peter51
12th February 2019, 02:11 PM
I sent this to rangerovers.net to hopefully be added to their brilliant writeup on the P38 key FOBS/Remotes.
This should help others having trouble with troubleshooting the security system.
When you look carefully at the circuit inside the P38 key FOB you can see that the illumination of the LED has nothing to do with whether a signal via 433MHZ(Australia) is being transmitted. The LED is in series with the battery and lock/unlock micro switches only - so it just indicates whether battery voltage is OK or the switch is OK - certainly not that it is transmitting a burst of 433MHZ.
To test the handset it must be activated next to a RF detector set(available in some autoshops) in order to the observe an RF burst.
Without this information the diagnosis of a P38 locking issue can easily go astray. I.E. try to operate the locks - you notice the LED is operating - so you assume a valid RF transmission - so you assume it is not the key FOB and you start replacing other parts on the car. Therfore, using the LED to assume the FOB is serviceable leads you in the wrong direction.
My handset was illuminating the red LED on each press of the lock/unlock and yet there was no RF output at all - tested at an electronics workshop. I had an electronics professional solder in a new 433 MHZ SAW resonator(Australia). Before leaving his workshop we could observe that it was now transmitting a burst of RF each time we pressed lock or unlock - eventhough it was not synchronised to the vehicle. I returned to the P38 and carried out a synchronisation and now I have a fully functional FOB.
This should help others having trouble with troubleshooting the security system.
When you look carefully at the circuit inside the P38 key FOB you can see that the illumination of the LED has nothing to do with whether a signal via 433MHZ(Australia) is being transmitted. The LED is in series with the battery and lock/unlock micro switches only - so it just indicates whether battery voltage is OK or the switch is OK - certainly not that it is transmitting a burst of 433MHZ.
To test the handset it must be activated next to a RF detector set(available in some autoshops) in order to the observe an RF burst.
Without this information the diagnosis of a P38 locking issue can easily go astray. I.E. try to operate the locks - you notice the LED is operating - so you assume a valid RF transmission - so you assume it is not the key FOB and you start replacing other parts on the car. Therfore, using the LED to assume the FOB is serviceable leads you in the wrong direction.
My handset was illuminating the red LED on each press of the lock/unlock and yet there was no RF output at all - tested at an electronics workshop. I had an electronics professional solder in a new 433 MHZ SAW resonator(Australia). Before leaving his workshop we could observe that it was now transmitting a burst of RF each time we pressed lock or unlock - eventhough it was not synchronised to the vehicle. I returned to the P38 and carried out a synchronisation and now I have a fully functional FOB.