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1990LS400

Keyless Entry Works Only Below 32fº

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For the past several years the keyless entry in my 90 LS400 has functioned only in winter. It now functions only when the temperature is below about 32Fº. The colder the weather, the more reliably the keyless entry works. My guess is that the keyless entry stops working as the interior temperature of the car rises although I have never tried leaving the heater off to verify this and it is a long time until winter.

My local repair shop is baffled and does not seem to really want to chase electrical problems. Any ideas?

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I'll answer my own question from from last year since the person that bought my 90 LS last November told me yesterday what fixed the problem.

The ROM card was not seated in the slot in the keyless entry module in the trunk. The current owner told me that he had to press fairly hard to get the card to snap into place. He also said that he could see that the card was not fully inserted by comparing the size of the card with the size of the slot.

Not coincidentally, the ROM card and keys were replaced several times shortly after I bought the car in 1990 when I found that the keyless entry would not work when near several shopping centers. The dealer finally gave up when none of the ROM card / key changes solved the problem.

The keyless entry worked fairly reliably for about 10 years until it started working only in winter in about 2000. My guess is that hitting a large bump or being rear-ended very hard ($10,000 damage) in 2000 shook the ROM card loose. It was probably never properly seated in the first place.

I still guess that cold weather caused the ROM card to contract which somehow caused the terminals to make contact. Very strange because I would have expected the opposite - that it would have worked better in warm weather.

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This is Toby. I bought the car from Jim.

When at the back of the car, the box is located farther back in the trunk behind the power antenna. It is not the box right next to the antenna. It is the next one. In order to get there, the left trunk side cover needs to be removed. To do that remove the screws around the toolkit (open the toolkit), there is four I think and then you can remove the cover piece and toolkit(both will come out as one unit). There is a metal piece of the car frame that separates the antenna assembly from the remote module. There will be two nuts on that metal piece that hold the module onto the frame that need to be removed and then you can bring the box through the frame opening. The ROM piece that comes paired with the key is in the side of the module. This ROM piece is about 1.5" x 1.5".

Be very carefull when handling this ROM Pull it out gently and re-seat it. Be firm but do not break it by pushing to hard. If that doesn't work, there are other diagnostic steps that are in the shop manual that I can email you. Let me know.

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Hey Roy,

I had nothing to do with the diagnosis. The buyer of my 90 LS is a very bright (better say that - he may read this) amateur mechanic (and network security engineer) and is willing to take on some very complex diagnosis and repair tasks.

On the 90 LS, the wireless receiver is on the left side of the trunk behind the trim panel. However, I checked the repair manuals for my 2000 LS just now and it shows most of the components being under the dash, with the "wireless door lock tuner" being in the area behind the front passenger side air vent.

And of course most of the information about the wireless door lock system is in the manual just before the section on the rear power seat (with multiple motors controlling each rear headrest) sold in Taiwan - I have no idea why that made it into the manuals for US/Canadian models.

Just got back from a weekend trip to Iowa City to watch the nephew play for the U of I Hawkeyes. The trip computer showed a tank average of 29.3 mph for the trip home! Never came even close to that in the old 90 LS.

Take care!

Jim

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Good call Jim, I didn't even check the year of his car. I am sure you are correct that it is not in the same place or the same type in his 99. The newer models from 94 on don't have the lock system that is in the 90 to 93 models.

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This is Toby. I bought the car from Jim.

When at the back of the car, the box is located farther back in the trunk behind the power antenna. It is not the box right next to the antenna. It is the next one. In order to get there, the left trunk side cover needs to be removed. To do that remove the screws around the toolkit (open the toolkit), there is four I think and then you can remove the cover piece and toolkit(both will come out as one unit). There is a metal piece of the car frame that separates the antenna assembly from the remote module. There will be two nuts on that metal piece that hold the module onto the frame that need to be removed and then you can bring the box through the frame opening. The ROM piece that comes paired with the key is in the side of the module. This ROM piece is about 1.5" x 1.5".

