Non-Functioning IR Central Locking Feature
 

The IR function for central locking in my ’96 SL600 has stopped working. My central locking feature works perfectly if the mechanical key is used in any of the locks. Thus, only the IR function is inoperable.

However, whenever I use the mechanical key to lock/unlock the car, the red/green lights on the rear view mirror are *not* blinking. I cannot remember if they blink whenever a mechanical key is used, or whether they are for IR operations only.

Question #1 – Can someone test with a similar vintage SL- or S-class, using a mechanical key, to see if the red/green indicators on the rear view mirror blink when using a mechanical key?

Question #2 – Assuming the non-blinking red/green lights (when using a mechanical key) imply the IR function is not working, what components make up the circuit? (Circuit board within the mirror is one, but what does it feed, etc.?)

Any and all input is welcomed! Thanks in advance.

Cheers,
Jeff

I've posted the same exact question here and stumped the techs, as they fumbled about in the dark.

Same thing, my remote can arm/disarm the alarm, and I see the green/red leds flash on the mirror, but the doors do not open/close anymore. For a while they were sporadic, but now they dont work. It works perfectly if I use the key in the lock, or if I use the lock button inside the car.

My indie is ordering a locking computer next week, and after installing it I will bring it to the dealer to reprogram to my key. He's pretty sure its my locking computer that is faulty, so I'll post up if it works.

Mine's a 96 also.

The 1996 is the only year that has the mirror mounted LED's.

Thanks spinedoc for the information. However, our symptoms are different. Your IR Remote causes the red/green lights to flash, indicating the vehicle has received the IR signal - it may not be processing the signal, but your car is receiving it. In my case, the red/green lights do not flash, implying my car is not receiving a signal.

My problem *could* be a bad remote transmitter. But I would like to troubleshoot the problem a bit before making the investment in another key remote.

Oh joy…

Thanks guys for the thoughts.
Cheers,
Jeff

Jeff have you replaced the battery in your remote?

BTW to answer your question, no the leds do not blink when using a key in the doorlock.

Thanks spinedoc! Yes, I have changed the batteries... with the same result.

If your red/green lights do not blink when using the mechanical key, then I am back to not knowing whether my remote has simply failed or if there is an electrical fault in the IR Sensing circuitry. However, in testing my '94 SL500, the red/green lights (mounted in the door handle) do blink when using the mechanical key. Now it is possible the two systems do not use the *exact* same logic, but the red/green lights sequence should probably be the same throughout the R129 model.

My Owner's Manual is quite vague on the whole subject. Nevertheless, I’m going to try resynchronizing the remote to the car.

Anyone else have any ideas, suggestions or comments?

Cheers,
Jeff

Take my answer with a grain of salt, as my remote locking system is fubared at the moment. I cannot remember if the leds flashed when using the key in the door locks when the system used to work. I rarely ever used the key in the lock.

Keep me posted as I'm hoping your problem might be related to mine.

I'm really hoping someone can help by describing where the IR signal goes after leaving the rear view mirror (or door handle for pre-96 models). I have a '94 SL500 that I can swap parts around (assuming their interchangable). But at the moment, have no idea where the circuit leads.
Cheers,
Jeff

I believe the signal goes to the central locking module which is located in the trunk above the battery. From there it sends a signal to the vacuum pump to open/close the doors. I'm no mechanic and only gleaned this educated guess from reading many many posts on the remote locking system.

What really confuses me is that doing a search there must be dozens of SL owners with problems with their remote locking system, but none of the tech/smart guys on here have any suggestions. Even my indie is baffled, my next step is the dealer.

BTW have you tried to resync the remote? Point remote at mirror, press briefly twice, then within 30 seconds put the key in ignition and turn to position 2. Seems to have worked for some. Also make sure as I mentioned, you have a fresh battery in the remote.

Do you own a digital camera with an LCD view screen for framing up the picture? The image sensors in digital cameras are usually sensitive to the IR wavelenght transmitted by the remotes. Set the camera up to take a picture, then aim the remote at the camera and activate it. If you see a bright spot from the remote, it's probably OK. This test doesn't always work...It depends on the camera. And if it does light, it doesn't mean it's transmitting the proper code. But chances are that if both remotes light, at least one has proper code. In my experience, the IR sensor diode in the receiver module is a likely suspect for failure. That's what usually fails in TV set remote receivers. It wouldn't be too difficult for an electronic tech to diagnose / check the receiver for a bad sensor diode, but I realize you don't have that option, especially since the receiver is part of the mirror assembly.

Jeff, if I'm not mistaking your car car is OBD II and you can get a diagnostic reading at your local stealership (free at mine in SoCal).

My indie says I have no OBDII error codes related to the remote locking system.

tecqboy any idea if it's possible for the remote to trigger the red/green leds, but NOT trigger the door locks/alarm? That's what mine is doing.

Good discussion going here – thanks spinedoc, tecqboy and lynns for the input.

I tried resyncing the remote with the vehicle the other day; no effect, no change in symptoms.

Regarding OBDII codes... purely coincidental to this problem, I had to pull the codes yesterday while troubleshooting a severe cylinder-7-8-9 misfire problem. (Still a mystery to me as the problem went away by itself. But that may be a new thread!) The misfire problem caused applicable codes for the affected cylinders, but there were no other codes, Center Locking or otherwise.

Today, I tried the suggestion by tecqboy using a pair of Olympus cameras. Neither captured any indication from the remote. However, I did notice that the little LED inside, behind the red lens, of the remote did *not* blink. This is a very recent development as the LED was blinking earlier in the week. If memory serves, the LED blinks to indicate remote operation and occurs if you hold down the remote button for 2-3 seconds. It’s a fair indicator of battery life, etc. (The batteries n the remote were changed a couple days ago, as a test, so I know they are OK.) I know it is not supposed to be a continuous blink.

With today’s development of non-blinking remote LED, I would normally think the remote is bad. However, the red/green indicators on the mirror do not blink when the mechanical key is used. I want to say this indicates the vehicle is at fault, but cannot say with absolute certainly. Hence, I am hoping someone with a ’96 can confirm that the red/green lights blink when using the mechanical key. This, I think, is the best, definitive test to determine whether the remote or the vehicle is at fault.

Finally, to really complicate matters, some of you may recall that I recently performed surgery on my rear view mirror to solve the infamous R129 Mirror Shake problem (http://www.peachparts.com/shopforum/mercedes-benz-sl-discussion-forum/198658-repairing-r129-rear-view-mirror-shakes-jiggles.html), but that work was completed over two weeks ago and I know absolutely the IR Central Locking System worked after the mirror repair as I used it multiple times after the mirror repair.

Regardless, I will disassemble the mirror today, just to satisfy myself that the connector/cable inside is properly seated and will make sure the red/green lights are properly connected. I’ll also poke around at the controller above the battery (spinedoc’s input as to controller location), though I have not been in that area for many months. Who knows?

Thanks again, and please keep the ideas coming. The more we pool our ideas today, the more knowledge that will be documented to help folks tomorrow.

Cheers,
Jeff

I have a question that I hope isn't too far afield from this: On my newly acquired '96 SL500, what beyond the doors and trunk does, or should, the central locking system lock? I tried locking the car with the remote while sitting in it, the door locks went down, but none of the interior compartments were locked.

Thanks,
Alan