Automotive Lock/Unlock Key - Strange behavior when testing with meter. - Page 1
Forum section: electronics / repair

author: LiftedTrace
author_rank: Regular Contributor
timestamp: June 03, 2024, 02:52:10 am
content: I have this key for my car with buttons to lock and unlock remotely ( Like all cars I guess now a days).Recently it began acting strange and requiring me to press the lock/unlock buttons multiple times before it finally worked.I was thinking possible battery being low or maybe faulty switch, so I pulled the key apart to test.What I found was strange and this is reason for my post.Measuring the switch on volts and watching to see if it was working, meter placed across the switch...when I pressed the button, the key worked perfect. Take the leads off and it doesn't work any more.The battery measured 3.05V and its CR2016 3V cell. New they measure 3.3 so I guess it was a bit low, but my wife's key works flawlessly and I checked her battery and it also measured 3.05.Replacing the battery does fix the issue, but only for a month or so, then its back to not working.But what I cannot understand is why the key works perfect when the meter leads are across the switch and doesn't work when disconnected.

author: mikerj
author_rank: Super Contributor
timestamp: June 03, 2024, 05:01:44 am
content: Possibly cracked solder joints on the switch, applying pressure with meter probes closes the circuit and makes it work correctly.

author: LiftedTrace
author_rank: Regular Contributor
timestamp: June 05, 2024, 01:26:52 am
content: Quote from: mikerj on June 03, 2024, 05:01:44 amYeah Its not bad joints. It does it when checking across any switch.I was thinking maybe the meter leads was changing the transmit freq or something? Maybe its drifting from age and the meter got it closer? I really have no clue how the keys transmit so I am just pulling out of my butt.Is that even a possibility?

author: amyk
author_rank: Super Contributor
timestamp: June 05, 2024, 04:16:23 am
content: It is possible the meter leads acted as a larger antenna. If the same thing happens with the leads unplugged from the meter, that would be the likely cause.

author: perieanuo
author_rank: Frequent Contributor
timestamp: June 05, 2024, 04:34:44 pm
content: sometimes in our lab we stare 5 minutes on proffessional microscopes to see a cracked rezistor or some layout shorts or interruptions. try harder, those are just switches, i don't believe the antenna proposal. it's probably some broken track or broken resisor series with the switch or bad soldering.

author: jzx
author_rank: Regular Contributor
timestamp: June 05, 2024, 06:28:03 pm
content: Try to push on the same point but with an isolating stick to see if the works or not. Can be a cracked solder on another point and when you apply force the board is flexing.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: June 06, 2024, 08:17:17 am
content: The switches have probably got worn/dirty resulting in a voltage drop through the switch, have seen similar issues myself on a toyota remote, replacing the switches fixed it in my case.

author: LiftedTrace
author_rank: Regular Contributor
timestamp: June 09, 2024, 05:34:59 am
content: Thanks all for all the input.Problem I have with broken solder joints is when I put a fresh battery in, it works without fail. Put the original one in, and it works great with test leads, but by itself, it is very poor.