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Hi All

Two days ago my keyless entry stopped working near home. Opened the car using mechanical key and the alarm went off. Started the car by keeping the key near the "Start/Stop" button and was able to start the car and doing this act stopped the alarm. The car kept giving the message that "key was not detected". Moved a 100 yards and the "key not found message went away". Came back and parked next to my flat and the keyless wont work again. So definately some interferance problem. If you lock the car using mechanical key the alarm doesnt go off.

Next day it wouldnt work at 9 but started working at 11am. So thought that problem was gone away.

Today the problem started again. So thought to look a bit deeper into the probelm of this interferance.

Took the Key into work and tested it on the spectrum analyser. When the button is pressed the frequency that the fob transmits at is 434Mhz (433.92 from the crystal in the fob)

However, this frequency is only used for stuff like garage door openers, wireless door bells and even some baby monitors etc. So cant think what will be interfering with this continously.

Next step was to open the keyfob it self. The keyfob has Texas Instruments TMS37126 Remote Access Identification Device IC.

http://www.ti.com/rfid/shtml/prod-trans-Raid.shtml

http://www.ti.com/rfid/docs/manuals/pdfSpecs/RI-TMS37126_ds.pdf

It doesnt say much about the IC but it is a multi transponder so it works as active RFID (low range) at 120-140Khz and also has a microcontroller that works the UHF (i.e. 434 MHZ) longrange.

The microcontroller that controls this keyfob (i.e, the LED, the RFIC and the buttons is an old ROHM BU9870FV microcontroller running at 4mhz, but there is no datasheet for it on the net as far as I can search)

On the back is black square (that I think holds the coil antenna for RFID), and a white ceramic (that I think is the 434mhz antenna) and a Battery holder that holds a coin cell providing 3V (and fob should stop working when the Battery reaches 1.8 - 2.0V)

This is the anatomy of the keyfob for now. I am determined to understand how this interferance is causing a problem, and once I get hold of a directional antenna, I am going to use the spectrum analyser to find interfearing signal and find the culprit device causing it, be it neighbours baby monitor). Wifi routers work in 2.4 ghz and IMHO are too far off in frequency to cause problems.

Some good reads here

http://ignoranceisfutile.wordpress.com/2008/08/04/hack-analysis-of-the-texas-instruments-dst-rfid/

http://www.ti.com/rfid/docs/news/news_releases/2000/rel12-00.shtml

There are some clues to why the device may not work as RFID, (small range) because the car basestation request sends 40 bits number and the keyfob then has to send a 28bit reply to it. This both side transfer is susseptable to magnetic interferance from high voltage cables etc near home. However I still dont understand how the 434Hmz long range UHF transmitter fails to open the car as this is only one way tranmitter.

Hope some one some day will find this info useful. And if the forum allows , I'll keep updating this post with more info about the Lexus IS keyfob as time goes on

Cheers

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Have you tried changing the remote key battery? :winky:

:whistling: it works every where except near my home between 4pm and 11am so i guess its not the Battery, plus both keys fail at the same time and place. did a search in here and seems many ppl had this problem as well

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Have you tried changing the remote key battery? :winky:

:whistling: it works every where except near my home between 4pm and 11am so i guess its not the Battery, plus both keys fail at the same time and place. did a search in here and seems many ppl had this problem as well

First try another Lexus & keyfob in that location - yours might be near the edge in performance. I don't think you will resolve this unless you can bring a spectrum analyser + dipole for directionality home, preferrably a Battery one. Nothing much is licensed to use this part of the spectrum on a continuous signal basis except some older Radio Mikes, so it may well be a sub-harmonic developed in a Wireless Hub, baby alarm or other 2.4 Ghz device, particularly if it uses a 5th Harmonic crystal or multipliers. The interference hours don't suggest anything specific except cheap room-to-room TV senders (these wirelessly spread VCR/DVD output throughout a house). These are truly awful and radiate significant power across the whole spectrum - as do cheap RF O/P Surveillance cameras, some Pub fruit-machines, unscreened till networks and faulty 2m amateur repeaters. The list goes on. If you can attach speaker/phones to the AF O/P of the spectrum analyser; using it in the tuned (non-sweeping) mode you may be able to identify the type of source. Failing all that, OFCOM is empowered to investigate and stop interference. The best of luck to you.

