Contributor
timestamp: March 31, 2025, 10:33:33 am
content: It look like PSA key.Do you have second key? Does it perform the same way?

author: sandro
author_rank: Newbie
timestamp: March 31, 2025, 11:10:29 am
content: Yes it's a Citroen car key, the spare it's Just the Key, no remote

author: faraday
author_rank: Regular Contributor
timestamp: March 31, 2025, 05:45:23 pm
content: Quote from: sandro on March 31, 2025, 11:10:29 amHave you checked if BSI is in transport mode?

author: sandro
author_rank: Newbie
timestamp: March 31, 2025, 08:19:02 pm
content: I'm learning now about a BSI reset, I'll try even if the mechanic told me it was actually the key not working. The battery with no load it's at 3.25 volts and drops to 3.10 / 3.12 under load, the yellow capacitors reads 1.6 M Ohm

author: Kwakerman
author_rank: Regular Contributor
timestamp: March 31, 2025, 10:25:02 pm
content: 1.6 M ohm doesn't prove the capacitor is ok, only that it isn't shorted. Do you have the ability to measure its capacitance? That 1.6 M could just be parallel paths.

author: fzabkar
author_rank: Super Contributor
timestamp: April 01, 2025, 06:21:23 am
content: Similar remote here:https://www.peugeotforums.com/threads/key-problem.357136/The K110B3 IC appears to be an Infineon TDK 5100 transmitter:https://forum.flipper.net/uploads/short-url/5LPDbB3cnsl4UZM8kzXHBBO7ZhI.pdf

author: ME
author_rank: Frequent Contributor
timestamp: April 02, 2025, 10:59:09 am
content: I used to work at a peugeot dealership in france, Wee used to get issues wth 405 models,the dome over the rx modual gets dusty stopping the ir,just realised yours is rf tho not ir?.

author: sandro
author_rank: Newbie
timestamp: April 02, 2025, 05:11:08 pm
content: In the weekend i'll a friend help me with better equipment

author: JustMeHere
author_rank: Frequent Contributor
timestamp: April 02, 2025, 09:53:35 pm
content: Different approach: if it's just the remote to unlock doors, you can get a cheap replacement on Amazon. For my car, the pairing can be done without any special tools. Just turn the car on/off five times click one of the the new remote's button. $25 each. I'd get two.As far as the immobilizer, that is in the physical key itself. It can be moved to the new key.Google around for your car, I'm sure there are videos out there that cover it.

author: faraday
author_rank: Regular Contributor
timestamp: April 03, 2025, 02:10:20 pm
content: Quote from: JustMeHere on April 02, 2025, 09:53:35 pmNot in PSA, transponder is integrated with remote.

author: BBBbbb
author_rank: Unknown
timestamp: April 03, 2025, 03:12:32 pm
content: Your immobilizer is working and the MCU in that mode gets the power from the LF field and does the comm over it.You seem to have excluded the battery/power issue. Would be beneficial that you do see that voltage on the MCU pin.As others said - either xtal (needed for RF Tx) or antenna (PCB one)If it's xtal - just be careful how you solder new one, they are sensitive to soldering.Antenna (PCB) looks clean, so if the caps you have marked are OK, then go back to XTAL. I would first exclude these before trying to replace the XTAL.

author: u666sa
author_rank: Frequent Contributor
timestamp: April 03, 2025, 04:36:26 pm
content: Two things. Coil must have continuity. Duh.That capacitor is a suspect enough to be replaced on first sight, just in case.

author: BBBbbb
author_rank: Unknown
timestamp: April 04, 2025, 01:52:13 pm
content: That coil is used for the magnetic coupling for the LF part (immobilizer communication) and that is working. No need to thinker around that one.If removing the caps near the xtal, just be careful and quick, xtal is not too tolerant.

author: sandro
author_rank: Newbie
timestamp: April 07, 2025, 09:21:26 am
content: A little update, I removed the Yellow capacitor from the PCB, It reads 0 ohm. Can't measure capacitance at the moment

author: Psi
author_rank: Super Contributor
timestamp: April 07, 2025, 12:14:15 pm
content: if it reads 0 ohms and does not change then the cap is shorted, not all that uncommon for tantalum caps like thatAssuming it's a cap and not an inductor that just looks like a cap. But i'm 99% sure that is a cap, mainly due to the polarity mark.

author: sandro
author_rank: Newbie
timestamp: April 07, 2025, 02:46:33 pm
content: I'm looking for a new one online but not sure about the right value

author: thephil
author_rank: Regular Contributor
timestamp: April 07, 2025, 08:42:38 pm
content: Quote from: sandro on April 07, 2025, 02:46:33 pmThe markings seem to read "C105 V157". So I think it's 10∙10⁵ pF = 1000000pF = 1µF and a 15V rating.Seehttps://forum.digikey.com/t/possible-tantalum-smd-capacitor/3919

author: eurgenca
author_rank: Regular Contributor
timestamp: April 08, 2025, 05:37:26 am
content: Soo. This cap is between + and - pole of battery. If this is shorted how you measure voltage on battery with/without load?

author: tiopepe123
author_rank: Newbie
timestamp: April 08, 2025, 07:29:40 am
content: I've repaired many keys of this model (the cursed model), and they have a problem with the pad joints cracking.These are the small holes that go through the plate.The correct way to repair them is with a wire without a sheath. It's passed through the small hole and soldered. With hot solder, it's extracted so that the solder flows through the hole.Without the wire, the solder doesn't enter and remains superficial.If the car doesn't start, you may have a broken coil, but that's not normal; it's usually the buttons, due to broken pads.The coil should measure a few ohms, not kilohms.I don't speak English, sorry.