Security computer and keyless entry

So a couple of months ago, my car suddenly wouldn't start. Took it to my local dealer and they (eventually) found the problem to be the security computer, and replaced it. After I got the car back, I found the OEM keyless entry no longer worked properly. It does lock and unlock the doors as expected. However, when you use the keyless entry to unlock the car, it sets the alarm off. I've taken it back to them a couple of times now, they did TSB 93-007 (door lock sensosr), replaced the security computer a second time on the theory that the new one had an issue, but still no dice.

Any NSX electronics experts have any ideas? Is the keyless entry somehow keyed to the security computer? I wouldn't expect that was the case, since it didn't come with the car and was installed later.

what year NSX?

shawn110975 said:

what year NSX?

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91.

The keyless entry ties into the door lock module and directly or indirectly to the security control unit. Does the alarm go off immediately when you remotely unlock the car or does the alarm only go off after opening the door after you have unlocked the car? If the latter, the problem may be that the security control unit is not getting the signal that the doors have been unlocked by the keyless remote and as such is not disarming. You can confirm this if the little red light next to the door lock button is still flashing.

There is a special add in wiring harness that ties the OEM keyless entry into the door lock and security control module. There is a chance that while replacing the security control unit they may have disturbed some of the wiring to the keyless entry. Unfortunately, the wiring harness and the keyless unit changed sometime around '93, so I can't even go out to my car (2000) to confirm how the harness is connected in it. As I recall, the keyless entry is not included in the base service manual. I think you need to find a copy of the supplemental electrical service manual to get the correct wiring for the keyless entry. With the wiring diagram and test procedure you should be able to figure out where the problem is. You just need to find someone who has that supplement. Failing that, you could go out and have a look at the keyless entry unit and trace the wiring harness to see if there are any obvious loose or broken wires.

Old Guy said:

The keyless entry ties into the door lock module and directly or indirectly to the security control unit. Does the alarm go off immediately when you remotely unlock the car or does the alarm only go off after opening the door after you have unlocked the car?

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The alarm goes off immediately when you unlock the car with the remote, so it seems like the security computer is not aware that the keyless unit is unlocking the door. Using the key works fine.

The latch assembly in the door has two switches, the lockknob switch and the key cylinder switch. I always thought that these two switches were both actuated by the lockmotor; however, perhaps not. The lockknob switch is definitely actuated by the lock motor or the key cylinder; however, It looks like the key cylinder switch is only actuated by the door key. From the wiring diagram, it looks like the sole purpose of the key cylinder switch is to tell the security unit that the door has been locked or unlocked using a key (as opposed to being broken into by forcing the glass open and pulling the lock knob up). The key cylinder switch effectively arms and disarms the security unit.

Since you can lock and unlock the doors, the switches in the latch assembly appear to be working just fine. When you use the keyless entry to unlock the car, the key cylinder switch is not being operated. As a result, the keyless entry unit needs to give an equivalent ‘unlocked’ signal to the security control unit. I am guessing that it does this by applying a ground on the green / yellow wire(s) between the door lock unit and the security unit. If that ground connection has been lost, then the security control unit may not be getting the unlocked message.

Does the lock function of the keyless entry still work OK - doors lock and security system arms without going into alarm? If so, then I really think that you have a broken connection in the wiring (look for the green / yellow wire) between the keyless unit and the door lock control unit. It is also possible that the output of the keyless entry unit has gone dead; however, having that happen coincidently with the other problem seems unlikely.

When I retrofitted the keyless entry to my 2000, my recollection is that the add-in wiring harness was plug-and-play, no wire splicing or tapping required. If your early keyless system required some splicing or taps for it to be wired in, then those are likely spots for a lost connection.

Of course, all of the preceding is informed speculation since we do not have the schematic for the add-in wiring harness for the keyless entry unit!

In fact, the 91 keyless did require 2 pins to be inserted into the security computer wiring harness connector. So that increases the potential chances of issues in the connection between the two modules.

Sketch said:

In fact, the 91 keyless did require 2 pins to be inserted into the security computer wiring harness connector. So that increases the potential chances of issues in the connection between the two modules.

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An excellent place to start looking for a bad connection!

Check all the keyless wiring conections behind/under the glovebox. When they put the new security computer in they probably forgot to wire everything back. See this post (post number 2) for the keyless installation, it shows what needs to be connected and where. http://www.nsxprime.com/forum/showt...OEM-keyless-question?highlight=nsxter+keyless

nsxter said:

Check all the keyless wiring conections behind/under the glovebox. When they put the new security computer in they probably forgot to wire everything back. See this post (post number 2) for the keyless installation, it shows what needs to be connected and where. http://www.nsxprime.com/forum/showt...OEM-keyless-question?highlight=nsxter+keyless

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I copied your 93-05 .pdf because I added the keyless unit to my 2000 about 4 years ago and never kept the instructions. I now see why I didn't keep them - no wiring diagram and little technical info; but, good to have anyway. However, what I really found interesting was the bit later on about how to do a 'cheat' of the immobilizer if you have lost your keys. It talks about getting the Brake Code from the VIN status display. Is the VIN status display something that only the dealerships have? If so, I suspect that I would never be able to access this feature as I have a US market car and Canadian dealers cannot access specific VIN information on US cars.

Old Guy said:

I copied your 93-05 .pdf because I added the keyless unit to my 2000 about 4 years ago and never kept the instructions. I now see why I didn't keep them - no wiring diagram and little technical info; but, good to have anyway.

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The instructions show how and where the oem wiring loom is connected into the car wiring. The OP should just check the connections in his car to see if they match, or if a wire is just not connected. I agree a wiring diagram would help more if you were to need to create a loom yourself. I believe there was another prime member (shawn) that actually figured out the loom and made a few.

Old Guy said:

An excellent place to start looking for a bad connection!

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Just an update, they think the keyless entry unit is bad. They say they checked the wiring, but that the keyless unit is not sending the unlock signal to the security computer. Guess it's time to buy a cheap Legend unit off ebay for testing... anyone know how to reprogram the remotes? Search isn't turning up much.

That seems like too much of a coincidence if the keyless entry system was working prior to the security units replacement!

The remotes can not be reprogrammed in the conventional sense. The code is programmed by punching holes into the conductors on a flexible ribbon in the remote. The series of holes and non-holes establishes the code (its the non adjustable version of a dip switch). You can easily add holes to get a match to an existing code. It may also be necessary to remove a hole to match an existing code. Removing a hole by bridging it with something conducting is much more difficult than adding a new hole. There is a thread on NSXPrime that describes the process of adding holes to match a code. Reality is that if you are going to try a Legend keyless entry system, better get the remotes with it. The chances of being able to successfully modify your existing remotes to talk to the Legend system are low.