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Have you tried changing the remote key battery? :winky:

:whistling: it works every where except near my home between 4pm and 11am so i guess its not the Battery, plus both keys fail at the same time and place. did a search in here and seems many ppl had this problem as well

First try another Lexus & keyfob in that location - yours might be near the edge in performance. I don't think you will resolve this unless you can bring a spectrum analyser + dipole for directionality home, preferrably a Battery one. Nothing much is licensed to use this part of the spectrum on a continuous signal basis except some older Radio Mikes, so it may well be a sub-harmonic developed in a Wireless Hub, baby alarm or other 2.4 Ghz device, particularly if it uses a 5th Harmonic crystal or multipliers. The interference hours don't suggest anything specific except cheap room-to-room TV senders (these wirelessly spread VCR/DVD output throughout a house). These are truly awful and radiate significant power across the whole spectrum - as do cheap RF O/P Surveillance cameras, some Pub fruit-machines, unscreened till networks and faulty 2m amateur repeaters. The list goes on. If you can attach speaker/phones to the AF O/P of the spectrum analyser; using it in the tuned (non-sweeping) mode you may be able to identify the type of source. Failing all that, OFCOM is empowered to investigate and stop interference. The best of luck to you.

Finding another Lexus and keyfob where I live will be a big problem :) Seems there are only 3 or 4 in town altogether. Thanks for your suggestions, I had not considered harmonics at all, I'll see what I can do with the Battery operated spectrum analyser and if it is possible to find the source.

Thanks for pointing to OFCOM

I found the following link

http://consumers.ofcom.org.uk/tell-us/tv-and-radio/tv-or-radio-interference-or-reception-problems/

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First try another Lexus & keyfob in that location - yours might be near the edge in performance. I don't think you will resolve this unless you can bring a spectrum analyser + dipole for directionality home, preferrably a Battery one. Nothing much is licensed to use this part of the spectrum on a continuous signal basis except some older Radio Mikes, so it may well be a sub-harmonic developed in a Wireless Hub, baby alarm or other 2.4 Ghz device, particularly if it uses a 5th Harmonic crystal or multipliers. The interference hours don't suggest anything specific except cheap room-to-room TV senders (these wirelessly spread VCR/DVD output throughout a house). These are truly awful and radiate significant power across the whole spectrum - as do cheap RF O/P Surveillance cameras, some Pub fruit-machines, unscreened till networks and faulty 2m amateur repeaters. The list goes on. If you can attach speaker/phones to the AF O/P of the spectrum analyser; using it in the tuned (non-sweeping) mode you may be able to identify the type of source. Failing all that, OFCOM is empowered to investigate and stop interference. The best of luck to you.

Finding another Lexus and keyfob where I live will be a big problem :) Seems there are only 3 or 4 in town altogether. Thanks for your suggestions, I had not considered harmonics at all, I'll see what I can do with the Battery operated spectrum analyser and if it is possible to find the source. Thanks for pointing to OFCOM. I found the following link

http://consumers.ofcom.org.uk/tell-us/tv-and-radio/tv-or-radio-interference-or-reception-problems/

First ask the seller for the other fob. The cars come with 2. Secondly, maybe the friendly local Lexus Dealer will help by just driving one to your house before 11am to try it??

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Totally agree with fjcfarrar on this one - I think it's going to be some dirty transmitter spewing out harmonics. I can't see it being a fundamental.

Also, can't see it being a radio amateur as they are (usually) pretty hot on pumping out clean RF.

It's more likely a cheap and nasty piece of gear as fjcfarrar suggests pumping out across the spectrum.

I wish you luck on finding the source - failing that.... Move House !! :winky:

The Ed

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First try another Lexus & keyfob in that location - yours might be near the edge in performance. I don't think you will resolve this unless you can bring a spectrum analyser + dipole for directionality home, preferrably a Battery one. Nothing much is licensed to use this part of the spectrum on a continuous signal basis except some older Radio Mikes, so it may well be a sub-harmonic developed in a Wireless Hub, baby alarm or other 2.4 Ghz device, particularly if it uses a 5th Harmonic crystal or multipliers. The interference hours don't suggest anything specific except cheap room-to-room TV senders (these wirelessly spread VCR/DVD output throughout a house). These are truly awful and radiate significant power across the whole spectrum - as do cheap RF O/P Surveillance cameras, some Pub fruit-machines, unscreened till networks and faulty 2m amateur repeaters. The list goes on. If you can attach speaker/phones to the AF O/P of the spectrum analyser; using it in the tuned (non-sweeping) mode you may be able to identify the type of source. Failing all that, OFCOM is empowered to investigate and stop interference. The best of luck to you.

