Key fob wont sync P38 1998

Hi,
I have problem with syncing my RR P38 1998 2.5TDS`s key fob.
Its all started when I changed keys batterys - I got ENGINE DISABLED message. Now every time I have to enter EKA code, but I`m worried that some day micro switches stops working or something like that and I wont be able to start car.

I have tried:
method in old (up to 1997) handbook
locking doors and pressing fobs buttons
locking doors and holding fobs buttons for 3 and more seconds
leaving key in pos II and pressing buttons
leaving key in pos I and pressing buttons
leaving key in pos I for 4-5h
leaving key in pos II for 4-5h

Maybe my ultra sonic sensor is dead, (sometimes I got ALARM FAULT message and alarm NEVER goes off) and it stops friendly resync ?

Any suggestions what I can try? :confused2:

PS> I`m from Latvia so I can`t go to any of you!

First of all have you got batteries in the correct way round. Does the LED light when you press the fob?

Yes, fob works and transmits signal. (locksmith tested it)

If it gives any hint :few mins ago measured volts to transmitter/reciever (rear right side near antenna) and ground:
When button is not pressed : 10.45V
When button is pressed: 10.25V

evo70 said:

Yes, fob works and transmits signal. (locksmith tested it)

If it gives any hint :few mins ago measured volts to transmitter/reciever (rear right side near antenna) and ground:
When button is not pressed : 9.95V
When button is pressed: 9.75V

Click to expand...

Then you need some diag on car to see what is stopping the syncing. All you should need to do with your year of car is either put fob in door lock press lock button and turn to lock then open or put key in ignition and press lock button and turn to position two. Don't know what the voltage should be at the RF receiver but 9.95 maybe a little low.

Ok have had a look. Pin 3 on RF receiver should have 12 volts fed from fuse 15 on BECM (20 amps). Pin 1 is signal so should have nothing until fob is pressed at a guess and a signal voltage when it is. Pin 2 is ground.

Ok I will try with key.
I editet my previus measurements, they were faulty. I will test one more time and post reults.

Edit: I measured again:
Pin 3: 12V,
Pin 1: when button in not presed:10.26V when button is pressed 10.04V (ground from car frame)

Your given method didnt work

Buy a kicker from black box solutions, when my fob battery died and after checking the forums I found i needed to Sync the the car to cancel out the engine immobiliser code. I had wore down the battery trying to get it started before I knew better. New battery in and it fixed the problem. Plugs into the port under the glove box. Keep it in the car at all times

evo70 said:

Ok I will try with key.
I editet my previus measurements, they were faulty. I will test one more time and post reults.

Edit: I measured again:
Pin 3: 12V,
Pin 1: when button in not presed:10.26V when button is pressed 10.04V (ground from car frame)

Your given method didnt work

Click to expand...

You need diag then something is not playing.

Stavros1967 said:

Buy a kicker from black box solutions, when my fob battery died and after checking the forums I found i needed to Sync the the car to cancel out the engine immobiliser code. I had wore down the battery trying to get it started before I knew better. New battery in and it fixed the problem. Plugs into the port under the glove box. Keep it in the car at all times

Click to expand...

Engine immobilised on message centre and ECM/BECM security sync are not the same thing. If the security code has become scrambled in the BECM there is no message telling you that. The engine just won't start, then you need the syncmate. Engine immobilaised message needs the fob code to be synced to the stored code in the BECM. Until that is done you would need to input the EKA code every time you start the car. EKA code and fob code are not the same thing.

evo70 said:

Ok I will try with key.
I editet my previus measurements, they were faulty. I will test one more time and post reults.

Edit: I measured again:
Pin 3: 12V,
Pin 1: when button in not presed:10.26V when button is pressed 10.04V (ground from car frame)

Your given method didnt work

Click to expand...

You will not get a sensible reading from pin 1 when the FOB is operated using a meter as you are trying to measure a sequence of pulses, you might just get a better idea with the meter set to AC but I doubt it. Needs a scope to see what is being sent to the BECM.
Diagnostics needed to see if a valid FOB code is being received, you could buy a Nanocom.
Try a PM to Mozz smith, he's good at re-syncing FOB's.