Be very carefull when handling this ROM Pull it out gently and re-seat it. Be firm but do not break it by pushing to hard. If that doesn't work, there are other diagnostic steps that are in the shop manual that I can email you. Let me know.

Hello!

I have the same LS400 1991 model. Is it possible to send a picture of the location of this remote control module? Also could you send other diagnostic steps as you mentioned in your reply?

my email is: jhussain@yahoo.com

Thanks,

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This is Toby. I bought the car from Jim.

When at the back of the car, the box is located farther back in the trunk behind the power antenna. It is not the box right next to the antenna. It is the next one. In order to get there, the left trunk side cover needs to be removed. To do that remove the screws around the toolkit (open the toolkit), there is four I think and then you can remove the cover piece and toolkit(both will come out as one unit). There is a metal piece of the car frame that separates the antenna assembly from the remote module. There will be two nuts on that metal piece that hold the module onto the frame that need to be removed and then you can bring the box through the frame opening. The ROM piece that comes paired with the key is in the side of the module. This ROM piece is about 1.5" x 1.5".

Be very carefull when handling this ROM Pull it out gently and re-seat it. Be firm but do not break it by pushing to hard. If that doesn't work, there are other diagnostic steps that are in the shop manual that I can email you. Let me know.

Hi,hope all is well with you and yours. i really need your help.i owned a '90 LS400.The key-less entry doesn't work,after replacing then battery.(i took a month to actually replace the battery)I was then told that i need to reprogram the system, in order for it to work. i followed your instructions for the above steps. This "Rom" piece was attached to the module by a single screw.There are two wires runs from the Rom and connects to a harness independently.On the Module they are: Female connection and a gray wired that runs on its own. I can take pics for further clarification.

I am unsure what i need to "pull out and re-set" from this Module. Now, the trunk latch wouldn't unlock with the ignition key after i manually locked it.any other suggestions.

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i owned a '90 LS400.The key-less entry doesn't work,after replacing then battery.(i took a month to actually replace the battery)I was then told that i need to reprogram the system, in order for it to work. i followed your instructions for the above steps. This "Rom" piece was attached to the module by a single screw.There are two wires runs from the Rom and connects to a harness independently.On the Module they are: Female connection and a gray wired that runs on its own. I can take pics for further clarification.

I am unsure what i need to "pull out and re-set" from this Module. Now, the trunk latch wouldn't unlock with the ignition key after i manually locked it.any other suggestions.

When you say "Now, the trunk latch wouldn't unlock with the ignition key", do you mean by pressing the button on the key or by trying to unlock the trunk manually with the ignition key?

I've never heard anything about having to "reprogram the system" in a 90-92 LS400 after replacing a key battery -- the ROM chip and keys for the 90-92 LS400 come as a set and don't require programming. If your trunk won't unlock manually with your key, then either the key or more likely the trunk lock cylinder is worn. I remember the trunk lock cylinder in my 90 getting a little balky by the time I sold it in 2003. Lubing it with lock lube seemed to help -- do not use WD40 (!!!)and I doubt that silicon spray is a good idea either.

Sorry I can't help more. I never looked at the ROM chip in my 90 -- the person who bought my 90 from me in '03 is the one who figured it out and provided the above instructions.

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Hi,

So I am guessing you took off the two bright silver nuts that hold the module to the car. If so, now try to pull it out a little to look at both ends of the metal module. On one end is a white box looking item attached to the metal module. That white box will be labeled "noise filter". Now, at that same end but on either side of the metal module you will see black tape covering the side of the metal module, under that tape is the rom card I pulled out and pushed back in to re-seat. That card is sold with the key and they match frequency. There should not be any programming involved for the 90-93 model years.

One more thing, be sure the dash switch for your remote lock systen wasn't hit by your knee and is in the the off position. Also verify your key battery was installed correctly. They key sensor is in the rear glass so put the key close to it as well when testing to rule out radio interference affecting your key range. If this doesn't work, we need to go through the key test to make sure it is working (let me know) and then go from there.

Toby

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