Finding another Lexus and keyfob where I live will be a big problem :) Seems there are only 3 or 4 in town altogether. Thanks for your suggestions, I had not considered harmonics at all, I'll see what I can do with the Battery operated spectrum analyser and if it is possible to find the source. Thanks for pointing to OFCOM. I found the following link

http://consumers.ofcom.org.uk/tell-us/tv-and-radio/tv-or-radio-interference-or-reception-problems/

First ask the seller for the other fob. The cars come with 2. Secondly, maybe the friendly local Lexus Dealer will help by just driving one to your house before 11am to try it??

Sorry if i didnt mention this well but I have another keyfob and that doesnt work as well.

Nearest lexus dealer is 60 miles away and car was bought second hand out of waranty so dont think they will be too friendly with me :)

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Totally agree with fjcfarrar on this one - I think it's going to be some dirty transmitter spewing out harmonics. I can't see it being a fundamental.

Also, can't see it being a radio amateur as they are (usually) pretty hot on pumping out clean RF.

It's more likely a cheap and nasty piece of gear as fjcfarrar suggests pumping out across the spectrum.

I wish you luck on finding the source - failing that.... Move House !! :winky:

The Ed

OK, brought the spec analyser and found another small signal (-90db) very close (433.8MHZ) and continous, however , the Battery if the spec analyser went down so cant go door to door to see who is responsible.

I agree it must be a cheap electronics that may have gone out of spec or already faulty.

Move House, I was thinking of changing car to IS250 :)

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OK, brought the spec analyser and found another small signal (-90db) very close (433.8MHZ) and continous, however , the battery if the spec analyser went down so cant go door to door to see who is responsible.

I agree it must be a cheap electronics that may have gone out of spec or already faulty.

-90dBm seems a bit too low to be the problem, although the "antenna" coupling into the spectrum analyser may be effectively underestimating the level.

Suspect both car & Fob "receivers" are broadband "TRF" type with poor selectivity, so may respond to large out-of-band signals, so use your Spectrum Analyser to look for anything big from a few MHz upwards. Maybe you could run it in sweep mode indoors from mains power, and look for what changes at about 4 pm & 11 am. Never easy, but if you have a video cam, maybe you could leave it running to record the analyser display at the time the interference starts/stops?

It is worthwhile tracing this problem. Who knows what else it could be affecting?

Lexus owners are nice people, and maybe someone who reads this Forum may be prepared to drop by just to eliminate your car from the equation.

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-90dBm seems a bit too low to be the problem, although the "antenna" coupling into the spectrum analyser may be effectively underestimating the level.

Suspect both car & Fob "receivers" are broadband "TRF" type with poor selectivity, so may respond to large out-of-band signals, so use your Spectrum Analyser to look for anything big from a few MHz upwards. Maybe you could run it in sweep mode indoors from mains power, and look for what changes at about 4 pm & 11 am. Never easy, but if you have a video cam, maybe you could leave it running to record the analyser display at the time the interference starts/stops?

It is worthwhile tracing this problem. Who knows what else it could be affecting?

Lexus owners are nice people, and maybe someone who reads this Forum may be prepared to drop by just to eliminate your car from the equation.

Yes -90dBm is quite low but then the antenna I am using is not tuned to 433mhz. There is a huge signal (-50dBm) standing at 391.6 (possibly SKY earth to Sat) and another at 473mhz (Marine?) the 392 and teh 473 I can see at my work as well so I guess they are not the baddies otherwise the keyfob wouldnt have worked at work as well.

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-90dBm seems a bit too low to be the problem, although the "antenna" coupling into the spectrum analyser may be effectively underestimating the level.

Suspect both car & Fob "receivers" are broadband "TRF" type with poor selectivity, so may respond to large out-of-band signals, so use your Spectrum Analyser to look for anything big from a few MHz upwards. Maybe you could run it in sweep mode indoors from mains power, and look for what changes at about 4 pm & 11 am. Never easy, but if you have a video cam, maybe you could leave it running to record the analyser display at the time the interference starts/stops?

It is worthwhile tracing this problem. Who knows what else it could be affecting?

Lexus owners are nice people, and maybe someone who reads this Forum may be prepared to drop by just to eliminate your car from the equation.

