850 station wagon door remote control won´t o perate doors - lights flash normally

I had a 1996 Volvo 850 some years ago to which I fitted an "after market" remote receiver which interfaced to the Volvo central locking system. To do this I needed to find out some things about how the Volvo receiver worked, which I did by trial and error measurements.

The connector for the receiver, behind the glove box is designated 4/19 and has 5 pins: pin 1 - wire black (ground) pin 2 - not used pin 3 - wire yellow/green (receiver output) pin 4 - wire yellow/violet (+12V accessory) pin 5 - wire red (permanent +12V)

The receiver puts out a 100ms (milli-second) positive going pulse on pin 3 to lock the doors and a 200ms pulse to unlock. There was a tolerance of something like +/- 50ms - I forget the exact figure and it is probably different for lock and unlock.

You stated that when the failure began the doors would lock (short pulse) but not unlock (long pulse) - you seem to have made a mistake in your typing and that's how I interpreted what you wrote. But it doesn't matter anyway. It looks like either 1) the pulse former in your receiver is "out of spec" and no longer sending the correct length pulse to the car's central locking system or 2) the car's central locking system is no longer accepting the "standard" pulse lengths for lock/unlock.

Unless you have a friend who can trouble shoot the electronics for you, I'd suggest you get hold of another receiver, buy or borrow one and substitute if for yours. If it doesn't fix the problem, the trouble is most likely the central locking module.

Regards Barry

Hi Barry, thanks for your detailed answer. yes I mistyped. It would lock but not unlock.

I am not firm in electronics at all and don´t have an oscillocope to measure the signals. I think my receiver is mounted on the cover above my legs down from the steering wheel. Maybe the previous owner has already changed the receiver because of malfunction? I might contact him, I still have his e-mail.

Is there an electric switch (1) operated by the receiver which in turn operates another electric switch (2) in the central locking module? Could it be that the hypothetical switch (1) is malfunctioning and could be changed or is it all in the electronics of the receiver?

Could the central locking module be malfunctioning, if it works ok when operated by keys in a lock?

Regards Franz47

Have you replaced the battery in the remote control?

I Just looked at that device. It is NOT the locking system receiver, it is the Eberspächer engine heater remote control receiver.

I just checked the voltage of the two 3 V batteries. The pack reads 5,96 V. I switched the batteries from the unit of the second remote control in our family which is rarely ever used - the doors open but won´t close, the voltage of the battery pack there is 5,98 V. So that should not be a battery problem. I would also expect that the car either reacts or not at all. Now when trying to close the lights on the car flash - the signal is received. But no mechanical action.

if one is very paranoic one could think that the two battery packs were bought at the same time (which they weren´t) and voltage without current is ok but under use the voltage falls too low to give a good signal. But again I would expect a binarian behaviour - either works or not at all?

Today I consulted my VADIS and delved into the spaces under the dashboard on both sides and behind the glove box. Vadis shows a control unit 9128928 which should be on the right side - I could not locate anything which reminded me of that part. When googling with that part number I found e.g.

On the left side in the passenger compartment there should be a relay Volvo number 9128903. I could locate a relay in the relay group, but mine had Volvo number 9177999. Googling that results e.g. in

Could a low battery in the keys really cause the problem?

Electronic things are complex, work differently, and are designed differently. It is possible that an electronic key needs to do more "work" to send an unlock signal than a lock signal. So with a borderline battery, some signals might work and other might not.

Or it could be that an unlock signal is designed to intentionally be "weaker" requiring you to be closer to the car. Whereas a lock signal would work from a very far distance. That would be a good security feature/design.

And then other signals from other wireless devices can block the signals of remotes. It could be that with a strong remote battery, the signals get through the "chatter" in the air. But with a weak remote battery, they barely get through or go through distorted. Sort of like you are not talking loud enough with a weak voice - the listener can't quite make out what you are saying. Maybe "some" words can be understood.

But most important of all, the battery is easy to replace in a remote (get a replacement at a hardware store). As opposed to troubleshooting the electronics in the car. So it is a good idea to replace the batteries - just to eliminate the possibility of that being the problem.

Note batteries can fail in a manner that they have voltage, but little power when trying to use them.

Then next if replacing the remote battery does not resolve the problem, try driving to a different location - maybe to a rural area where there would not be any other wireless devices around. See if the remote works there.

If still not working, THEN dive into the vehicle electronics.

Here no one's remotes worked due to other "signals in the air"...

The receiver in a right hand drive 850 is accessed by removing the glove box, and it's mounted in the space to the left of the glove box hole. From the wiring diagrams I have, on the left hand drive 850 it's the mirror image. That is it's still accessed by removing the glove box and is to the right.

The receiver output would be the first thing to check, but without an oscilloscope to check the presence and length of the locking/unlocking pulses you have a problem. As I suggested, substituting a borrowed receiver would be the next best thing. If that doesn't fix the problem, move to the central locking system. I can't offer any help there as I never needed to investigate it.

BTW looking at my notes (from 2008) the unlock pulse was from 150 to 250ms and the lock pulse 75 to 120ms. I actually measured this with an adjustable pulse generator. This was for my car and it could vary between cars. That's why I chose 100ms for lock and 200ms for unlock when I designed my interface cct.

Barry

A spontaneous healing has taken place!!!

At first thanks for all who gave input here.

Since last week, when I had time to work on the problem, the car was parked most days during the week. Yesterday I drove to work, when parking it - same fault as usual. After work I drove about 80 km, parked it. Then another short drive in the evening and when parking at the restaurants parking lot I pressed the key as usual and suddenly heard a sound from the back door. I checked and found out that out of a sudden everything works again as it should. There was one thing I did to the electrics during the the day: I have an Eberspächer engine heater which also has a remote control. Afterresconnecting the battery the last time the control unit in the car showed nonsense signs on the display. I pressed the two buttons and worked until the display showed what it should. But I can hardly imagine that this procedure could have some connection with the centryl locking remote operation. The car was parked over night and everythin still works now in the morning.

Nice to have spontaneous healing with cars, too, not only spontaneous faults.

I was about 170 km near to Lourdes in my September holiday .... but with a rental car.

Franz47 EMail im Absender wird nie gelesen. Kontakt hier über die Newsgroup

On 06.10.2012 09:24, Franz47 wrote: > A spontaneous healing has taken place!!! It was only a short remission :-(

After driving today about 10 km the same behaviour as before. Only lights flashing, sometimes opening with remote control. Tailgate lock does not lock if 4 passenger doors lock with remote control. Tailgate lock mechanical operation locks the passenger doors.

Another idea before engaging more: Broken cable(s) between body and tailgate. The cables run throug the left hinge and are certainly quite stressed after 16 years of operation. I vagely remember that broken cables there can cause confusion in the central locking system.

I do not believe in the weak remote control battery theory. I operated the key several times in sequence yesterday evening and it worked fine.

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