There are 3 versions of the receiver, all operating in the 433.9 MHz licence free band which is for 'Momentarily Operated Low Power Devices'. The first generation are terrible and will respond to any transmission on that, and other nearby, frequency which means key fobs for other cars and other wireless devices such as doorbells, burglar alarm, weather stations, oil tank level senders, kids toys, etc. The selectivity was improved on the second generation but can still be affected and they both share the same problem. As soon as they receive a signal, they wake up the BeCM waiting for the correct code to unlock the car and turn off the immobiliser. If they get a signal but not the correct code, the BeCM goes to sleep after 2 minutes until the next time it is woken up which means in a densely populated area with lots of wireless devices, the BeCM can be constantly woken resulting in a flat battery in a very short time.
The third generation is completely different in as much as the receiver looks for a legitimate code before it wakes up the BeCM, so it will still wake it up if it sees a transmission from another P38 fob (as that will have the same preamble before the actual code) but won't wake up the BeCM if it receives a signal from anything else. So, if you find your battery goes flat overnight (or in 3 or 4 days if the car isn't used regularly), there is likely to be a source somewhere nearby that keeps waking the BeCM. The answer is to fit either a gen 3 receiver at around £400 or a Marty Cox filter. Marty developed the filter that plugs into the receiver that blocks the command to the BeCM unless it sees a legitimate P38 unlock code and is far cheaper than a gen 3 receiver (see http://www.p38webshop.co.uk/).
To check if yours is being affected, when the BeCM is awake the LED next to the gearchange lever will glow dimly and go out completely when it sleeps. So if you are suffering battery drain you can sit in the car at night looking at that.
Finding sources of interference was work before I retired and it isn't just the P38 that is affected, BMW cars of similar age were just as bad and so where a number of other makes.
Peterborough, Cambs
- '93 Range Rover Classic 4.2 LSE, sold
- '97 Range Rover 4.0SE, in Oxford Blue with a sort of grey/blue leather interior sold as two is plenty.....
- '96 4.6HSE Ascot - now sold
- '98 4.0SE in Rioja Red
'98 Ex-Greater Manchester Police motorway patrol car, Range Rover P38 4.0, in Chawton white - the everyday car
All running perfectly on LPG
- Proud to be a member of the YCHJCYA2PDTHFH club.