Yes -90dBm is quite low but then the antenna I am using is not tuned to 433mhz. There is a huge signal (-50dBm) standing at 391.6 (possibly SKY earth to Sat) and another at 473mhz (Marine?) the 392 and teh 473 I can see at my work as well so I guess they are not the baddies otherwise the keyfob wouldnt have worked at work as well.

473 MHz is probably ordinary UHF TV - the band is approx 425-900 MHz. Because the "receivers" have simple front-ends, their absolute sensitivity is probably only 10-20dB better at the intended frequency than to any other RF frequency, so the interfering signal can be frequency-decades above or below the operating frequency, and just has to be large enough to swamp the transponding data signals. The big clue is that interference starts about 4 pm. If you slowly sweep (slow sweep is essential not to miss pulsing signals) from a few MHz to 2-3GHz with high resolution bandwidth; it should be possible to spot big (even pulse, or transiently repeated) signals when they start up around 4pm. The problem is the tedious monitoring which is why I suggested recording the screen on a video camera. However, there may be a simpler way. If I remember correctly, many R&S analysers have a composite video output which can be recorded directly on a VCR etc. So, if you can get hold of the analyser over the weekend, and if necessary run an i/p lead and antenna out to where the car is parked, this may give the answer. All this sounds a lot more involved than it is in practice, and shows that without equipment like spectrum analsers - you are completel stuffed!!

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-90dBm seems a bit too low to be the problem, although the "antenna" coupling into the spectrum analyser may be effectively underestimating the level.

Suspect both car & Fob "receivers" are broadband "TRF" type with poor selectivity, so may respond to large out-of-band signals, so use your Spectrum Analyser to look for anything big from a few MHz upwards. Maybe you could run it in sweep mode indoors from mains power, and look for what changes at about 4 pm & 11 am. Never easy, but if you have a video cam, maybe you could leave it running to record the analyser display at the time the interference starts/stops?

It is worthwhile tracing this problem. Who knows what else it could be affecting?

Lexus owners are nice people, and maybe someone who reads this Forum may be prepared to drop by just to eliminate your car from the equation.

Yes -90dBm is quite low but then the antenna I am using is not tuned to 433mhz. There is a huge signal (-50dBm) standing at 391.6 (possibly SKY earth to Sat) and another at 473mhz (Marine?) the 392 and teh 473 I can see at my work as well so I guess they are not the baddies otherwise the keyfob wouldnt have worked at work as well.

473 MHz is probably ordinary UHF TV - the band is approx 425-900 MHz. Because the "receivers" have simple front-ends, their absolute sensitivity is probably only 10-20dB better at the intended frequency than to any other RF frequency, so the interfering signal can be frequency-decades above or below the operating frequency, and just has to be large enough to swamp the transponding data signals. The big clue is that interference starts about 4 pm. If you slowly sweep (slow sweep is essential not to miss pulsing signals) from a few MHz to 2-3GHz with high resolution bandwidth; it should be possible to spot big (even pulse, or transiently repeated) signals when they start up around 4pm. The problem is the tedious monitoring which is why I suggested recording the screen on a video camera. However, there may be a simpler way. If I remember correctly, many R&S analysers have a composite video output which can be recorded directly on a VCR etc. So, if you can get hold of the analyser over the weekend, and if necessary run an i/p lead and antenna out to where the car is parked, this may give the answer. All this sounds a lot more involved than it is in practice, and shows that without equipment like spectrum analsers - you are completel stuffed!!

I can try this but have some problems car has to be parked across the road in designated parkeing space so will have problem getting atnenna there and dont have a or something I can use to record this.

My solutions to this would have been to carry the spec analyser from door to door to see what flat this may have been originating from but the Battery ran down. So I can try doing it again if I can borrow the spec analyser for over the weekend or something.

Found two new things as well

1. Wifes Micra also has keyfob problems, (it only works when held very close to the door) (may be a dying Battery, or overpowering the nissan receiver with signal may work)

2. If I hold the Radio part of the Lexus key next to the Lexus door the LED on the keyfob blinks twice) After that if I open the car with the mechanical key within 30 sec or so the alarm doent sound. So I guess the car knows the key is arround but it wont just open the doors using door buttons or the keyfob buttons for some reason.

