Key Fob Not Working

[Mooly]

The IC is coded to the imobiliser in the car... If you get another similar key I would guess it could be recoded to your car. Depends whether the IC can be "flashed" more than once... perhaps a dealer could advise on that as it's something they will have the software to do.

[morgie]

I originally thought it was a switch but you've got 2 so the chances of both of them faffing up are small. Bridge the switch with a bit of wire and see if the light comes on.

I thought I'd give this a go tonight as I won't have the multimeter until Monday. It didn't work and unfortunately in the process the unlock switch came off the board - d'oh.

[nrgizerbunny]

oh dear,

they are SMD components too! EEK.

[morgie]

oh dear, they are SMD components too! EEK.

I've found someone local with the right experience and tools so hoping to rectify my mistake this week.

put the battery in and check the board has power, 1 end of the multimeter on the ground and the other on a side of the switch, you should have 3v

Checked this today, the board is getting 3v. Repeated this check on the other switch's contact point and it also read 3v. Checked on both sides of the LED, neither gave a reading. Looks like there's an issue somewhere on the board but I don't know where.

I'd like to try and test the LED separately to prove if it's functioning, any idea what power would be safe? E.g. would an AA Battery (~1.6v) blow it?

If the LED is broken in some way should this stop the key fob functioning?

[nrgizerbunny]

you'll need a 240R resistor and probably 3v

LEDs don't work on the voltage so much its the current draw.

[Mooly]

You will probably get the LED to light by just using the DVM on "diode test". Try the meter leads both ways round.

The meter applies a small voltage, enough to light a red LED (Volt drop of different coloured LEDs varies.... red is the lowest at around 1.7 so just within the range of a DVM on diode test).

[morgie]

You will probably get the LED to light by just using the DVM on "diode test". Try the meter leads both ways round.

The meter applies a small voltage, enough to light a red LED (Volt drop of different coloured LEDs varies.... red is the lowest at around 1.7 so just within the range of a DVM on diode test).

Thanks - that did the trick, LED is functional. Getting the switch soldered back on tonight. Still don't know what's not functioning with the board.

[morgie]

Switch is back on. Not sure what to try next - any thoughts?

I called Toyota, they said they could have a look at it, but then if it needs replacing it would be £105.93 plus 30 mins labour so £144.

[Mooly]

It's looking a bit like it's going to beyond repair easily.

I still feel cracked print or something physical is most likely... and it can be very very hard to spot. Can you trace the 3 volts (supply and return) to the IC. Is there 3 volts across that large "yellow" component next to the IC.

True fault finding now needs an oscilloscope to take things further and to check the "clock" on the microprocessor runs when a button is pressed etc which is getting a bit advanced... and the best you could hope for is it helped find a fault as mentioned above.

[nrgizerbunny]

i second what mooly said.

Chances are its a broken track. It was working before and the only thing you did was change the Battery. Chances of IC failure are very very small.

[nrgizerbunny]

heat it in the oven to 50C for about 20 minutes, then try it.

cracks may bridge and then you will isolate the fault.