|P38 Range Rover Remote Key Fob Test|
If all the door locks fail to operate from the fob but work from pressing any of the door buttons then we have to test the remote signal into the becm. Partial failure ie. 1 or more doors not working are covered in their menu sections above.
Before following this test, first ensure the fob batteries are in good condition. They should be 3.0 volts. Brand new batteries although rated at 3.0 volts, will read approx 3.2-3.3 volts.
I have had many fobs work correctly yet they fail to light up the LED in the fob.
With all the becm plugs connected, put the positive probe of your voltmeter into the back of pin 6 and your earth to a good earth connection. (Use the Becm earth connection /black cable far left of becm fuse box) You should see a signal carrying voltage of approx 9-10 volts. It fluctuates slightly but only by a few millivolts. Press your remote fob and the voltage will fluctuate by a much more noticeable amount. Do this test a couple of times to be confident that the signal is there.
1: the remote fob is dead. (Using a fob tester is the only conclusive test)
2: The receiver or its power supply has failed.
3: There is a fault on the signal wire.
(Note: fault 3) The signal wire may have a short and you are seeing voltage from another circuit. The signal voltage is more noticeable as it constantly fluctuates.
Note: it is very rare for the receiver to fail but shouldn't be ruled out. Check the power supply which is fuse 15 of the Becm to pin 3 of the receiver, purple wire.
The earth connection of the receiver is the black wire on the 3 pin plug and goes straight to ground.
If the voltage reading is way out then check continuity and for a short to ground of the orange and red wire between pin 2 of the receiver to pin6 C326. (shown above)
If the signal is there but you still have no central locking you can break this down into 2 further faults:
1: The fob itself could have rolled its code. Repeated use of the fob without the vehicle responding can cause the remote to roll its code but the becm will not roll with it. This means the Fob no longer matches the becm.
2: You have had a flat battery or the battery has been disconnected and you have not carried out a key re sync or you have tried a key re sync and it is failing either because the code is incorrect, it has not been entered correctly, the becm is alarmed and will not accept it, or because the key lock switch is faulty.
With total locking failure it is advisable to remove the becm and have it tested.
If Some of the doors lock or unlock then read on.