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Hi again Shepherd,

Try this then. Knock up an op-amp for high AF gain, driving a crude emitter-follower, ac coupled to headphones. The input terminated with 1k/50R then via a small cap to reject 50Hz etc - all driven by a 9V Battery. Connect a 6" single-turn loop (18 swg tinned copper or coathanger) via a broadband detector to the input. Listen by your car and see if it sounds different when the interference is on, and then triangulate to locate what might be the source. The source direction is effectively looking through the hole the loop forms - but is not wonderfully directional. It could include pointing down to buried cables. You may be able to work out what sort of source it is - ie if it is a burping buzz sound like a mobile phone interfering with a landline, distorted (FM) TV sound and so on. You can spend many happy hours looking like a Wally doing this!!

Big RF signals can have strange effects. There is a section of M4 with what seems to be permanent roadworks, average speed cameras & a forest of aerials. Every time I pass it, my Tracker sends out a false signal that my car has been knicked and simultaneously disables my mobile phone's Bluetooth - which then can only be restored by switching off and rebooting the phone. Not worth investigating because I don't often use the M4, and not a real pain like your problem.

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OK

I get the part from Opamp to headphone. However I dont understand the input to it. can you explain the input bit a bit more. the only opamps i have are some precison amps for instrumentation so dont know if thier gain/bandwidth will be enough but need to check. The only transistors I have are some general purpose ones like BC807 BC817 etc. would they do the job? I am inclined now to build this just for fun if nothing else :)

there is something new to report. the key now works when placed next to the lexus mark on the boot and if then the open or close button is pressed several times.

this is not a fix though.

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OK

I get the part from Opamp to headphone. However I dont understand the input to it. can you explain the input bit a bit more. the only opamps i have are some precison amps for instrumentation so dont know if thier gain/bandwidth will be enough but need to check. The only transistors I have are some general purpose ones like BC807 BC817 etc. would they do the job? I am inclined now to build this just for fun if nothing else :)

there is something new to report. the key now works when placed next to the lexus mark on the boot and if then the open or close button is pressed several times.

this is not a fix though.

Input route: Loop to broadband detector, then termination to suit detector, then small cap say 10nF in series with input of op-amp. Can be any audio op-amp like 741 (a few pence from Maplin or RS) or newer types etc., with feedback set for gain >1000 & using non-inverting input with 10k resistor to Ov mid-point established with 2 off 4K7 resistors. The emitter follower can be any small signal transistor with say 470R to -Vcc in the emitter & collector direct to +Vcc - just to buffer the op-amp but not have a huge standing current ie about 10mA. We are by no means talking hifi here, just lots of audio gain. The most inconvenient bit is that a good broadband detector is needed (borrowed from work?) & most are type N connector, so adapters are required. Some old Marconi detectors are BNC. Also note that most detectors lurking about in lab drawers are buggered. Just any old diode is not going to work. This set-up will receive all fairly large, modulated RF up to a few GHz - but obviously simultaneously. You won't hear steady CW signals but they are unlkely anyway. You could alternatively use a discarded cassette-player/walkman for the AF amp - just disconnect the tape head head and feed in signal from the detector termination there. The object is to seek out whatever starts up when the problem does.

Your subtitle should maybe read "gets more technical daily". Can talk this through more for free on Skype. PM me for username if you wish.

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On 7/30/2010 at 1:11 PM, Shepherd said:

 

Found two new things as well

1. Wifes Micra also has keyfob problems, (it only works when held very close to the door) (may be a dying battery, or overpowering the nissan receiver with signal may work)

2. If I hold the Radio part of the Lexus key next to the Lexus door the Led on the keyfob blinks twice) After that if I open the car with the mechanical key within 30 sec or so the alarm doent sound. So I guess the car knows the key is arround but it wont just open the doors using door buttons or the keyfob buttons for some reason.

I had exactly the same issue Sunday with the is250c.  Couldn't lock it or unlock with fob or keyless entry.

Now the plot thickens..  5 of my neighbours are all having issues.  2 houses with wireless house alarms, 1 caravan with wireless alarm. 1 Toyota RAV4, 1 Mazda, 1 Citroen c1/Aygo and a Nissan quashqui and a Nissan van.. 6 households all within 350m having issues...

Made some enquires to a very local radio ham to see if he was running on 70cm but he wasn't on.  Asked him to keep a log as it looks like ofcom involvement.  Thankfully all the neighbours have said we will club together to keep price cheap.

 

Shepherd.  Any success in solving this ???

 

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I had the same problem ... happened to me when I was working in Langley (nr Heathrow)  ... I called the AA and he was not surprised, apparently he seen this problem a lot in that area ... intermittent interference from the planes, or airport he claimed.  Definately time based issue, as I parked in the same spot a couple of times without problem 

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